Article

The prevalence of Clostridium botulinum in European river lamprey (Lampetra fluviatilis) in Finland

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Abstract

The prevalence of Clostridium botulinum types A, B, E and F in river lampreys caught in Finnish rivers was determined for the first time using a quantitative PCR-MPN (most probable number) analysis. One of 67 raw whole lampreys (1.5%) was positive for the botulinum neurotoxin type E gene, with the estimated C. botulinum count being 100spores/kg. Two type E strains were isolated from the positive sample and confirmed as different genotypes by pulsed-field gel electrophoresis. Although the current procedure of bringing the charcoal-broiled lampreys to market has been without any further packaging or extended storage, interest towards increasing the shelf life of the product by vacuum-packaging is increasing. Our results demonstrate that C. botulinum type E may constitute a safety hazard in processed lampreys from the Baltic Sea area if packaging and extended shelf lives are to be used. To control the potential risk, a storage temperature of 3 degrees C or below should be recommended for these products.

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... The prevalence of C. botulinum in water sediments and in fish can be influenced by various factors, such as geographical location, feeding habits of the fish species, types of samples and the detection method used. C. botulinum was found in various water sediments and fish samples (Johannsen 1962;Bott et al. 1966;Huss and Pedersen 1979;Huss 1980;Hielm et al. 1998a, b;Hyytiä et al. 1998;Fach et al. 2002;Nol et al. 2004;Merivirta et al. 2006;Leclair et al. 2012). Results of those studies have shown that the prevalence of C. botulinum, including types A, B, E, and F, in water sediment and in fish varies considerably (Table 5). ...
... The lower occurrence of C. botulinum was found in European river lamprey (Lampetra fluviatilis). Merivirta et al. (2006) reported results on the prevalence of C. botulinum in European river lamprey obtained from Finnish rivers. Lampreys (n =67) were collected from 12 rivers flowing into the Gulf of Bothnia. ...
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Fish plays an important role in the human diet, and there is an observed increase in the consumption of fish per capita in Europe. However, intensive growth of industry and agriculture may cause contamination of natural and human-made aquatic environments, and may affect not only the health of fish, but also raise safety concerns with regard to fish used for human consumption. It is well known that fish and fish products are often associated with human diseases. Thus, it is necessary to study the prevalence of pathogens in fish to ensure the safety of fish products and environments. Microbial assessment of fish also gives additional information about the hygienic status of environments, including lakes, rivers, ponds, and fish farms. Detection of pathogenic microorganisms or changes in natural microflora in the water environment could be an important indicator of possible contamination. The aim of this review was to describe and discuss the five most relevant bacterial genera and species linked to aquatic environments—Vibrio spp., Listeria monocytogenes, Yersinia spp., pathogenic Salmonella serovars, and Clostridium botulinum—causing human foodborne diseases.
... cholerae, V. vulnificus, Plesiomonas shigelloides, Edwardsiella tarda, and Streptococcus iniae), which would lead to increased use of antimicrobials [14][15][16][17][18][19][20][21][22] . However, it is not easy to determine the levels of antimicrobial usage in aquaculture as the quantum and compounds put in practice differ significantly among countries. ...
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... The disease is known to also affect birds (Doutre, 1967a;Hay et al., 1973;Forrester et al., 1980;Dohms et al., 1982;Smart et al., 1983;Wobeser et al., 1983;Shayegani et al., 1984;Okoye, 1988;Allwright et al., 1994;Woo et al., 2010;Hardy et al., 2011;Sharpe et al., 2011;Raymundo et al., 2012). There are several reports of botulism in cold blooded animals (Mengiste et al., 1990;Nol et al., 2004;Merivirta et al., 2006;Yule et al., 2006a,b;Gaunt et al., 2007;Neimanis et al., 2007;Crauste et al., 2008;King et al., 2009;Horowitz, 2010;Khoo et al., 2011). Wound botulism has been reported by several famous authors (Werner et al., 2000;Akbulut et al., 2005a,b;Schroeter et al., 2009). ...
