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DETECTION AND CHARACTERIZATION OF ESCHERICHIA COLI O157:H7 AND SALMONELLA IN FOOD

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... After incubation, the TT broth was used to extract DNA of Salmonella as mentioned above. Method used for detection of Staphylococcus aureus in naturally contaminated food: Based on (22) Staph.aureus isolated from food samples including meats of (sheep ,fresh chicken, frozen chicken and beef) and vegetables including( lettuce, pepper, leek, tomato, celery ,cucumber) Twenty-five g of each sample were weighed and transferred into sterile Stomacher bags, containing 225 ml of Brain heart infusion broth in 37ºC water bath with shaking at 100 rpm/min for 6 h, and 1 ml preenriched rinse were transferred into to selective agar (Manitol salt agar) after incubation for 24 hours, this selective media was used to extract DNA of Staph.aureus as mentioned previously. ...
... The results in figure 4 showed 108 bp amplified products in four out of ten food samples which were positive for Staph. aureus including :tomato, lettuce, fresh chicken meat, frozen chicken meat , this is in agreement with (38,22) who detect Staph. aureus by PCR in less than 50% of naturally contaminated foods, this mean that the developed PCR-based, method was very effective in Staph.aureus ...
Article
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A rapid method for detection of food-borne pathogens, gene specific PCR, was used to detect two kinds of bacteria ( Salmonella spp. and Staphylococcus aureus) from food. Cultures of artificially inoculated foods were spiked ,with reference bacteria at known concentrations and DNA was isolated from each food sample before and after enrichment, using phenol -chloroform based method, Positive results were obtained using gene specific PCR (targeting the invA gene in Salmonella spp. and Sa 442 gene in Staphylococcus aureus ) just after enrichment step, that produced specific amplicons of the expected sizes which was 284bp in Salmonella spp. and 108 bp in Staphylococcus aureus. The detection limit of the assay was 103 CFU/ ml for the two kinds of bacteria. No results were obtained using the same primers with five other types of bacterial strains which improve it s specifity. The same technique was used for detection of the two kinds of bacteria in some naturally contaminated foods. To achieve this, 13 food samples were collected from Sulaymani market during April-October, 2012 including meats (meat of beef, sheep, goats, fresh chicken, and frozen chicken) and vegetables (celery, tomato, cucumber, pepper, lettuce, broccoli, carrot, and leek) DNA isolated from the samples after two enrichment steps ,the results of PCR, indicate the detection of Salmonella spp., in three out of 13 food samples tested, whereas the detection of Staphylococcus aureus achieved in four out of 10 food samples tested. This study indicate that PCR is a good way for the rapid detection of Salmonella spp and Staphylococcus aureus in food. Key words : Identification , gene specific PCR, food-borne pathogens.
... From (Tables 7 & 8) showed the incidence and serotyping of Salmonella isolated from cooked meat and chicken meals is 6.67% from meat identified serologically as S. Heidelberg O 4,5,12 : H r:1,2 6.67% from beef kofta identified serologically as S. Montevideo O 6,7,14 : H g,m,s:1,7,2 6.67% from chicken identified serologically as S. Kentucky O 8,20 : H i:Z6 20% from chicken kofta identified serologically as S. Anatum O 1, 9,12 : H g,m:1,7 (6.67%), S. Infant is O 6,7,14 : H r:1,5 (6.67%) and S. Typhimurium O 1,4,5,12 : H i:1,2 (6.67%). Salmonella microorganisms were previously isolated from cooked meat meals by [22,23] also salmonella failed to be isolated from cooked meat meals by [24] the symptoms the symptoms of salmonellosis include diarrhea, nausea, vomiting, fever and abdominal cramps [25]. ...
Article
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Sixty random samples (15 of each) were collected from different restaurants to evaluate their bacteriological quality. The mean values of APC, Enterobacteriacae, coliform counts (cfu/g) were 6.03×103 ± 1.45×103 , 3.16×103 ± 0.72×103 , 7.43×102 ± 1.05×102 for meat, 8.58×103 ± 1.65×103 , 6.53×103 ± 1.24×103, 9.18×102 ± 2.07×103 for chicken, 9.91×103 ± 2.18×103 , 5.25×103 ± 0.86×103 , 1.06×103 ± 0.19×102 for beef kofta and 2.03×104 ± 0.43×104 , 9.14×103 ± 2.06×103 , 3.32×103 ± 0.45×103 for chicken kofta, respectively. The results showed that 12 isolates of E.coli were identified from examined ready to eat chicken and meat meals with different per- centages (O26 : H11, O111 : H4 , O124, O78, O91 : H21, O121 : H7 , O127 : H6 , O146 : H21) E.coli strains were serologically identified from such examined meals, there are 6 isolates of Salmonella were identified from examined samples. Also, there are 21 isolates of Staph aureus were isolated from examined samples represented as 20% from meat, 40% from beef kofta, 33.33% from chicken and 46.67% from chicken kofta.
... Also, salmonella failed to be isolated from ready to eat meat meals by Kirralla (2007). The symptoms of salmonellosis include diarrhea, nausea, vomiting, fever and abdominal cramps (Cui, 2004). The results in Table ( 9) reported that Staph. ...
Article
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Sixty random samples of ready to eat chicken and meat meals including meat, chicken, beef kofta and chicken kofta (15 of each) were collected from different restaurants from Tanta city to evaluate their bacteriological quality The mean values of Areobic plate count(APC) , Enterobacteriacae, coliform counts(CFU/g) were 6.03×103 ± 1.45, 3.16×103 ± 0.72,7.43×102 ± 1.05 for meat,8.58×103 ± 1.65,6.53×103 ± 1.24,9.18×102 ± 2.07 for chicken , 9.91×103 ± 2.18, 5.25×103 ± 0.86, 1.06×103 ± 0.19 for beef kofta and 2.03×104 ± 0.43, 9.14×103 ± 2.06,3.32×103 ± 0.45 for chicken kofta, respectively. The results showed that 12 isolates of E.coli were identified from the examined ready to eat chicken and meat meals with different percentages as follow O26: H11 EHEC (6.67%)& O111: H4 EHEC (6.67%) for meat, O26: H11 EHEC (13.33%)& O124 EIEC (6.67%) for beef kofta, O78 EPEC(6.67%)&O127:H6 ETEC(6.67%)&O146:H21EPEC(6.67%) for chicken and O26:H11EHEC(13.33%)&O91:H21EHEC(6.67%)&O121:H7 EHEC(6.67%) for chicken kofta. Also there are 6 isolates of salmonella from the examined meals were identified. Also, there are 21 S.aureus from examined samples represented as 20% from meat, 40% from beef kofta, 33.33% from chicken and 46.67% from chicken kofta. Thus the current results in this study allowing concluding that all examined samples were contaminated with different bacteria as E.coli, Salmonella and S.aureus. And the highest APC was in chicken kofta followed with beef kofta, chicken and meat.
... Salmonella organisms may be commonly carried by human and animal, when those bacteria are multiplied in the intestine they become pathogenic and causing intestinal disorder and slight or sever infection and may even cause death [24]. The symptoms of salmonellosis include diarrhea, nausea, vomiting, fever and abdominal cramps [5]. Low incidence of Salmonella isolation may be attributed to the fact that most pathogenic bacteria destroyed between 72 ْC to 83 ْC so the cooking method should be effectively applied to produce temperature sufficient to kill all these pathogens [26]. ...
