-
[show abstract]
[hide abstract]
ABSTRACT: This study compared biofilm formation by 7 serogroups of pathogenic Escherichia coli and 2 or 3 phenotypes of Salmonella (susceptible, multidrug-resistant [MDR], and/or multidrug resistant with ampC gene [MDR-AmpC]). One-week mature biofilms were also exposed to water, quaternary ammonium compound-based (QAC), and acid-based (AB) sanitizers. Seven groups (strain mixture) of above-mentioned pathogens were separately spot-inoculated onto stainless steel coupons surfaces for target inoculation of 2 log CFU/cm(2) , then stored statically, partially submerged in 10% nonsterilized meat homogenate at 4, 15, and 25 °C. Biofilm cells were enumerated on days 0, 1, 4, and 7 following submersion in 30 mL for 1 min in water, QAC, and AB. Counts on inoculation day ranged from 1.6 ± 0.4 to 2.4 ± 0.6 log CFU/cm(2) and changed to 1.2 ± 0.8 to 1.9 ± 0.8 on day 7 at 4 °C with no appreciable difference among the 7 pathogen groups. After treatment with QAC and AB on day 7, counts were reduced (P < 0.05) to less than 0.7 ± 0.6 and 1.2 ± 0.5, respectively, with similar trends among pathogens. Biofilm formation at higher temperatures was more enhanced; E. coli O157:H7, as an example, increased (P < 0.05) from 1.4 ± 0.6 and 2.0 ± 0.3 on day 0 to 4.8 ± 0.6 and 6.5 ± 0.2 on day 7 at 15 and 25 °C, respectively. As compared to 4 °C, after sanitation, more survivors were observed for 15 and 25 °C treatments with no appreciable differences among pathogens. Overall, we observed similar patterns of growth and susceptibility to QAC and AB sanitizers of the 7 tested pathogen groups with enhanced biofilm formation capability and higher numbers of treatment survivors at higher temperatures.
Journal of Food Science 04/2013; · 1.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study evaluated growth of Listeria monocytogenes inoculated on cooked chicken meat with different marinades and survival of the pathogen as affected by microwave oven reheating. During aerobic storage at 7 °C, on days 0, 1, 2, 4, and 7, samples were reheated by microwave oven (1100 W) for 45 or 90 s and analyzed microbiologically. L. monocytogenes counts on nonmarinated (control) samples increased (P < 0.05) from 2.7 ± 0.1 (day-0) to 6.9 ± 0.1 (day-7) log CFU/g during storage. Initial (day-0) pathogen counts of marinated samples were <0.5 log CFU/g lower than those of the control, irrespective of marinating treatment. At 7 d of storage, pathogen levels on samples marinated with tomato juice were not different (P≥ 0.05; 6.9 ± 0.1 log CFU/g) from those of the control, whereas for samples treated with the remaining marinades, pathogen counts were 0.7 (soy sauce) to 2.0 (lemon juice) log CFU/g lower (P < 0.05) than those of the control. Microwave oven reheating reduced L. monocytogenes counts by 1.9 to 4.1 (45 s) and >2.4 to 5.0 (90 s) log CFU/g. With similar trends across different marinates, the high levels of L. monocytogenes survivors found after microwave reheating, especially after storage for more than 2 d, indicate that length of storage and reheating time need to be considered for safe consumption of leftover cooked chicken.