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A risk profile for Clostrodium botulinum in pakaged seafood from the New Zeland perspective
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We describe a semi-quantitative PCR-RFLP method for detecting low densities of Cryptosporidium spp. oocysts present in final drinking water samples and natural mineral waters. UK Standard Operating Protocols were used to concentrate oocysts from drinking water samples. Oocysts were concentrated from mineral waters by membrane filtration. Cryptosporidium oocysts identified by epifluorescence microscopy on slides or filters were subjected to DNA extraction and PCR-RFLP analysis. Oocysts were disrupted by freeze-thawing in lysis buffer. Amplicons were readily detected from 2 to 5 intact oocysts on ethidium bromide stained gels following 1 round of PCR. DNA extracted from C. parvum, C. muris, C. baileyi, human-derived C. meleagridis, and C. felis were used to confirm species identity by PCR-RFLP following simultaneous digestion with DraI and VspI.
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Conference Paper
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A quantitative PCR-detection method was used to determine the presence of C. botulinum type B and E spores in eighty-seven fish representing six different species from two fish farms and ten wild freshwater whitefish. Thirty percent (29/97) of the fish were positive for C. botulinum type E with no serotype B spores being detected. The prevalence of type E in individual fish species varied from 4 % to 100 %. Fifteen type E isolates from the PCR- positive samples from one of the fish Cans were characterized by pulsed-field gel electrophoresis (PFGE), randomly amplified polymorphic DNA analysis and biochemical tests. Five different genotypes were observed, with 11 of the isolates representing a predominant clone. The discriminatory power of PFGE was superior to that of RAPD and biochemical tests. Based on these results, it was concluded that a survey of the prevalence of type E in German fishery products is indicated in order to determine the public health risk.
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The efficacy of Electrolysed Oxidising Water (EOW) for inactivating spoilage microorganisms in process water and on minimally processed vegetables was investigated. The direct effect of EOW on three important spoilage bacteria namely; Pseudomonas fluorescens, Pantoea agglomerans or Rahnella aquatilis was determined by inoculating tap water or "artificial process water" with approximately 8 log CFU/ml pure culture and electrolysing the resultant solutions. The three bacteria were each reduced to undetectable levels at low (0.5 A) and relatively higher levels (1.0 A) of current in tap water and "artificial process water". respectively. The residual effect of EOW on P fluorescens, P agglomerans or R. aquatilis was determined by incubating at room temperature 1 ml (approximately 9 log CFU/ml) pure culture suspensions in 9 ml of EOW-T (EOW produced from tap water), EOW-A (EOW produced from "artificial process water" supplemented with approximately 60.7 mg Cl-/l and 39.3 mg Na+/l) or deionised water (control) for 0, 15 45 or 90 min. The bactericidal activity of both EOW-T and EOW-A increased with the concentration of free oxidants and incubation period and the three bacteria were completely reduced at free oxidants-incubation period combinations of 3.88 mg/1-45 min and 5.1 mg/1-90 min in EOW-T and EOW-A, respectively. Two types of industrial vegetable process water; salad-mix and soup process water, which had each a total psychrotrophic count of approximately 8 log CFU/ml were then electrolysed. Without any NaCl addition, only 1.2 and 2.1 log reductions of the psychrotrophs in soup and salad-mix process water was attained respectively. Supplementation of the process water with approximately 60.7 mg Cl-/l and 39.3 mg Na+ /l afterwards resulted in complete reduction of the psychrotrophic count in both process waters, but soup process water required relatively higher levels of current compared to salad-mix water. Finally, fresh-cut lettuce was washed in EOW-T containing 3.62 mg free oxidants/l, EOW-IP (EOW produced from industrial process water) containing 2.8 mg free oxidants/l or tap water (control) for 1 or 5 min. Washine the vegetables for 1 min in EOW-T resulted in 1.9, 1.2, and 1.3 log reductions of psychrotrophs, lactic acid bacteria and Enterobacteriacae, respectively, which increased to 3.3, 2.6, and 1.9 log reductions after washing for 5 min instead. EOW-IP tested in this work had no bactericidal effect on the microflora of fresh-cut lettuce. Electrolysis could therefore be used to decontaminate process water for vegetable pre-washing and to sanitise tap water for final rinsing of vegetables, respectively. (c) 2006 Elsevier B.V. All rights reserved.