Conference Paper
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One hundred random samples of cooked head meat, liver, kofta and mixed offal (25 of each) were collected from street vendors level in Kalyobia, Giza and Cairo governorates. All collected samples were examined to determine their microbiological profiles. The obtained results indicated that the mean values of APC, Enterobacteriaceae and coliform counts in the examined samples of cooked meat products were 1.4 x 107 0.5 x 107 , 1.7 x 104  0.43 x 104 , 3.4 x 105  0.17 x 105 CFU /g, for liver, 1.2 x 107  0.4 x 107 , 2.4 x 104  0.52 x 104 , 9.6 x 105  0.37 x 105 CFU /g, for mixed offal, 1.5 x 107  0.43 x 107 , 1.5 x 107  0.48 x 107 , 2.6 x 105  0.5 x 105 CFU /g for kofta, 5.4 x 106 0.33 x 106 , 2 x 103  0.58 x 103 , 1.4 x 103  0.44 x 103 CFU /g, for head meat, respectively. The differences associated with the examined samples of cooked meat products were significant (P < 0.05) because of product type. Concerning Salmonella organisms, S. entritidis was isolated from (8%, 12%, 4%) of liver, mixed offal and kofta respectively. In addition, S.typhimurium was isolated from 8% and 4% of the examined samples of liver and kofta, retailed at low level of sanitation, respectively. While, all examined samples of cooked head meat products were free from Salmonellae. Finally, the significance of isolated bacteria in ready- to- eat meat products and possible sources of contamination as well as some recommendations to improve the quality of these products were discussed.
... Salmonella organisms may be commonly carried by human and animal, when those bacteria are multiplied in the intestine they become pathogenic and causing intestinal disorder and slight or sever infection and may even cause death [24]. The symptoms of salmonellosis include diarrhea, nausea, vomiting, fever and abdominal cramps [5]. Low incidence of Salmonella isolation may be attributed to the fact that most pathogenic bacteria destroyed between 72 ْC to 83 ْC so the cooking method should be effectively applied to produce temperature sufficient to kill all these pathogens [26]. ...
... Salmonella organisms may be commonly carried by human and animal, when those bacteria are multiplied in the intestine they become pathogenic and causing intestinal disorder and slight or sever infection and may even cause death (Marriott ,1997). The symptoms of salmonellosis include diarrhea, nausea, vomiting, fever and abdominal cramps (Cui ,2004). ...
... The large effect of antibiotic growth promoter bans relative to those of other interventions may therefore be due to the different comparator groups across the different interventions. Lending support to this hypothesis is that growth promoter ban studies tended to be published earlier (median year of publication , IQR 2000-2004) compared with studies examining all other types of interventions (median 2010(median , IQR 2006(median -2015. Further support is provided through stratified meta-analysis of baseline proportions of isolates demonstrating antibiotic resistance. ...
Article
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Background We have previously reported, in a systematic review of 181 studies, that restriction of antibiotic use in food-producing animals is associated with a reduction in antibiotic-resistant bacterial isolates. While informative, that report did not concretely specify whether different types of restriction are associated with differential effectiveness in reducing resistance. We undertook a sub-analysis of the systematic review to address this question. Methods We created a classification scheme of different approaches to antibiotic restriction: (1) complete restriction; (2) single antibiotic-class restriction; (3) single antibiotic restriction; (4) all non-therapeutic use restriction; (5) growth promoter and prophylaxis restriction; (6) growth promoter restriction and (7) other/undetermined. All studies in the original systematic review that were amenable to meta-analysis were included into this substudy and coded by intervention type. Meta-analyses were conducted using random effects models, stratified by intervention type. Results A total of 127 studies were included. The most frequently studied intervention type was complete restriction (n=51), followed by restriction of non-therapeutic (n=33) and growth promoter (n=19) indications. None examined growth promoter and prophylaxis restrictions together. Three and seven studies examined single antibiotic-class and single antibiotic restrictions, respectively; these two intervention types were not significantly associated with reductions in antibiotic resistance. Though complete restrictions were associated with a 15% reduction in antibiotic resistance, less prohibitive approaches also demonstrated reduction in antibiotic resistance of 9%–30%. Conclusion Broad interventions that restrict global antibiotic use appear to be more effective in reducing antibiotic resistance compared with restrictions that narrowly target one specific antibiotic or antibiotic class. Importantly, interventions that allow for therapeutic antibiotic use appear similarly effective compared with those that restrict all uses of antibiotics, suggesting that complete bans are not necessary. These findings directly inform the creation of specific policies to restrict antibiotic use in food-producing animals.
... Salmonella organisms may be commonly carried by human and animal, when those bacteria are multiplied in the intestine they become pathogenic and causing intestinal disorder and slight or sever infection and may even cause death [24]. The symptoms of salmonellosis include diarrhea, nausea, vomiting, fever and abdominal cramps [5]. Low incidence of Salmonella isolation may be attributed to the fact that most pathogenic bacteria destroyed between 72 ْC to 83 ْC so the cooking method should be effectively applied to produce temperature sufficient to kill all these pathogens [26]. ...
Article
Full-text available
One hundred random samples of cooked head meat, liver, kofta and mixed offal (25 of each) were collected from street vendors level in Kalyobia, Giza and Cairo governorates. All collected samples were examined to determine their microbiological profiles. The obtained results indicated that the mean values of APC, Enterobacteriaceae and coliform counts in the examined samples of cooked meat products were 1.4 x 107 0.5 x 107, 1.7 x 104  0.43 x 104 , 3.4 x 105  0.17 x 105 CFU /g, for liver, 1.2 x 107  0.4 x 107, 2.4 x 104  0.52 x 104, 9.6 x 105  0.37 x 105 CFU /g, for mixed offal, 1.5 x 107  0.43 x 107, 1.5 x 107  0.48 x 107, 2.6 x 105  0.5 x 105 CFU /g for kofta, 5.4 x 106 0.33 x 106, 2 x 103  0.58 x 103 , 1.4 x 103  0.44 x 103 CFU /g, for head meat, respectively. The differences associated with the examined samples of cooked meat products were significant (P < 0.05) because of product type. Concerning Salmonella organisms, S. entritidis was isolated from (8%, 12%, 4%) of liver, mixed offal and kofta respectively. In addition, S.typhimurium was isolated from 8% and 4% of the examined samples of liver and kofta, retailed at low level of sanitation, respectively. While, all examined samples of cooked head meat products were free from Salmonellae. Finally, the significance of isolated bacteria in ready- to- eat meat products and possible sources of contamination as well as some recommendations to improve the quality of these products were discussed.
... Bu serotiplerin hepsinin patojenite gösterdiği, 150 tanesinin insanlarda enfeksiyona sebep olduğu bildirilmiştir. İnsanlarda enfeksiyona sebep olan en yaygın 4 serotip S.Typhimurium, S. Enteritis, S. Newport ve S. Heidelberg'dir (Cui, 2004). Salmonella bakterileri yaklaşık 2.0-5.0 mikrometre boyunda, 0.7-1.5 mikrometre eninde sporsuz, kapsülsüz çomakçık şeklinde tüm Salmonella türleri, S. Pullorum ve S. Gallinarum dışında,peritrik flagellaları ile hareket yeteneğine sahiptirler. ...
... Also, salmonella failed to be isolated from cooked meat meals by [21]. The symptoms the symptoms of salmonellosis include diarrhoea, nausea, vomiting, fever and abdominal cramps [22]. The results in Tables 9 and 10 reported that staph .aureus ...