Journal of Food Science 01/2013; · 1.66 Impact Factor
-
Journal of food protection 01/2013; 76(1):4-5. · 1.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Studies were conducted to compare the decontamination efficacy of six chemical treatments against Escherichia coli O157:H7 and multidrug-resistant and antibiotic-susceptible Salmonella inoculated on beef trimmings. The inocula, comprising four-strain mixtures of rifampin-resistant E. coli O157:H7 and antibiotic-susceptible or multidrug-resistant (MDR and/or MDR-AmpC) Salmonella Newport and Salmonella Typhimurium, were inoculated (3 log CFU/cm(2)) separately onto samples (10 by 5 by 1 cm) derived from beef chuck rolls. Samples were left untreated (control), were immersed for 30 s in acidified sodium chlorite (0.1%, pH 2.5), peroxyacetic acid (0.02%, pH 3.8), sodium metasilicate (4%, pH 12.6), Bromitize Plus (0.0225% active bromine, pH 6.6), or AFTEC 3000 (pH 1.2), or were immersed for 5 s in SYNTRx 3300 (pH 1.0). Levels of surviving Salmonella on treated trimmings were not influenced by serotype or antibiotic resistance phenotype and were generally similar (P ≥ 0.05) or lower (P < 0.05) than levels of surviving E. coli O157:H7 regardless of antimicrobial treatment. Overall, depending on chemical treatment (reductions within each chemical treatment were similar among all tested inocula), initial counts of E. coli O157:H7 (2.7 to 3.1 log CFU/cm(2)) were reduced (P < 0.05) by 0.2 to 1.4 log CFU/cm(2). Similarly, initial counts of the tested Salmonella inocula (2.8 to 3.3 log CFU/cm(2)) were reduced (P < 0.05) by 0.4 to 1.4 (Salmonella Newport, antibiotic susceptible), 0.3 to 1.4 (Salmonella Newport, MDR-AmpC), 0.2 to 1.5 (Salmonella Typhimurium, antibiotic susceptible), 0.4 to 1.3 (Salmonella Typhimurium, MDR), and 0.4 to 1.5 (Salmonella Typhimurium, MDR-AmpC) log CFU/cm(2), depending on antimicrobial treatment. Reductions obtained with sodium metasilicate were 1.3 to 1.5 log CFU/cm(2), regardless of inoculum, and reductions obtained with the five remaining antimicrobial treatments were 0.2 to 0.7 log CFU/cm(2) (depending on treatment). Findings of this study should be useful to regulatory authorities and the meat industry as they consider Salmonella contamination on beef trimmings.
Journal of food protection 11/2012; 75(11):1960-7. · 1.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Studies were performed to determine whether lactic acid treatments used to reduce Escherichia coli O157:H7 on beef trimmings are also effective in controlling non-O157 Shiga toxin-producing E. coli (nSTEC), and multidrug-resistant and antibiotic-susceptible Salmonella. Beef trimming pieces (10 by 5 by 1 cm) were inoculated (3 log CFU/cm(2)) separately with four-strain mixtures of rifampin-resistant E. coli O157:H7, O26, O45, O103, O111, O121, and O145. Similarly, in a second study, trimmings were separately inoculated with rifampin-resistant E. coli O157:H7, and antibiotic-susceptible or multidrug-resistant (MDR and/or MDR-AmpC) Salmonella Newport and Salmonella Typhimurium. Inoculated trimmings were left untreated (control) or were immersed for 30 s in 5% lactic acid solutions (25 or 55°C). No differences (P ≥ 0.05) were obtained among surviving counts of E. coli O157:H7 and those of the tested nSTEC serogroups on lactic acid-treated (25 or 55°C) samples. Counts (3.1 to 3.3 log CFU/cm(2)) of E. coli O157:H7 and nSTEC were reduced (P < 0.05) by 0.5 to 0.9 (25°C lactic acid) and 1.0 to 1.4 (55°C lactic acid) log CFU/cm(2). Surviving counts of Salmonella on treated trimmings were not influenced by serotype or antibiotic resistance phenotype and were similar (P ≥ 0.05) or lower (P < 0.05) than surviving counts of E. coli O157:H7. Counts (3.0 to 3.3 log CFU/cm(2)) were reduced (P < 0.05) by 0.5 to 0.8 (E. coli O157:H7) and 1.3 to 1.5 (Salmonella) log CFU/cm(2) after treatment of samples with 25°C lactic acid. Corresponding reductions following treatment with lactic acid at 55°C were 1.2 to 1.5 (E. coli O157:H7) and 1.6 to 1.9 (Salmonella) log CFU/cm(2). Overall, the results indicated that lactic acid treatments used against E. coli O157:H7 on beef trimmings should be similarly or more effective against the six nSTEC serogroups and against multidrug-resistant and antibiotic-susceptible Salmonella Newport and Salmonella Typhimurium.