Chapter
The significance of the waterborne route of transmission for Cryptosporidium is well known and the water industry has shown high level of interest in detecting waterborne oocysts and limiting the transmission of this waterborne protozoan parasite. Determining reductions in the density of oocysts between raw and final waters can identify the treatment processes that are effective in removing oocysts. Analysis of the water catchment and raw water samples for the presence of oocysts can identify not only the contributors of waterbome oocysts, but also the likely risk of oocysts entering abstraction. The effectiveness of these procedures depends upon the ability of the analyst to identify oocysts accurately. The enhanced fluorogenic detection method can offer much required assurance to the microscopist.
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Book
Minimally processed refrigerated (MPR) fruits and vegetables are an important and rapidly developing class of MPR foods. These convenience foods are being produced by unique applications of the basic and food sciences and their supporting technologies and engineering. MPR fruits and vegetables have attracted the interest of many facets of the food industry including such diverse areas as food manufacturers, retail food stores (deli departments), restaurants, carry-out establishments, and commissary units. Much of the developmental work in this field is now being carried out in western Europe, Japan, and the United States in response to strong consumer demand, both individual and institutional, for new types of like-fresh high-quality convenience foods. The purpose of MPR foods is to deliver to the consumer a like-fresh fruit or vegetable product with an extended shelf-life and at the same time ensure food safety and maintain sound nutritional and sensory quality. MPR fruits and vegetables received their original impetus from institutional users but retail applications are gaining favor and are expected to expand rapidly.
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Bacteria that attach to surfaces aggregate in a hydrated polymeric matrix of their own synthesis to form biofilms. Formation of these sessile communities and their inherent resistance to antimicrobial agents are at the root of many persistent and chronic bacterial infections. Studies of biofilms have revealed differentiated, structured groups of cells with community properties. Recent advances in our understanding of the genetic and molecular basis of bacterial community behavior point to therapeutic targets that may provide a means for the control of biofilm infections.
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It is now recognized that the indigenous microflora of humans and animals provides protection against infections with pathogenic microorganisms. Evidence of a protective role for the intestinal flora was obtained largely from studies with either germ-free or antibiotic-treated experimental animals that are much more susceptible to infections with intestinal pathogens than are conventional animals with an intact flora.
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Micro-organisms which are subjected to non-lethal stress can exhibit significantly greater resistance when both the same or an unrelated stress is subsequently reapplied. This latter phenomenon is termed 'cross-protection' and has been shown to be mediated, at least in part, by the rpoS gene. In experiments using three strains of Escherichia coli O157:H7 one strain showed a significantly greater resistance to salt (20% w/v) when prestressed at pH 4.5 4.0 and 3.5 compared with the control (pH7.0) using lactic acid as the acidulent. The two other strains only exhibited significantly greater resistance when prestressed at pH4.5 and 4.0. Further work using only one strain showed that when prestressed at pH4.0 (only pH value tested) it exhibited a significantly greater resistance when subsequently heated at 56 degrees C for up to 80 min. Using an acid/salt stress combination the cross-protection phenomenon was shown to be induced with initial adaptation times as short as 15 min (shortest time investigated). in an experiment with rpoS mutant of E, coli O157:H7 this gene was shown to be responsible for inducing most, but not all, of the cross-protection phenomenon. This work, particularly the speed of the adaptation process, indicates the need for fundamental studies of this phenomenon to enable more accurate risk assessment to be made of food process operations. (C) 1999 Crown Copyright.
Article
Schemes for a rapid and simple identification of lactobacilli from meat and meat products are presented which also include the species only recently published (e.g. L. divergens and L. carnis), and which were verified by the investigation of 229 strains newly isolated from meat and meat products and of nine type strains.They are primarily based on differences in the fermentation of sugars and other easily determinable physiological characteristics, and therefore permit a rapid assignment of a new isolate to one of the Lactobacillus species. However, in most instances this identification has to be confirmed by determining additional characteristics (e.g. the whole range of fermented carbohydrates, types of murein etc.).