Article
Full-text available
Sixty random samples (15 of each) were collected from different restaurants to evaluate their bacteriological quality The mean values of APC, Enterobacteriaceae, coliform counts(cfu/g) were 6.03×103 ± 1.45×103 , 3.16×103 ± 0.72×103 , 7.43×102 ± 1.05×102 for meat, 8.58×103 ± 1.65×103 ,6.53×103 ± 1.24×103 , 9.18×102 ± 2.07×103 for chicken, 9.91×103 ± 2.18×103 , 5.25×103 ± 0.86×103 , 1.06×103 ± 0.19×102 for beef kofta and 2.03×104 ± 0.43×104 , 9.14×103 ± 2.06×103 , 3.32×103 ± 0.45×103 for chicken kofta, respectively. The results showed that 12 isolates of E.coli were identified from examined ready to eat chicken and meat meals with different percentages(O26 : H11, O111 : H4 , O124, O78,O91 : H21, O121 : H7 , O127 : H6 , O146 : H21) E.coli strains were serologically identified from such examined meals, there are 6 isolates of salmonella were identified from examined samples. Also, there are 21 isolates of staph. aureus were isolated from examined samples represented as 20% from meat,40% from beef kofta,33.33% from chicken and 46.67% from chicken kofta.
... e antimicrobials including sulfisoxazole, spectinomycin, amoxicillin/clavulanic acid, ampicillin, tetracycline, chloramphenicol, florfenicol and streptomycin. The high levels of resistant Salmonella isolates to one or more antimicrobials in present study and previous studies may be due to the worldwide overuse of antimicrobials in different fields. Cui (2004) has isolated 27 (44%) Salmonella from 61 chicken samples and found that the 100% Salmonella Typhimurium were resistant to amoxicillin/clavulanic acid, ampicillin, cephalothin, ceptiofur and cefoxitin. On the contrary, all Salmonella isolates were susceptible to ampicillin, amoxicillin, ciprofloxacin , chloramphenicol, gentamicin, kanamy ...
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In this study, 32 Salmonella strains isolated from 400 chicken carcasses were serotyped, and antibiotic resistance profiles were detected against 12 selected antimicrobial agents using disc diffusion method. Thirty-two isolates were identified as follows; 22 (68.7%) Salmonella Enteritidis, five (15.6%) Salmonella Virchow, three (9.3%) Salmonella Typhimurium and two (6.2%) Salmonella Hadar. In all Salmonella isolates, antibiotic resistance were detected. Out of 32 Salmonella strains, 22 (68.75%) displayed multi-drug resistance. Thirty-two (100.0%) of the isolates were found to be resistant to penicillin G, 20 (62.5%) to nalidixic acid, four (12.5%) to cephalothin, two (6.2%) to streptomycin and two (6.2%) to tetracycline. Fifteen (68.1%) Salmonella Enteritidis, one (33.3%) Salmonella Typhimurium, two (100.0%) Salmonella Hadar and two (40.0%) Salmonella Virchow were shown to be resistant to nalidixic acid. Cephalothin resistance was detected in 9.0%, 33.3%, and 20.0% for Salmonella Enteritidis, Salmonella Typhimurium and Salmonella Virchow, respectively. The results indicate that Salmonella recovered from chicken carcasses were resistant to multiple antimicrobials and that resistance among these isolates varies by serotype. Also, this emerged as a significant public health problem.
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Sixty random samples (15 of each) were collected from different restaurants to evaluate their bacteriological quality The mean values of APC, Enterobacteriaceae, coliform counts(cfu/g) were 6.03×103 ±1.45×103 , 3.16×103 ±0.72×103 , 7.43×102 ±1.05×102 for meat,8.58×103 ±1.65×103 ,6.53×103 ±1.24×103 , 9.18×102 ±2.07×103 for chicken, 9.91×103 ±2.18×103 , 5.25×103 ±0.86×103 ,1.06×103 ±0.19× 102 for beef kofta and 2.03×104 ±0.43×104,9.14×103 ±2.06×103 ,3.32×103 ±0.45×103 for chicken kofta, respectively. The results showed that 12 isolates of Escherichia coli were identified from examined ready to eat chicken and meat meals with different percentages(O26:H11, O111:H4 , O124, O78,O91:H21, O121:H7 , O127:H6, O146:H21) Escherichia coli strains were serologically identified from such examined meals, there are 6 isolates of salmonella were identified from examined samples. Also, there are 21 isolates of staph aureus were isolated from examined samples represented as 20% from meat,40% from beef kofta,33.33% from chicken and 46.67% from chicken kofta [1-4].
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Full-text available
Sixty random samples (15 of each) were collected from different restaurants to evaluate their bacteriological quality The mean values of APC, Enterobacteriaceae, coliform counts(cfu/g) were 6.03×103 ±1.45×103 , 3.16×103 ±0.72×103 , 7.43×102 ±1.05×102 for meat,8.58×103 ±1.65×103 ,6.53×103 ±1.24×103 , 9.18×102 ±2.07×103 for chicken, 9.91×103 ±2.18×103 , 5.25×103 ±0.86×103 ,1.06×103 ±0.19× 102 for beef kofta and 2.03×104 ±0.43×104,9.14×103 ±2.06×103 ,3.32×103 ±0.45×103 for chicken kofta, respectively. The results showed that 12 isolates of Escherichia coli were identified from examined ready to eat chicken and meat meals with different percentages(O26:H11, O111:H4 , O124, O78,O91:H21, O121:H7 , O127:H6, O146:H21) Escherichia coli strains were serologically identified from such examined meals, there are 6 isolates of salmonella were identified from examined samples. Also, there are 21 isolates of staph aureus were isolated from examined samples represented as 20% from meat,40% from beef kofta,33.33% from chicken and 46.67% from chicken kofta [1-4].
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Antimicrobial resistance is considered one of the greatest threats to global and public health today. The World Health Organization, the Food and Agriculture Organization, and the World Organisation for Animal Health, known as the Tripartite Collaboration, have called for urgent action. We have previously published a systematic review of 181 studies, demonstrating that interventions that restrict antibiotic use in food-producing animals are associated with a reduction in antibiotic resistant bacterial isolates in both animals and humans. What remains unknown, however, are whether (and what) unintended consequences may arise from such interventions. We therefore undertook a sub-analysis of the original review to address this research question. A total of 47 studies described potential consequences of antibiotic restrictions. There were no consistent trends to suggest clear harm. There may be increased bacterial contamination of food products, the clinical significance of which remains unclear. There is a need for rigorous evaluation of the unintended consequences of antibiotic restrictions in human health, food availability, and economics, given their possible widespread implications.
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Sixty random samples (15 of each) were collected from different restaurants to evaluate their bacteriological quality The mean values of APC, Enterobacteriaceae, coliform counts(cfu/g) were 6.03×103 ±1.45×103 , 3.16×103 ±0.72×103 , 7.43×102 ±1.05×102 for meat,8.58×103 ±1.65×103 ,6.53×103 ±1.24×103 , 9.18×102 ±2.07×103 for chicken, 9.91×103 ±2.18×103 , 5.25×103 ±0.86×103 ,1.06×103 ±0.19× 102 for beef kofta and 2.03×104 ±0.43×104,9.14×103 ±2.06×103 ,3.32×103 ±0.45×103 for chicken kofta, respectively. The results showed that 12 isolates of Escherichia coli were identified from examined ready to eat chicken and meat meals with different percentages(O26:H11, O111:H4 , O124, O78,O91:H21, O121:H7 , O127:H6, O146:H21) Escherichia coli strains were serologically identified from such examined meals, there are 6 isolates of salmonella were identified from examined samples. Also, there are 21 isolates of staph aureus were isolated from examined samples represented as 20% from meat,40% from beef kofta,33.33% from chicken and 46.67% from chicken kofta [1-4].