Journal of food protection 10/2012; 75(10):1751-8. · 1.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The decontamination efficacy of 6 chemical treatments for beef trimmings were evaluated against Escherichia coli O157:H7 and 6 non-O157 Shiga toxin-producing E. coli (nSTEC) serogroups. Rifampicin-resistant 4-strain mixtures of E. coli O157:H7 and nSTEC serogroups O26, O45, O103, O111, O121, and O145 were separately inoculated (3 to 4 log CFU/cm(2) ) onto trimmings (10 × 5 × 1 cm; approximately 100 g) fabricated from beef chuck rolls, and were immersed for 30 s in solutions of acidified sodium chlorite (0.1%, pH 2.5), peroxyacetic acid (0.02%, pH 3.8), sodium metasilicate (4%, pH 12.5), Bromitize(®) Plus (0.0225% active bromine, pH 6.6), or AFTEC 3000 (pH 1.2), or for 5 s in SYNTRx 3300 (pH 1.0). Each antimicrobial was tested independently together with an untreated control. Results showed that all tested decontamination treatments were similarly effective against the 6 nSTEC serogroups as they were against E. coli O157:H7. Irrespective of pathogen inoculum, treatment of beef trimmings with acidified sodium chlorite, peroxyacetic acid, or sodium metasilicate effectively (P < 0.05) reduced initial pathogen counts (3.4 to 3.9 log CFU/cm(2) ) by 0.7 to 1.0, 0.6 to 1.0, and 1.3 to 1.5 log CFU/cm(2) , respectively. Reductions of pathogen counts (3.1 to 3.2 log CFU/cm(2) ) by Bromitize Plus, AFTEC 3000, and SYNTRx 3300 were 0.1 to 0.4 log CFU/cm(2) , depending on treatment. Findings of this study should be useful to regulatory authorities and the meat industry as they consider nSTEC contamination in beef trimmings. Practical Applications: Findings of this study should be useful to: (i) meat processors as they design and conduct studies to validate the efficacy of antimicrobial treatments to control pathogen contamination on fresh beef products; and (ii) regulatory agencies as they consider approaches for better control of the studied pathogens.
Journal of Food Science 08/2012; 77(9):M539-44. · 1.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The acid resistance of Listeria monocytogenes was evaluated: (i) after short (shock) or long-term (adaptation during growth) exposure to reduced (5.5) or neutral (7.2) pH in a liquid (broth) medium or on a solid surface (agar), and (ii) after growth on the surface of ham and turkey slices or in homogenates of these products. Three L. monocytogenes strains (serotypes 1/2a, 1/2b and 4b) were individually inoculated at: (i) 10(4)-10(5)CFU/ml in tryptic soy broth with 0.6% yeast extract (TSBYE) or on tryptic soy agar with 0.6% yeast extract (TSAYE) at pH 7.2 with 1% (+G) or without (-G) glucose of or TSBYE and TSAYE with 0.25% glucose at pH 5.5 (lactic acid) and incubated at 20°C, and (ii) 10(2)-10(3)CFU/cm(2) on ham and turkey slices (pH 6.39-6.42; formulated with potassium lactate and sodium diacetate) or in their homogenates (1:4 and 1:9; representing viscous [slurry] and liquid residues [purge], respectively), and stored at 10°C. The acid resistance of each strain was assessed in TSBYE of pH 3.5 (lactic acid) for strains growing in broth or on agar surfaces, and in TSBYE of pH 1.5 (HCl) for strains growing on ham and turkey slices or in their homogenates. Habituation at pH 5.5 for 3 or 24h at 20°C increased acid (pH 3.5) resistance of all strains compared to the control (pH 7.2). Cells grown on the surface of TSAYE-G (pH 7.2 or 5.5) showed higher resistance than cells grown in broth (TSBYE-G), whereas the opposite was observed for cells grown on TSAYE + G or in TSBYE + G. Growth of L. monocytogenes on meat product slices was markedly slower than in homogenates. Pathogen reductions following exposure to pH 1.5, after 10 and 27days of storage were strain-dependent and in the ranges of 0.5-2.5, 1.3-4.5 and 4.0-7.6 log units for cells grown on product slices in 1:4 and 1:9 homogenates, respectively. The results suggest that L. monocytogenes cells growing on food surfaces or in viscous matrices may show higher resistance to lethal acid conditions than cells growing in liquid substrates.