Article
A prototype immunomagnetic separation (IMS) technique was tested in five laboratories, which undertake routine analysis of water samples for Cryptosporidium oocysts, by comparing the recovery efficiency of the IMS technique with techniques in current use (the “Blue Book” Standing Committee of Analysts, SCA, method and flow cytometry, FCM). In very low turbidity samples (clean waters) of both 1ml and 10ml volumes the IMS demonstrated significantly better results than both SCA and FCM methods. Not only were higher oocyst recovery efficiencies reported but variation in recovery efficiency was reduced and fewer negative results were reported from oocyst-seeded samples than with the other two techniques. In trials with clean water or low turbidity water. FCM was the technique which moat consistently reported negative results in oocyst-seeded samples and for clean water this difference was found to be statistically significant. When the water sample was turbid the recovery efficiency of the IMS technique diminished. The results suggest that the IMS technique is affected to different extents by different material constituents in water concentrates and that FCM is apparently less affected by interfering particulate matter. Despite the potential difficulties with the IMS method with turbid water samples, the results from these trials indicate that this technique would be a very useful addition to the amsoury of methods for the concentration of oocysts from water samples and was considered by the trial participants to be simple, user-friendly and applicable to the processing of multiple samples simultaneously.
Article
Several wild lactococcal strains were tested for their ability to produce aroma compounds during growth in milk. Strains were incubated alone and in combination with Lactococcus lactis IFPL730, which is characterized by showing α-keto acid decarboxylase activity. Volatile compounds from incubated milks were analyzed by means of solid-phase microextraction (SPME) and evaluated by gas chromatography–mass spectrometry (GC–MS). Incubated milks were also sniffed for sensory analysis to describe aroma attributes. The combination of L. lactis IFPL326 that showed the highest branched chain aminotransferase activity with IFPL730 contributed to the highest formation of leucine-derived volatile compounds, such as 3-methylbutanal, 3-methyl-1-butanol and 2-hydroxy-4-methyl pentanoic acid methyl ester. In addition, the milk incubated with this combination of strains was awarded, by the test panellists, the highest scores for “ripened cheese” attribute and aroma intensity. The results indicate that combination of L. lactis strains harbouring complementary catabolic routes can contribute to improved cheese aroma formation, the combined cultures with L. lactis IFPL730 resulting in higher volatile compound formation than isolate strains.
Article
Acidic electrolyzed oxidizing (EO) water quickly kills a variety of fungi and shows promise as a broad-spectrum contact fungicide for control of foliar diseases of greenhouse-grown ornamentals. One requirement for use in the greenhouse is that EO water will not cause excessive phytotoxic symptoms on a wide variety of species. In one experiment, two applications of EO water did not damage 15 species of bedding plants. In a second experiment, EO water applied as a foliar spray three times per week for 4–7 weeks did not produce any visible phytoxicity on seven of the 12 species tested. Small, white spots were observed on flowers of geranium (Pelargonium x hortorum), impatiens (Impatiens walleriana), and vinca (Catharanthus roseus). Slight necrosis was observed on some leaf edges of petunia (Petunia x hybrida), and snapdragon (Antirrhinum majus). EO water generated from magnesium chloride produced more phytotoxicity than EO water generated by potassium chloride or sodium chloride. Phytotoxicity ratings of greater than 3 (0–10 scale) were not observed on any of the species tested. EO water caused slight damage to some plant species but, in general, appears to be safe to use as a foliar spray on a wide variety of bedding plants grown under greenhouse conditions.
Article
High performance liquid chromatography was used to analyze the principal organic acids present in wine (tartaric, malic and lactic acids) after purification of samples with Sep-Pak C18 cartridges (Waters). The method was applied to 40 samples of home-made wines from the Alpujarra-Contraviesa region of the province of Granada (Southeast Spain). These wines are considered rose, but in most cases had been subjected to unintentional maceration. The results obtained showed that the wines had not undergone complete malolactic fermentation and presented low concentrations of tartaric acid. The proportion of the concentrations of malic and lactic acids suggested a possible alteration by the undesirable development of lactic bacteria.