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Sixty random samples (15 of each) were collected from different restaurants to evaluate their bacteriological quality The mean values of APC, Enterobacteriaceae, coliform counts(cfu/g) were 6.03×103 ±1.45×103 , 3.16×103 ±0.72×103 , 7.43×102 ±1.05×102 for meat,8.58×103 ±1.65×103 ,6.53×103 ±1.24×103 , 9.18×102 ±2.07×103 for chicken, 9.91×103 ±2.18×103 , 5.25×103 ±0.86×103 ,1.06×103 ±0.19× 102 for beef kofta and 2.03×104 ±0.43×104,9.14×103 ±2.06×103 ,3.32×103 ±0.45×103 for chicken kofta, respectively. The results showed that 12 isolates of Escherichia coli were identified from examined ready to eat chicken and meat meals with different percentages(O26:H11, O111:H4 , O124, O78,O91:H21, O121:H7 , O127:H6, O146:H21) Escherichia coli strains were serologically identified from such examined meals, there are 6 isolates of salmonella were identified from examined samples. Also, there are 21 isolates of staph aureus were isolated from examined samples represented as 20% from meat,40% from beef kofta,33.33% from chicken and 46.67% from chicken kofta [1-4].
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Sixty random samples (15 of each) were collected from different restaurants to evaluate their bacteriological quality The mean values of APC, Enterobacteriaceae, coliform counts(cfu/g) were 6.03×103 ±1.45×103 , 3.16×103 ±0.72×103 , 7.43×102 ±1.05×102 for meat,8.58×103 ±1.65×103 ,6.53×103 ±1.24×103 , 9.18×102 ±2.07×103 for chicken, 9.91×103 ±2.18×103 , 5.25×103 ±0.86×103 ,1.06×103 ±0.19× 102 for beef kofta and 2.03×104 ±0.43×104,9.14×103 ±2.06×103 ,3.32×103 ±0.45×103 for chicken kofta, respectively. The results showed that 12 isolates of Escherichia coli were identified from examined ready to eat chicken and meat meals with different percentages(O26:H11, O111:H4 , O124, O78,O91:H21, O121:H7 , O127:H6, O146:H21) Escherichia coli strains were serologically identified from such examined meals, there are 6 isolates of salmonella were identified from examined samples. Also, there are 21 isolates of staph aureus were isolated from examined samples represented as 20% from meat,40% from beef kofta,33.33% from chicken and 46.67% from chicken kofta [1-4]
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The influence of pH adjusted with lactic acid or HCl or sodium chloride concentration on survival or growth of Escherichia coli O157:H7 in Trypticase soy broth (TSB) was determined. Studies also determined the fate of E. coli O157:H7 during the production and storage of fermented, dry sausage. The organism grew in TSB containing less than or equal to 6.5% NaCl or at a pH of 4.5 to 9.0, adjusted with HCl. When TSB was acidified with lactic acid, the organism grew at pH 4.6 but not at pH 4.5. A commercial sausage batter inoculated with 4.8 x 10(4) E. coli O157:H7 per g was fermented to pH 4.8 and dried until the moisture/protein ratio was less than or equal to 1.9:1. The sausage chubs were then vacuum packaged and stored at 4 degrees C for 2 months. The organism survived but did not grow during fermentation, drying, or subsequent storage at 4 degrees C and decreased by about 2 log10 CFU/g by the end of storage. These studies reveal the importance of using beef containing low populations or no E. coli O157:H7 in sausage batter, because when initially present at 10(4) CFU/g, this organism can survive fermentation, drying, and storage of fermented sausage regardless of whether an added starter culture was used.
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RAPID and simple methods for the detection and isolation of Salmonella from foods and feeds have been the subject of much research and investigation. A detailed discussion of the conventional biochemical methods of detecting and isolating Salmonella in foods and feeds was made by Galton et al. (1968). The use of fluorescent antibody for rapid detection of Salmonella in animal food products was reviewed by Ayres (1967). However, all these procedures are time consuming (48–96 hr.) and laborious or require special equipment such as a microscope with fluorescence equipment. Schafer et al. (1968) reported on the use of reagent tablets for rapid biochemical confirmation of Salmonellae after isolation on selective agar. A glass apparatus for determining the presence of Salmonella in mixed cultures was described by Banwart (1968). Also, Banwart et al. (1968) developed a screening method for determining Salmonella-negative samples of pasteurized dried whole egg. With most conventional…
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Two experiments were conducted to compare effects of housing temperatures and bird density on the airborne microflora of poultry houses. Temperatures of 15.6 and 26.7 C were used with birds housed at densities of .42 or .84 m3 per bird. Air samples were taken using a New Brunswick STA 200 microbiological air sampler. Numbers of aerobic, anaerobic, coliform and lactic acid bacteria, and molds were determined by plate counts with numbers of Escherichia coli and Staphylococcus aureus determined by most probable numbers procedures. Microorganisms were identified by picking representative colonies from plates and inoculating into differential media for biochemical tests. Higher bird density (.42 m3/bird) resulted in greater numbers of airborne microorganisms in both experiments. Fifteen genera of bacteria were identified with two or more species identified for eight genera. Among the most commonly identified aerobic genera were Bacillus, Micrococcus, Proteus, Pseudomonas and Staphylococcus, while four species of Clostridia were the most frequently identified anaerobes. Nine genera of molds were identified with over one-half of all isolates being either Aspergillus or Penicillium. Microorganisms represented only a small fraction of the airborne particulate matter in the study.
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Several members of the family Enterobacteriaceae were examined for differences in extreme acid survival strategies. A surprising degree of variety was found between three related genera. The minimum growth pH of Salmonella typhimurium was shown to be significantly lower (pH 4.0) than that of either Escherichia coli (pH 4.4) or Shigella flexneri (pH 4.8), yet E. coli and S. flexneri both survive exposure to lower pH levels (2 to 2.5) than S. typhimurium (pH 3.0) in complex medium. S. typhimurium and E. coli but not S. flexneri expressed low-pH-inducible log-phase and stationary-phase acid tolerance response (ATR) systems that function in minimal or complex medium to protect cells to pH 3.0. All of the organisms also expressed a pH-independent general stress resistance system that contributed to acid survival during stationary phase. E. coli and S. flexneri possessed several acid survival systems (termed acid resistance [AR]) that were not demonstrable in S. typhimurium. These additional AR systems protected cells to pH 2.5 and below but required supplementation of minimal medium for either induction or function. One acid-inducible AR system required oxidative growth in complex medium for expression but successfully protected cells to pH 2.5 in unsupplemented minimal medium, while two other AR systems important for fermentatively grown cells required the addition of either glutamate or arginine during pH 2.5 acid challenge. The arginine AR system was only observed in E. coli and required stationary-phase induction in acidified complex medium. The product of the adi locus, arginine decarboxylase, was responsible for arginine-based acid survival.