International journal of food microbiology 08/2012; 159(2):160-6. · 3.01 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Surface-browned but uncooked frozen breaded chicken products have been associated with salmonellosis outbreaks due to inadequate or no cooking of the products before consumption. This study was conducted to evaluate the effect of three antimicrobials against Salmonella during manufacture of a surface-browned, uncooked frozen breaded chicken meat product. Fresh chicken breast meat portions (5 by 5 by 5 cm) were inoculated (4 to 5 log CFU/g) with Salmonella and mixed with caprylic acid (CAA; 0.5 and 1.0%), carvacrol (CAR; 0.3 and 0.5%), ε-polylysine (POL; 0.125 and 0.25%), or distilled water (control). Sodium chloride (1.2%) and sodium tripolyphosphate (0.3%) were added to all treatments, and the mixtures were ground (5% total moisture enhancement level) and formed into portions (9 by 5 by 3 cm). The products were breaded and surface browned by baking in an oven (208°C for 15 min) or deep frying in vegetable oil (190°C for 15 s), packaged in polyethylene bags, and stored at -20°C for 7 days. Total reductions of inoculated Salmonella in untreated control oven- or fryer-browned products after frozen storage were 1.2 and 0.8 log CFU/g, respectively. In comparison, treatment with CAA, CAR, or POL reduced initial pathogen counts by 3.3 to >4.5, 4.1 to >4.7, and 1.1 to 1.6 log CFU/g, respectively, regardless of the antimicrobial concentration and browning method. Treatment with 1.0% CAA (oven browned) or 0.5% CAR (oven or fryer browned) reduced Salmonella to nondetectable levels (<0.3 log CFU/g) in stored frozen products. These data may be useful for development of suitable antimicrobial treatments to reduce the risk of Salmonella contamination in surface-browned, uncooked frozen breaded chicken products.
Journal of food protection 06/2012; 75(6):1023-8. · 1.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Caprylic acid (CAA), carvacrol (CAR), ε-polylysine (POL), and their combinations were evaluated for reduction of Salmonella contamination in not-ready-to-eat surface-browned, frozen, breaded chicken products. Fresh chicken breast meat pieces (5 × 5 × 5 cm) were inoculated with Salmonella (7-strain mixture; 4-5 log CFU/g) and mixed with distilled water (control) or with CAA, CAR, and POL as single or combination treatments of 2 or 3 ingredients. Sodium chloride (1.2%) and sodium tripolyphosphate (0.3%) were added to all formulations, followed by grinding of the mixtures and forming into 9 × 5 × 3 cm portions. Sample surfaces were brushed with egg whites, coated with breadcrumbs, surface-browned in an oven (208 °C, 15 min), packaged, and stored at -20 °C (7 d). Total reductions of inoculated Salmonella in untreated (control) surface-browned, breaded products after frozen storage were 0.8 to 1.4 log CFU/g. In comparison, single treatments of CAA (0.25% to 1.0%), CAR (0.3% to 0.5%), and POL (0.125% to 1.0%) reduced counts by 2.9 to at least 4.5, 3.4 to at least 4.4, and 1.4 to 2.3 log CFU/g, respectively, depending on concentration. Pathogen counts of products treated with 2- or 3-ingredient combination treatments (0.03125% to 0.25% CAA, 0.0375% to 0.3% CAR, and/or 0.5% POL) were 0.4 to at least 3.3 log CFU/g lower (depending on treatment) than those of the untreated controls. The antimicrobial activity of 2-ingredient combinations comprised of 0.125% CAA, 0.15% CAR, or 0.5% POL was enhanced (P < 0.05) when applied as a 3-ingredient combination (that is, 0.125% CAA + 0.15% CAR + 0.5% POL). These data may be useful for the selection of antimicrobial treatments to reduce Salmonella contamination in not-ready-to-eat processed chicken products. PRACTICAL APPLICATION: Findings from the study may be useful for the selection of suitable antimicrobials, concentrations, and combinations to reduce Salmonella contamination in not-ready-to-eat surface-browned, frozen, breaded chicken products.