Article
There are three lamprey species in Finland. European river lamprey (Lampetra fluviatilis) is common along the coast of Finland and 28 rivers are known to support spawning populations while landlocked river lamprey populations exist in three watercourses. European brook lamprey (Lampetra planed) is common in freshwater all over the country, and sea lamprey (Petromyzon marinus) has been reported off the Finnish coast only 19 times since 1854. Food of the river lamprey and landlocked river lamprey includes valuable fish species such as herring, sprat, and vendace, but no effects on the fish stocks have been reported. River lamprey catch in Finnish coastal rivers make up about 2–2.5 million individuals (100 t) and lampreys are used only for human consumption. The fishing season begins in August and ends in February. Environmental changes in rivers (dams, pollution, etc.) have caused great damage to river lamprey populations. Successful attempts have been made to promote spawning by transporting lampreys over the dams. Landlocked river lamprey, brook lamprey, and sea lamprey are of no economic significance in Finland.Key words: sea lamprey, river lamprey, brook lamprey, distribution, Finland, life history, fisheries, management
Article
Lactic acid bacteria in foods have a long history of safe use. Members of the genera Lactococcus and Lactobacillus have a ‘generally-recognised-as-safe’ status, whilst members of the genera Streptococcus and Enterococcus and some other genera of lactic acid bacteria contain opportunistic pathogens. New species and more specific strains of probiotic bacteria are constantly being identified. Prior to incorporating new strains into products their efficacy should be carefully assessed and a case-by-case evaluation of whether they share the safety status of traditional food-grade organisms should be made. Genetically modified organisms are by definition always novel. Any safety assessment is based on the decision of the novel status, including phenotypic and genotypic characterisation. Additionally, for genetically modified organisms and their products, information is required in the following categories: effects of the genetic modification on the properties of the host organism, genetic stability of the genetically modified organism, specificity of expression of novel genetic material, transfer of genetic material from genetically modified organisms, and the ability of genetically modified microorganisms to colonise and to survive in the human gut.
Article
The accelerating effect exerted on proteolysis in cheese−curd slurries by the bacteriocin producer Lactococcus lactis IFPL 105, which is able to induce cell lysis in starter adjuncts with high peptidase activity, Lactobacillus casei subsp. casei IFPL731, and Lactococcus lactis subsp. lactis T1 has been studied. The optimum conditions for the use of the bacteriocin producer have been investigated to avoid late acidification by the starter and promote early cell lysis with the subsequent release of the intracellular peptidases and the acceleration of ripening without altering the cheese-making process. The induced cell lysis was of special importance in the case of Lc. lactis T1, because this strain possesses high peptidase activity and therefore can greatly influence the development of cheese flavor when added as an adjunct starter. In this study, it has been found that addition of Lc. lactis IFPL 105 does not interfere with proper acidification of the curd by the starter and increases the level of amino nitrogen correlated with early lysis of adjuncts, owing to the presence of bacteriocin. Keywords: Bacteriocin; lysis; proteolysis
Article
Numerous microbiological methods for detection or enumeration of microorganisms in food have been developped and are extensively used in routine. However, the development of international trade and the requirement for quality assurance in laboratories have stressed the need for harmonisation of these methods. Standardisation is an appropriate way to solve this isssue. It has been established at three levels: National (such as the French Association for Standardisation: Afnor), European (European Committee for Standardisation: Cen) and International (International Organisation for Standardisation: ISO). Nowadays, these organisations essentially promote horizontal standards for microbiological analyses of food and mutual recognition of standards. The definition of microbiological criteria to consider the hygienic quality of food (which is the approach of the Codex Alimentarius Committee for Food Hygiene) cannot be carried out without combining it with a given method of analysis, since the result depends considerably on the methods selected. Consequently, it is not an easy task to obtain the consensus required to establish the various standards (reference, routine or validated commercial methods). Advantages and disadvantages of standardisation depend on the type of service and the framework of analysis carried out by private or public laboratories. Standardisation simplifies technical aspects of food analysis, but also helps laboratories in quality assurance management and customer trade by defining a common language and clarifying its services. Disadvantages of standardisation reside in its rigidity and slow evolution.