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A study was undertaken to determine the fate of Escherichia coli O157:H7 in ground, roasted beef as influenced by the combined effects of pH, acidulants, temperature, and time. There was essentially no change in the viable population of E. coli O157:H7 when beef salads (pH 5.40 to 6.07) containing up to 40% mayonnaise were incubated at 5 degrees C for up to 72 h. At 21 and 30 degrees C, significant (P < or = 0.05) increases in populations of the organism occurred in salads containing 16 to 32% mayonnaise (pH 5.94 to 5.55) between 10 and 24 h of incubation. Death was more rapid as the pH of acidified beef slurries incubated at 5 degrees C was decreased from 5.98 to 4.70. E. coli O157:H7 grew in control slurries (pH 5.98) and in slurries containing citric and lactic acids (pHs 5.00 and 5.40) incubated at 21 degrees C for 24 h; decreases occurred in slurries acidified to pHs 4.70, 5.00, and 5.40 with acetic acid or pH 4.70 with citric or lactic acid. At 30 degrees C, populations decreased in slurries acidified to pHs 4.70 and 5.00 with acetic acid. Citric and lactic acids failed to prevent significant increases in populations in slurries at pH 4.70 to 5.40 between 10 and 24 h of incubation. The order of effectiveness of acidulants in inhibiting growth was acetic acid > lactic acid > or = citric acid. The same order was observed for inactivation of E. coli O157:H7 in acidified (pH 5.00) beef slurry heated at 54 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
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Shigella species require a uniquely small inoculum for causing dysentery. One explanation for the low infective dose is that Shigella species are better able to survive the acidic conditions encountered in the stomach than are other enteric pathogens. We have tested Shigella species, Escherichia coli, and Salmonella species for the ability to survive at pH 2.5 for at least 2 h. Most isolates of Shigella and E. coli survived this treatment, whereas none of the Salmonella isolates were able to do so. The ability of Shigella species to survive at low pHs does not require the presence of the large virulence plasmid or growth at 37 degrees C but is strikingly dependent on growth phase. We have also found that Shigella isolates exposed to acid lose the ability to invade epithelial cells.
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Stationary-phase cultures of Escherichia coli can survive several hours or exposure to extreme acid (pH 2 to 3), a level well below the pH range for growth (pH 4.5 to 9). To identify the genes needed for survival in extreme acid, a microliter screening procedure was devised. Colonies from a Tn10 transposon pool in E. coli MC4100 were inoculated into buffered Luria broth, pH 7.0, in microtiter wells, grown overnight, and then diluted in Luria broth, pH 2.5, at 37 degrees C for 2 h. From 3,000 isolates screened, 3 Tet(r) strains were identified as extremely acid sensitive (<0.1% survival at pH 2.5 for 2 h). Flanking sequences of the Tn10 inserts were amplified by inverse PCR. The sequences encoded a hydrophobic partial peptide of 88 residues. A random-primer-generated probe hybridized to Kohara clones 279 and 280 at 32 min (33.7 min on the revised genomic map EcoMap7) near gadB (encoding glutamate decarboxylase). The gene was designated xasA for extreme acid sensitive. xasA::Tn10 strains grown at pH 7 to 8 showed 100-fold-less survival in acid than the parent strain. Growth in mild acid (pH 5 to 6) restored acid resistance; anaerobiosis was not required, as it is for acid resistance in rpoS strains. xasA::Tn10 eliminated enhancement of acid resistance by glutamic acid. xasA was found to be a homolog of gadC recently sequenced in Shigella flexneri, in which it appears to encode a permease for the decarboxylated product of GadB. These results suggest that GadC (XasA) participates in a glutamate decarboxylase alkalinization cycle to protect E. coli from cytoplasmic acidification. The role of the glutamate cycle is particularly important for cultures grown at neutral pH before exposure to extreme acid.
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Enterohemorrhagic strains of Escherichia coli must pass through the acidic gastric barrier to cause gastrointestinal disease. Taking into account the apparent low infectious dose of enterohemorrhagic E. coli, 11 O157:H7 strains and 4 commensal strains of E. coli were tested for their abilities to survive extreme acid exposures (pH 3). Three previously characterized acid resistance systems were tested. These included an acid-induced oxidative system, an acid-induced arginine-dependent system, and a glutamate-dependent system. When challenged at pH 2.0, the arginine-dependent system provided more protection in the EHEC strains than in commensal strains. However, the glutamate-dependent system provided better protection than the arginine system and appeared equally effective in all strains. Because E. coli must also endure acid stress imposed by the presence of weak acids in intestinal contents at a pH less acidic than that of the stomach, the ability of specific acid resistance systems to protect against weak acids was examined. The arginine- and glutamate-dependent systems were both effective in protecting E. coli against the bactericidal effects of a variety of weak acids. The acids tested include benzoic acid (20 mM; pH 4.0) and a volatile fatty acid cocktail composed of acetic, propionic, and butyric acids at levels approximating those present in the intestine. The oxidative system was much less effective. Several genetic aspects of E. coli acid resistance were also characterized. The alternate sigma factor RpoS was shown to be required for oxidative acid resistance but was only partially involved with the arginine- and glutamate-dependent acid resistance systems. The arginine decarboxylase system (including adi and its regulators cysB and adiY) was responsible for arginine-dependent acid resistance. The results suggest that several acid resistance systems potentially contribute to the survival of pathogenic E. coli in the different acid stress environments of the stomach (pH 1 to 3) and the intestine (pH 4.5 to 7 with high concentrations of volatile fatty acids). Of particular importance to the food industry was the finding that once induced, the acid resistance systems will remain active for prolonged periods of cold storage at 4 degrees C.
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A detection system based on the PCR has been developed for Escherichia coli strains which harbor the Shiga-like toxin genes. This quantitative detection system involves the 5'-->3' nuclease activity of Thermus aquaticus DNA polymerase, which cleaves an internal oligonucleotide probe that has been labeled with both a fluorescent reporter dye (6-carboxy-fluorescein [FAM]) and a quencher dye (6-carboxytetramethyl-rhodamine [TAMRA]). Parameters which affected the performance of the assay included primer probe distance, probe concentration, and probe target sequence homology. The optimized assay format includes two PCR primers that generate a 497-bp amplicon specific for the sltI gene with the fluorogenic probe located 19 bp from the upstream PCR primer. When the distance between the upstream PCR primer and the probe was reduced from 190 to 19 bp, delta RQ values increased from approximately 1.5 to 3.0. The delta RQ for Shiga-like toxin I probe 102 reached a maximum of 4.15 at concentrations between 25 and 50 nM. The assay is sensitive and can detect approximately 10 +/- 5 CFU per PCR. As few as 0.5 CFU of Shiga-like toxin I-producing E. coli per g could be detected in ground beef with only 12 h of enrichment in modified E. coli broth.
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Municipal water samples were analyzed by membrane filter (MF) procedures for total coliforms, "background" counts, and 24-and 48-h, 35 °C plate counts. Presence–absence (P–A) tests were done on the samples for total coliforms and other indicator bacteria. The frequency of detection of indicator organisms by P–A tests was better than twice that recovered by MF analyses. When the 24-h plate count data were grouped into counting ranges of 0, 1–100, 101–1000, and > 1000, a marked inhibition effect was observed with total coliform MF recoveries on samples producing plate counts > 1000/mL. When the "background" and 48-h plate count results were placed in the corresponding counting ranges, inhibition of indicator organisms in the total coliform MF analyses was not observed. No inhibition effect was observed in the recovery of indicator organisms by P–A tests at any of the counting range levels. The presence of an apparent inhibition effect by high numbers of bacteria in a sample was shown to be influenced by the incubation period and type of count parameter, as well as the isolation technique for detection of indicator organisms.