Journal of Food Science 06/2012; 77(7):M405-11. · 1.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Studies examined the effects of meat-contact material types, inoculation substrate, presence of air at the liquid-solid surface interface during incubation, and incubation substrate on the attachment/transfer and subsequent biofilm formation by Escherichia coli O157:H7 on beef carcass fabrication surface materials. Materials studied as 2 × 5 cm coupons included stainless steel, acetal, polypropylene, and high-density polyethylene. A 6-strain rifampicin-resistant E. coli O157:H7 composite was used to inoculate (6 log CFU/mL, g, or cm²) tryptic soy broth (TSB), beef fat/lean tissue homogenate (FLH), conveyor belt-runoff fluids, ground beef, or beef fat. Coupons of each material were submerged (4 °C, 30 min) in the inoculated fluids or ground beef, or placed between 2 pieces of inoculated beef fat with pressure (20 kg) applied. Attachment/transfer of the pathogen was surface material and substrate dependent, although beef fat appeared to negate differences among surface materials. Beef fat was the most effective (P < 0.05) inoculation substrate, followed by ground beef, FLH, and TSB. Incubation (15 °C, 16 d) of beef fat-inoculated coupons in a beef fat homogenate (pH 4.21) allowed the pathogen to survive and grow on coupon surfaces, with maximal biofilm formation observed between 2 and 8 d of storage and when air was present at the liquid-solid interface. The results indicated that the process of fabricating beef carcasses may be conducive to the attachment of E. coli O157:H7 onto meat-contact surfaces and subsequent biofilm formation. Furthermore, it is recommended that substrates found in beef fabrication settings, rather than laboratory culture media, be used in studies designed to investigate E. coli O157:H7 biofilm development and control in these environments. PRACTICAL APPLICATION: Findings of this study provide knowledge on the effect of type of beef carcass fabrication surface material, fabrication-floor fluids and residues, and incubation conditions on attachment/transfer and subsequent biofilm formation by E. coli O157:H7. The results highlight the importance of thoroughly cleaning soiled surfaces to remove all remnants of beef fat or other organic material that may harbor or protect microbial contaminants during otherwise lethal antimicrobial interventions.
Journal of Food Science 05/2012; 77(6):M343-7. · 1.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Studies evaluated thermal inactivation of Escherichia coli O157:H7 inoculated at different depths of simulated blade-tenderized non-intact steaks. Fresh beef slices (0.3 or 0.6 cm thick) were stacked on top of each other to form 2.4 or 1.2 cm thick steaks. Steaks were blade-tenderized and then inoculated with rifampicin-resistant Escherichia coli O157:H7 (8 strain mixture; 4 log CFU/cm(2)) on the surface or between slices, vacuum-packaged, and stored at 4 or -20 °C for 5 d before cooking. Steaks were cooked by pan-broiling or roasting to a geometric center temperature of 60 °C. Frozen samples were either cooked from the frozen state or after thawing to approximately 4 or 25 °C. In steaks inoculated on the external surface and cooked by pan-broiling, pathogen survivors recovered from thinner (1.2 cm) steaks were greater (P < 0.05) than those recovered from thicker (2.4 cm) steaks. Cooking steaks from a frozen state or after thawing (4 or 25 °C) did not (P ≥ 0.05) affect extent of pathogen inactivation. Survivors after pan-broiling of 2.4 cm thick steaks increased (P < 0.05) from 0.3 to 1.3 log CFU/cm(2) for surface-inoculated steaks to 2.5 to 3.2 log CFU/cm(2) for samples inoculated at the center (1.2 cm depth). In comparison, overall thermal destruction of the pathogen in steaks cooked by roasting was less, and survivor counts were generally not different (P ≥ 0.05) at each depth of inoculation. These data should be useful in development of lethality guidelines to ensure safe consumption of non-intact meat products. PRACTICAL APPLICATION: Results of this study should be useful for developing cooking guidelines, for foodservice establishments and consumers, to ensure safe consumption of non-intact meat products.