Article
A method is described for acetaldehyde analysis in Streptococcus lactis cultures that involves distillation and formation of acetaldehyde 2,4-dinitrophenylhydrazone with separation by high-performance liquid chromatography (HPLC). Relative standard deviations for data obtained from HPLC analysis were slightly lower than for data obtained by a conventional spectrophotometric method for S. lactis broth cultures. Acetaldehyde recovery data were comparable for both techniques. Acetaldehyde data for two strains of S. lactis incubated at 32 °C are compared.
Article
Cl. botulinum type E is ubiquitous in Sweden and the adjacent seas. It is of terrestrial origin and is the dominant type in the Baltic's catchment area. The Baltic is thus a reservoir for type E organisms, which spread to neighbouring waters. The high frequency of type E organisms in the peel of stored potatoes may be regarded as one of the most definite indications of the terrestrial origin of this clostridium.
Article
The aim of this research was to investigate the potential relationship, if any, between the acquisition/possession of antibiotic resistance genes in strains of Salmonella and its resistance to heat stress. Chicken pieces were inoculated with antibiotic sensitive (AS) strains of S. Enteritidis and S. Typhimurium, its laboratory-acquired antibiotic-resistant (AR) mutant strains (nalidixic acid and streptomycin), or a multiresistant strain of S. Typhimurium DT104. Half of these samples were heat-shocked (48C for 30 min) and all were heat-challenged at 55C for up to 30 min. Samples were then plated on xylose lysine desoxycholate (XLD) and tryptone soya agar (TSA) overpoured with XLD. Heat-shocked cultures of S. Typhimurium DT104 had significantly higher D-values (the time required for a 1 log reduction in the number of bacteria) than their non-heat-shocked counterparts (P < 0.05). No significant differences were observed between AR and their AS. However, the D-values for S. Typhimurium DT104 were significantly higher than the D-values for S. Typhimurium (AS) and S. Enteritidis (AS) (P < 0.05). This study concluded that laboratory-acquired antibiotic-resistant mutation did not affect heat resistance of the Salmonella strains studied and suggested a potential link between multiantibiotic resistance and heat resistance in S. Typhimurium DT104.
Article
Aims: To examine factors affecting faecal shedding of the foodborne pathogens Escherichia coli O157:H7 and Salmonella in dairy cattle and evaluate antimicrobial susceptibility of these isolates. Methods: Faecal samples were obtained in replicate from lactating (LAC; n = 60) and non-lactating (NLAC; n = 60) Holstein cattle to determine influence of heat stress, parity, lactation status (LAC vs NLAC) and stage of lactation [≤60 or >60 days in milk (DIM)] and cultured for E. coli O157:H7 and Salmonella. A portion of the recovered isolates were examined for antimicrobial susceptibility using the broth microdilution technique. Results: No effects of heat stress were observed. Lactating cows shed more (P < 0·01) E. coli O157:H7 than NLAC cows (43% vs 32%, respectively). Multiparous LAC cows tended to shed more (P = 0·06) Salmonella than primiparous LAC cows (39% vs 27%, respectively). Parity did not influence (P > 0·10) bacterial shedding in NLAC cows. Cows ≤60 DIM shed more (P < 0·05) Salmonella than cows >60 DIM. Seventeen Salmonella serotypes were identified with the most prevalent being Senftenberg (18%), Newport (17%) and Anatum (15%). Seventy-nine of the Salmonella isolates were resistant to at least one of the seven antibiotics. Escherichia coli O157:H7 isolates were resistant to 11 different antibiotics with multiple resistance to nine or more antibiotics observed in five isolates. Significance and Impact of the Study: This study demonstrated differences in the shedding patterns of foodborne pathogens due to the stage of the milk production cycle and may help identify times when on-farm pathogen control would be the most effective.