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Current practices for preventing microbial diseases rely upon careful control of various kinds of pathogenic bacteria in food safety and environmental monitoring. The main disadvantages of conventional bacterial detection methods are the multistep procedure and long time requirements. This article gives an overview of alternative electrochemical biosensors for detection of pathogenic bacteria in the food industry. Focus has been on new microbial metabolism-based, antibody-based and DNA-based biosensors. The underlying principles and applications of these biosensors are discussed. Recent developments in flow-injection biosensor systems with an electrochemical detection are also presented.
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The objective of this study was to investigate the potential value of individual and combined applications of some GRAS (generally regarded as safe) additives with freezing and pulsed electric field (PEF) application, in reducing the risks associated with the presence of E. coli O157:H7 in beef burgers. Beef burgers, trimmings and filter paper were inoculated with E. coli O157:H7 and subjected to a range of chemical and physical treatments. Sequential application of 2% (v/v) lactic acid and freezing (at - 20 degrees C for 2 h) resulted in a decrease of approximately 6 log10 cfu cm(-1) in E. coli O157:H7, but only on filter paper. All other treatments were ineffective. Currently available methods for controlling E.coli O157:H7 in beef burgers during production are ineffective. Further research is needed to develop controls for E. coli O157:H7 during beef burger production.
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Four selective enrichment broths were compared for the detection of Salmonella spp. in naturally contaminated poultry products and the recovery of atypical Salmonella strains in suspensions of pure cultures. In analysis of 100 poultry samples, the sensitivities observed were 94.0% for Müller-Kauffmann Tetrathionate-Brilliant Green (MKTBG), 97.6% for Rappaport Vassiliadis (RV), 42.2% for Selenite Cystine (SC) and 97.6% for the new broth KIMAN (Whitley Impedance Broth supplemented with 20 mg/l of novobiocin sodium salt, 10 mg/l of malachite green oxalate and 40 g/l of potassium iodide). The two most efficient broths--RV and KIMAN for recovery of atypical Salmonella strains (gallinarum biotypes gallinarum and pullorum, typhi, paratyphi A) were less toxic than MKTBG but more toxic than s.c. broth. According to these results, the use of RV and KIMAN could be a good combination to assure maximal recovery of Salmonella strains.
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The reductase catalyzing the reduction of tetrathionate and thiosulphate in Proteus mirabilis is also concerned with the reduction of trithionate and the oxidation of sulphide. Tetrathionate is reduced to thiosulphate, thiosulphate to sulphite and sulphide, and trithionate is reduced to thiosulphate plus sulphite. The oxidation of sulphide in cell-free extracts proceeds most likely to polysulphanes or to elemental sulphur, depending on the conditions. The kinetics of the reduction of tetrathionate imply a simultaneous interaction of tetrathionate and thiosulphate on the reductase molecule. The reduction of tetrathionate is activated by thiosulphate causing a non-linear progress of this reaction. On the other hand the reduction of thiosulphate is completely blocked until tetrathionate has been depleted. The order of reduction in a mixture of thiosulphate and trithionate is imputed by the enzymatic constants of the reductase for both substrates. Therefore in cell-free extracts thiosulphate is reduced prior to trithionate and afterwards, when thiosulphate has been exhausted, trithionate and the produced thiosulphate are reduced simultaneously. Fast growing cells, however, reduce trithionate first since their intracellular redox potential is insufficiently low to permit the reduction of any thiosulphate.
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The behaviour of Campylobacter jejuni in the environment is poorly documented. Rapid loss of viability on culture media is reported. This phenomenon is associated with the development of so-called coccoid cells. It has been suggested that these cells can be infective to animals and man. Results obtained with ATP-measurements of coccoid cells and Direct Viable Count (DVC) support this hypothesis. Introduction of coccoid cells into simulated gastric, ileal and colon environments did not result in the presence of culturable cells. Oral administration to laboratory animals and volunteers caused no typical symptoms of campylobacteriosis. Until 30 days after uptake of the cells antibodies against C. jejuni could not be detected in the blood, and the presence of this microorganism in stool samples could not be demonstrated.
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A rapid method for the direct extraction of DNA from soil and sediments was developed. The indigenous microorganisms in the soil and sediments were lysed by using lysozyme and a freeze-thaw procedure. The lysate was extracted with sodium dodecyl sulfate and phenol-chloroform. In addition to a high recovery efficiency (greater than 90%), the yields of DNA were high (38 and 12 micrograms/g [wet weight] from sediments and soil, respectively). This method generated minimal shearing of the extracted DNA. The crude DNA could be further purified with an Elutip-d column if necessary. An additional advantage of this method is that only 1 g of sample is required, which allows for the analysis of small samples and the processing of many samples in a relatively short (7 h) period.
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Induction of acid resistance (habituation) in Escherichia coli at pH 5.0 took ca 5 min in broth at 37 degrees C and 30-60 min in minimal medium. Induction occurred at a range of pH values from 4.0 to 6.0; it was dependent on continuing protein and RNA synthesis but substantial acid resistance appeared in the presence of nalidixic acid. Acid resistance was long-lasting; organisms grown at pH 5.0 retained most of their resistance after 2 h growth at pH 7.0. Organisms grown at pH 5.0 showed increased synthesis of a number of cytoplasmic proteins compared with the level in cells grown at pH 7.0. DNA repair-deficient strains carrying recA, uvrA or polA1 mutations were more acid-sensitive than the repair-proficient parents but were able to habituate at pH 5.0. Organisms grown at pH 5.0 transferred the ColV plasmid much more effectively at acid pH than did those grown at pH 7.0 and habituated recipients appeared better able to repair incoming acid-damaged plasmid DNA than did those that were non-habituated. Induction of acid resistance at pH 5.0 may be significant for the survival of organisms exposed to periodic discharges of acid effluent in the aquatic environment and habituation may also allow plasmid transfer and repair of acid-damaged plasmid DNA during or after such exposure.
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To describe the spectrum of illnesses associated with Escherichia coli O157:H7 infections. Described an outbreak that showed the broad spectrum of these infections. Reviewed the clinical findings in the other eight major outbreaks reported between 1982 and 1986. Also reviewed reports of sporadic cases. Outbreaks in communities, nursing homes, a day care center, and a kindergarten. Persons identified in outbreaks of E. coli O157:H7 infections. Escherichia coli O157:H7 infection causes bloody diarrhea (hemorrhagic colitis), nonbloody diarrhea, the hemolytic uremic syndrome, and thrombotic thrombocytopenic purpura. Infection can be asymptomatic, can involve extraintestinal sites, and can be fatal. Bloody diarrhea is the commonest symptom. Most patients have severe abdominal cramps; fever is documented in less than half. Findings from fecal leukocyte examinations often suggest a noninfectious cause. Results of radiologic and colonoscopic examinations can be consistent with a diagnosis of inflammatory bowel disease or ischemic colitis. Patients at the extremes of age are at increased risk for E. coli O157:H7-associated diarrhea, the hemolytic uremic syndrome, thrombotic thrombocytopenic purpura, and death. Antimicrobial agents have not been shown to modify the illness, but there are few data on individual agents. Infection with E. coli O157:H7 should be considered in all patients with bloody diarrhea, the hemolytic uremic syndrome, or thrombotic thrombocytopenic purpura because the infection can masquerade as gastrointestinal bleeding of noninfectious cause, the antecedent diarrhea may be resolved and forgotten by the time the hemolytic uremic syndrome or thrombotic thrombocytopenic purpura is diagnosed, and the detection of E. coli O157:H7 requires specific stool culture techniques.