Journal of Food Science 02/2012; 77(2):M108-14. · 1.66 Impact Factor
-
Journal of food protection 01/2012; 75(1):4-5. · 1.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Escherichia coli O157:H7 attached to beef-contact surfaces found in beef fabrication facilities may serve as a source of cross-contamination. This study evaluated E. coli O157:H7 attachment, survival and growth on food-contact surfaces under simulated beef processing conditions. Stainless steel and high-density polyethylene surfaces (2×5cm) were individually suspended into each of three substrates inoculated (6log CFU/ml or g) with E. coli O157:H7 (rifampicin-resistant, six-strain composite) and then incubated (168h) statically at 4 or 15°C. The three tested soiling substrates included sterile tryptic soy broth (TSB), unsterilized beef fat-lean tissue (1:1 [wt/wt]) homogenate (10% [wt/wt] with sterile distilled water) and unsterilized ground beef. Initial adherence/attachment of E. coli O157:H7 (0.9 to 2.9log CFU/cm(2)) on stainless steel and high-density polyethylene was not affected by the type of food-contact surface but was greater (p<0.05) through ground beef. Adherent and suspended E. coli O157:H7 counts increased during storage at 15°C (168h) by 2.2 to 5.4log CFU/cm(2) and 1.0 to 2.8log CFU/ml or g, respectively. At 4°C (168h), although pathogen levels decreased slightly in the substrates, numbers of adherent cells remained constant on coupons in ground beef (2.4 to 2.5log CFU/cm(2)) and increased on coupons in TSB and fat-lean tissue homogenate by 0.9 to 1.0and 1.7 to 2.0log CFU/cm(2), respectively, suggesting further cell attachment. The results of this study indicate that E. coli O157:H7 attachment to beef-contact surfaces was influenced by the type of soiling substrate and temperature. Notably, attachment occurred not only at a temperature representative of beef fabrication areas during non-production hours (15°C), but also during cold storage (4°C) temperatures, thus, rendering the design of more effective sanitation programs necessary.
International journal of food microbiology 10/2011; 149(3):262-8. · 3.01 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Brine solution injection of beef contaminated with Escherichia coli O157:H7 on its surface may lead to internalization of pathogen cells and/or cross-contamination of the brine, which when recirculated, may serve as a source of new product contamination. This study evaluated survival of E. coli O157:H7 in brines formulated without or with antimicrobials. The brines were formulated in sterile distilled water (simulating the composition of freshly prepared brines) or in a nonsterile 3% meat homogenate (simulating the composition of recirculating brines) at concentrations used to moisture-enhance meat to 110% of initial weight, as follows: sodium chloride (NaCl, 5.5%) + sodium tripolyphosphate (STP, 2.75%), NaCl + sodium pyrophosphate (2.75%), or NaCl + STP combined with potassium lactate (PL, 22%), sodium diacetate (SD, 1.65%), PL + SD, lactic acid (3.3%), acetic acid (3.3%), citric acid (3.3%), nisin (0.0165%) + ethylenediamine tetraacetic acid (EDTA, 200 mM), pediocin (11000 AU/mL) + EDTA, sodium metasilicate (2.2%), cetylpyridinium chloride (CPC, 5.5%), or hops beta acids (0.0055%). The brines were inoculated (3 to 4 log CFU/mL) with rifampicin-resistant E. coli O157:H7 (8-strain composite) and stored at 4 or 15 °C (24 to 48 h). Immediate (0 h) pathogen reductions (P < 0.05) of 1.8 to ≥ 2.4 log CFU/mL were observed in brines containing CPC or sodium metasilicate. Furthermore, brines formulated with lactic acid, acetic acid, citric acid, nisin + EDTA, pediocin + EDTA, CPC, sodium metasilicate, or hops beta acids had reductions (P < 0.05) in pathogen levels during storage; however, the extent of pathogen reduction (0.4 to > 2.4 log CFU/mL) depended on the antimicrobial, brine type, and storage temperature and time. These data should be useful in development or improvement of brine formulations for control of E. coli O157:H7 in moisture-enhanced meat products. PRACTICAL APPLICATION: Results of this study should be useful to the meat industry for developing or modifying brine formulations to reduce the risk of E. coli O157:H7 in moisture-enhanced meat products.