Article
This study investigated the prevalence and numbers of Escherichia coli O157:H7 in minced beef and beef burgers in supermarkets and butcher shops in the Republic of Ireland. Fifteen samples were collected quarterly from each of 26 counties over a 13-month period. All samples (n=1533) were (1) directly plated on SMAC, and (2) enriched in mTSB with novobiocin, extracted by immunomagnetic separation (IMS), plating onto SMAC-CT agar and finally confirmed by PCR. Overall, E. coli O157:H7 was recovered from 43 samples (2.80%) with counts ranging from o0.52–4.03 log 10 cfu g À1 . Of the positive samples, 2.70% (32/1183) were purchased from supermarkets and 3.14% (11/350) from butcher shops. Only one product type (fresh unpacked burgers from supermarkets) was negative for E. coli O157:H7. Of the products containing the pathogen, fresh packaged burgers from supermarkets had the highest prevalence of 4.46% (7/157) while fresh unpackaged mince purchased from supermarkets had the lowest prevalence of 2.01% (6/299). Of the 43 isolates recovered, 41 possessed verotoxin-producing genes (vt1 and vt2), E. coli attaching and effacing gene (eaeA), haemolysin gene (hlyA), 60-MDa plasmid or rfb gene cluster that encodes for the biosynthesis of the O-antigen (pO157) and flagellar H7 antigen encoding gene (fliC h7). The remaining 2/43 isolates contained only one of the verotoxin-producing genes (vt1 or vt2) and all the other genes named.
Article
Three strains of Escherichia coli O157:H7 ATCC 43895, Ent C9490 and 38094 were inoculated into salami and heated in water baths at 50, 55 or 60C. At intervals between 1 and 360 min, salami samples were removed from the water bath and examined for the presence of surviving E. coli O157:H7. Samples were directly plated onto sorbitol () () MacConkey SMAC agar, and onto tryptone soya agar TSA with SMAC overlay. The number of sub-lethally damaged cells in each sample was estimated from the differences between () () the resultant direct uninjured cells only and overlay total recovery counts. In samples . heated at 50C, the percentage of cell injury ranged from 71 888% for all strains. In samples heated at 55C the percentage of sub-lethally damaged cells in strains ATCC 43895 . () and Ent C9490 was significantly higher P-0 001 at 97% than that observed in strain () 38094 64% . Cell injury was not measured at 60C. There were significant differences () between the derived decimal reduction times D-values related to the different strains of E. coli O157:H7, the heat treatment applied and the recovery ⁄enumeration agars used. . () Significant interstrain differences P-0 05 in thermotolerance were noted. Strain Ent . (C9490 was significantly more heat resistant at 50C and 60C D-values of 116 9 and .) (2 2 min, respectively , while at 55C strain 38094 was more thermotolerant D-value of .) 21 9 min . The implications of these findings for the design of studies investigating the heat resistance of E. coli O157:H7 in fermented meat environments are discussed.
Article
This study deals with the effects of yoghurt intake on wild-type and recombinant plasmid transfer from an exogenous Escherichia coli K12-derivative donor strain to an endogenous recipient strain in the digestive tract of mice associated with human faecal flora. We showed that the self-transmissible plasmid R388 was efficiently transferred to recipient strain PG1 in mice associated with human faecal flora (HFF–PG1) and that the resulting transconjugants (PG1–R388) became established at a high and maximal population level without any selective pressure. Using HFF–PG1 mice made it possible to determine whether yoghurt consumption decreases R388 transfer efficiency and the ability of transconjugant PG1–R388 to successfully colonise the digestive tract. Results indicated that yoghurt consumption had two effects: it reduced the efficacy of plasmid transfer 10-fold and decreased the transconjugant PG1–R388 population density 100-fold, compared to the control group. We also describe another HFF mouse model in which recipient PG1 was replaced by EM0 with which no plasmid transfer was observed. This model made it possible to demonstrate the potential promoting effect of yoghurt intake on transconjugant formation and establishment. Our results indicated no yoghurt effect; no transconjugants appeared in the digestive tract of HFF–EM0 mice fed on yoghurt or on standard food. In both mouse models, HFF–PG1 and HFF–EM0, yoghurt intake did not promote the mobilisation of either the non-self-transmissible plasmid pUB2380 or the recombinant plasmid pCE325.