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Recently a great number of cases of human salmonellosis has been observed, and contaminated foods are the most important source of gastro-intestinal diseases by Salmonella. A comparative study of the efficiency of Salmonella spp. isolation from different kinds of sausage was carried out, using selenite-cystine (SC), Müller-Kauffmann tetrathionate (MK) and Rappaport-Vassiliadis (RV/43) broths. In addition, other microorganisms that produced food toxi-infections were investigated. The percentage of Salmonella detection using RV/43 broth is superior to those obtained by the MK/43 and SC/36 procedures. The first medium cited produces a higher recovery of different Salmonella strains and serotypes, and the inhibitory effects observed on the interferent competitive organisms are higher than the other broths.
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A total of 308 samples of different types were examined for the presence of salmonellas by means of three different procedures. The first consisted of pre-enrichment in buffered peptone water followed by enrichment in Rappaport-Vassiliadis medium (P/RV). The second differed only in that 1% Teepol was added to the pre-enrichment medium (PT/RV). In the third, buffered peptone water with 1% Teepol was followed by enrichment in Muller-Kauffmann tetrathionate broth also containing 1% Teepol (PT/MKT). The first of these combinations (P/RV) proved superior to the others both in terms of isolation rates and in the appearance of suspicious colonies.
A new Salmonella subspecies designated as S. choleraesuis subsp. indica (shortly, subspecies VI) was delineated on the basis of biochemical characters and genomic relatedness. Eight serovars were assigned to this subspecies: one of these was previously classified in subspecies I (serovar Ferlac) and seven in subspecies II. This subspecies can be identified by five biochemical characters: gelatinase+, malonate-, L(+)tartrate-, salicin- and sorbitol-. The type strain is CIP 102501 (serovar 1,6,14,25:a:e,n,x formerly called Ferlac).
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From 195 strains of Salmonella, 175 (89.8%) produced tetrathionate reductase (TTR). TTR-negative Salmonella were found in 7 out of 31 serotypes examined: S. paratyphi A, S. paratyphi B, S. typhimurium, S. paratyphi C, S. thompson, S. typhi, and S. enteritidis. TTR-negative S. paratyphi B and S. thompson have not previously been reported. Production of TTR is valuable for the subdivision of some Salmonella serotypes into TTR-positive and TTR-negative variants.Examination of 362 strains of Enterobacteriaceae for TTR confirmed that Escherichia coli, Shigella, Klebsiella, and Aerobacter cloacae (enterobacter) are TTR-negative, while Salmonella, Citrobacter, and Proteus are usually TTR-positive.
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We investigated two outbreaks of an unusual gastrointestinal illness that affected at least 47 people in Oregon and Michigan in February through March and May through June 1982. The illness was characterized by severe crampy abdominal pain, initially watery diarrhea followed by grossly bloody diarrhea, and little or no fever. It was associated with eating at restaurants belonging to the same fast-food restaurant chain in Oregon (P less than 0.005) and Michigan (P = 0.0005) and with eating any of three sandwiches containing three ingredients in common (beef patty, rehydrated onions, and pickles). Stool cultures did not yield previously recognized pathogens. However, a rare Escherichia coli serotype, O157:H7, that was not invasive or toxigenic by standard tests was isolated from 9 of 12 stools collected within four days of onset of illness in both outbreaks combined, and from a beef patty from a suspected lot of meat in Michigan. The only known previous isolation of this serotype was from a sporadic case of hemorrhagic colitis in 1975. This report describes a clinically distinctive gastrointestinal illness associated with E. coli O157:H7, apparently transmitted by undercooked meat.
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Three combined media ensuring the determination of 8 characteristics typical of bacteria belonging to the group Proteus-Providencia (tryptophane deamination, urease activity, production of hydrogen sulfite and indol, fermentation of mannitol, maltose, adonitol and inositol) are presented.
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Of the three primary phylogenetic domains--Archaea (archaebacteria), Bacteria (eubacteria), and Eucarya (eukaryotes)--Archaea is the least understood in terms of its diversity, physiologies, and ecological panorama. Although many species of Crenarchaeota (one of the two recognized archaeal kingdoms sensu Woese [Woese, C. R., Kandler, O. & Wheelis, M. L. (1990) Proc. Natl. Acad. Sci. USA 87, 4576-4579]) have been isolated, they constitute a relatively tight-knit cluster of lineages in phylogenetic analyses of rRNA sequences. It seemed possible that this limited diversity is merely apparent and reflects only a failure to culture organisms, not their absence. We report here phylogenetic characterization of many archaeal small subunit rRNA gene sequences obtained by polymerase chain reaction amplification of mixed population DNA extracted directly from sediment of a hot spring in Yellowstone National Park. This approach obviates the need for cultivation to identify organisms. The analyses document the existence not only of species belonging to well-characterized crenarchaeal genera or families but also of crenarchaeal species for which no close relatives have so far been found. The large number of distinct archaeal sequence types retrieved from this single hot spring was unexpected and demonstrates that Crenarchaeota is a much more diverse group than was previously suspected. The results have impact on our concepts of the phylogenetic organization of Archaea.
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The genetic relationships among 1,300 isolates of Escherichia coli representing 16 serotypes associated with enteric disease, including O157:H7 strains recovered from patients with hemorrhagic colitis and hemolytic uremic syndrome and O26:H11, O55:H6, O55:H7, O111:H2, and O128:H2 strains, many of which were isolated originally from infants with diarrhea, were estimated from allelic variation among 20 enzyme-encoding genes detected by multilocus enzyme electrophoresis. Multiple electrophoretic types were observed among isolates of each serotype, with isolates of the same O serogroup differing on average at 28% of the enzyme loci. Comparisons of the multilocus enzyme profiles revealed that 72% of the isolates belong to 15 major electrophoretic types, each of which corresponds to a bacterial clone with a wide geographic distribution. Genetically, the O157:H7 clone is most closely related to a clone of O55:H7 strains that has long been associated with worldwide outbreaks of infantile diarrhea. We propose that the new pathogen emerged when an O55:H7-like progenitor, already possessing a mechanism for adherence to intestinal cells, acquired secondary virulence factors (Shiga-like cytotoxins and plasmid-encoded adhesins) via horizontal transfer and recombination.
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Between July 1990 and April 1991 the rate of contamination with Salmonella species of poultry feeds and feed components used by the Dutch feed industry was surveyed. Ten per cent of 360, 10 g samples of poultry feeds were found to be contaminated. Mash feeds, mostly used for layer-breeders, were far more frequently (21 per cent) contaminated than pelleted feeds (1.4 per cent). The rate of contamination of 130 samples of fish meal was 31 per cent, of 83 samples of meat and bone meal 4 per cent, 58 samples of tapioca 2 per cent and of 15 samples of maize grits 27 per cent. Twenty-eight serotypes of salmonellae were isolated, but no Salmonella enteritidis was found, despite the occurrence of an epidemic in poultry caused by this serotype since 1987. The serotypes isolated most frequently were not the same as those encountered in poultry flocks. The Enterobacteriaceae isolated from the feedstuffs were predominantly thermotrophic. They were shown to be useful markers of the rate of contamination with salmonellae and of the efficiency of decontamination of the feedstuffs by pelletisation.
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A nationwide survey of veterinary laboratories culturing poultry tissue and environmental samples for Salmonella found a large variation in isolation procedures. There were 17 different selective enrichment media or combinations of enrichment media being used for poultry tissue samples. Variations were found in how long the selective enrichments were incubated and in the temperature of incubation. There were 14 different plating media being used. Many laboratories screen and identify only one colony from the plating media. For the protection of poultry breeding and hatchery organizations and with the formation of official poultry monitoring programs, with their legal and public health implications, it becomes increasingly important that diagnostic laboratories adopt minimal standardized protocols for isolating Salmonella.
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Root nodule bacteria and Escherichia coli show an adaptive acid tolerance response when grown under mildly acidic conditions. This is defined in terms of the rate of cell death upon exposure to acid shock at pH 3.0 and expressed in terms of a decimal reduction time, D. The D values varied with the strain and the pH of the culture medium. Early exponential phase cells of three strains of Rhizobium leguminosarum (WU95, 3001 and WSM710) had D values of 1, 6 and 5 min respectively when grown at pH 7.0; and D values of 5, 20 and 12 min respectively when grown at pH 5.0. Exponential phase cells of Rhizobium tropici UMR1899, Bradyrhizobium japonicum USDA110 and peanut Bradyhizobium sp. NC92 were more tolerant with D values of 31, 35 and 42 min when grown at pH 7.0; and 56, 86 and 68 min when grown at pH 5.0. Cells of E. coli UB1301 in early exponential phase at pH 7.0 had a D value of 16 min, whereas at pH 5.0 it was 76 min. Stationary phase cells of R. leguminosarum and E. coli were more tolerant (D values usually 2 to 5-fold higher) than those in exponential phase. Cells of R. leguminosarum bv. trifolii 3001 or E. coli UB1301 transferred from cultures at pH 7.0 to medium at pH 5.0 grew immediately and induced the acid tolerance response within one generation. This was prevented by the addition of chloramphenicol. Acid-adapted cells of Rhizobium leguminosarum bv. trifolii WU95 and 3001; or E. coli UB1301, M3503 and M3504 were as sensitive to UV light as those grown at neutral pH.
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Escherichia coli O157:H7 causes hemorrhagic colitis and the hemolytic uremic syndrome. In the fall of 1991, an outbreak of E coli O157:H7 infections in southeastern Massachusetts provided an opportunity to identify transmission by a seemingly unlikely vehicle. Case-control study to determine the vehicle of infection. New England cider producers were surveyed to assess production practices and determined the survival time of E coli O157:H7 organisms in apple cider. Illness was significantly associated with drinking one brand of apple cider. Thirteen (72%) of 18 patients but only 16 (33%) of 49 controls reported drinking apple cider in the week before illness began (odds ratio [OR], 8.3; 95% confidence interval [CI], 1.8 to 39.7). Among those who drank cider, 12 (92%) of 13 patients compared with two (13%) of 16 controls drank cider from cider mill A (lower 95% CI, 2.9; P < .01). This mill pressed cider in a manner similar to that used by other small cider producers: apples were not washed, cider was not pasteurized, and no preservatives were added. In the laboratory, E coli O157:H7 organisms survived for 20 days in unpreserved refrigerated apple cider. Addition of sodium benzoate 0.1% reduced survival to less than 7 days. Fresh-pressed, unpreserved apple cider can transmit E coli O157:H7 organisms, which cause severe infections. Risk of transmission can be reduced by washing and brushing apples before pressing, and preserving cider with sodium benzoate. Consumers can reduce their risk by only drinking cider made from apples that have been washed and brushed.
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This study was undertaken to determine the survivability of low-density populations (10(0) and 10(2) CFU/g) of enterohemorrhagic Escherichia coli O157:H7 inoculated into real mayonnaise and reduced-calorie mayonnaise dressing and stored at 20 and 30 degrees C, temperatures within the range used for normal commercial mayonnaise distribution and storage. Inactivation patterns at 5 degrees C and inactivation of high-inoculum populations (10(6) CFU/g) were also determined. The pathogen did not grow in either mayonnaise formulation, regardless of the inoculum level or storage temperature. Increases in storage temperature from 5 to 20 degrees C and from 20 to 30 degrees C resulted in dramatic increases in the rate of inactivation. Populations of E. coli O157:H7 in the reduced-calorie and real formulations inoculated with a population of 0.23 to 0.29 log10 CFU/g and held at 30 degrees C were reduced to undetectable levels within 1 and 2 days, respectively; viable cells were not detected after 1 day at 20 degrees C. In mayonnaise containing an initial population of 2.23 log10 CFU/g, viable cells were not detected after 4 days at 30 degrees C or 7 days at 20 degrees C; tolerance was greater in real mayonnaise than in reduced-calorie mayonnaise dressing stored at 5 degrees C. The tolerance of E. coli O157:H7 inoculated at the highest population density (6.23 log 10 CFU/g) was less in reduced-calorie mayonnaise dressing than in real mayonnaise at all storage temperatures. In reduced-calorie mayonnaise dressing and real mayonnaise initially containing 2.23 log10 CFU/g, levels were undetectable after 28 and 58 days at 5 degrees C, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
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Mapping the insertion points of 16 signature-tagged transposon mutants on the Salmonella typhimurium chromosome led to the identification of a 40-kb virulence gene cluster at minute 30.7. This locus is conserved among all other Salmonella species examined but is not present in a variety of other pathogenic bacteria or in Escherichia coli K-12. Nucleotide sequencing of a portion of this locus revealed 11 open reading frames whose predicted proteins encode components of a type III secretion system. To distinguish between this and the type III secretion system encoded by the inv/spa invasion locus known to reside on a pathogenicity island, we refer to the inv/spa locus as Salmonella pathogenicity island (SPI) 1 and the new locus as SPI2. SPI2 has a lower G+C content than that of the remainder of the Salmonella genome and is flanked by genes whose products share greater than 90% identity with those of the E. coli ydhE and pykF genes. Thus SPI2 was probably acquired horizontally by insertion into a region corresponding to that between the ydhE and pykF genes of E. coli. Virulence studies of SPI2 mutants have shown them to be attenuated by at least five orders of magnitude compared with the wild-type strain after oral or intraperitoneal inoculation of mice.
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Salmonella typhimurium periodically confronts acid environments during its life. These situations arise in chemically compromised ponds, soil, degradative cellular organelles, host digestive systems, and may even result from byproducts of their own metabolism. The levels of acid that are encountered range from mild to extreme. As a neutralophile, S. typhimurium prefers to grown in pH environments above pH 5.5. They can survive down to pH 4 for extended periods of time. However, the limits of endurance can be stretched if the organisms are first adapted to a moderate acid pH before exposing them to acidity below pH 4.0. This adaptation, called the acid-tolerance response (ATR), includes several log phase and stationary phase systems. Some of these systems are dependent on an alternate sigma factor for RNA polymerase called sigma s, whereas other systems are sigma s-independent. A key to the ATR is the synthesis of a series of acid shock inducible proteins (ASPs), 51 for log phase ATR and 15 for stationary phase ATR. Some of these ASPs require sigma s for their synthesis; others require the participation of the ferric uptake regulator protein Fur. Effective acid tolerance involves RecA-independent DNA repair systems, iron, and facets of fatty acid metabolism. Aspects of medium composition and carbon metabolism are also known to influence the nature of acid tolerance in this organism. In addition to aiding survival in the natural non-host environment, aspects of acid tolerance are also tied to virulence, as evidenced by the involvement of the mouse virulence locus mviA and the fact that acid-sensitive strains of S. typhimurium exhibit reduced virulence. This review summarizes these aspects of acid adaptation and includes a discussion of acid-regulated gene expression.