Journal of Food Science 08/2011; 76(7):M478-85. · 1.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study developed growth/no growth models for predicting growth boundaries of Listeria monocytogenes on ready-to-eat cured ham and uncured turkey breast slices as a function of lactic acid concentration (0% to 4%), dipping time (0 to 4 min), and storage temperature (4 to 10 °C). A 10-strain composite of L. monocytogenes was inoculated (2 to 3 log CFU/cm²) on slices, followed by dipping into lactic acid and storage in vacuum packages for up to 30 d. Total bacterial (tryptic soy agar plus 0.6% yeast extract) and L. monocytogenes (PALCAM agar) populations were determined on day 0 and at the endpoint of storage. The combinations of parameters that allowed increases in cell counts of L. monocytogenes of at least l log CFU/cm² were assigned the value of 1, while those limiting growth to <1 log CFU/cm² were given the value of 0. The binary data were used in logistic regression analysis for development of models to predict boundaries between growth and no growth of the pathogen at desired probabilities. Indices of model performance and validation with limited available data indicated that the models developed had acceptable goodness of fit. Thus, the described procedures using bacterial growth data from studies with food products may be appropriate in developing growth/no growth models to predict growth and to select lactic acid concentrations and dipping times for control of L. monocytogenes. PRACTICAL APPLICATION: The models developed in this study may be useful in selecting lactic acid concentrations and dipping times to control growth of Listeria monocytogenes on cured ham and uncured turkey breast during product storage, and in determining probabilities of growth under selected conditions. The modeling procedures followed may also be used for application in model development for other products, conditions, or pathogens.
Journal of Food Science 08/2011; 76(6):M450-5. · 1.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study was conducted to compare thermal inactivation of stress-adapted and nonadapted Escherichia coli O157:H7 in nonintact beef moisture enhanced with different brine formulations and cooked to 65°C. Coarsely ground beef was mixed with acid, cold, heat, starvation, or desiccation stress-adapted or nonadapted rifampin-resistant E. coli O157:H7 (eight-strain mixture, 5 to 6 log CFU/g) and a brine solution for a total moisture enhancement level of 10%. The brine treatments included distilled water (control), sodium chloride (0.5% NaCl) plus sodium tripolyphosphate (0.25% STP), or NaCl + STP combined with cetylpyridinium chloride (0.2% CPC), lactic acid (0.3% LA), or sodium metasilicate (0.2% SM). The treated meat was extruded into bags (15 cm diameter), semifrozen (-20°C for 4.5 h), and cut into 2.54-cm (1-in.)-thick portions. Samples were individually vacuum packaged, frozen (-20°C for 42 h), and tempered at 4°C for 2.5 h before cooking. Partially thawed (-1.8 ± 0.4°C) samples were pan broiled to an internal temperature of 65°C. Pathogen counts of partially thawed (before cooking) samples moisture enhanced with brines containing CPC, LA, or SM were 0.7 to 1.1, 0.0 to 0.4, and 0.2 to 0.4 log CFU/g, respectively, lower than those of the control. Compared with microbial count reductions obtained after pan broiling of beef inoculated with nonadapted E. coli O157:H7 cells, count reductions during cooking of meat inoculated with cold and desiccation stress-adapted, acid stress-adapted, and heat and starvation stress-adapted cells indicated sensitization, cross protection, and no effect, respectively, of these stresses on the pathogen during subsequent exposure to heat. Among all stressed cultures, CPC-treated samples (0.8 to 3.6 log CFU/g) and LA-treated samples (0.8 to 3.5 log CFU/g) had the lowest numbers of E. coli O157:H7 survivors after cooking.
Journal of food protection 04/2011; 74(4):531-8. · 1.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A longitudinal study was conducted to track Listeria contamination patterns in ready-to-eat meats from six small or very small meat processing plants located in three states over 1 year. A total of 688 environmental sponge samples were collected from nonfood contact surfaces during bimonthly visits to each plant. Overall, L. monocytogenes was isolated from 42 (6.1%) environmental samples, and its prevalence ranged from 1.7 to 10.8% across different plants. Listeria spp., other than L. monocytogenes, were isolated from 9.5% of samples overall, with the prevalence ranging from 1.5 to 18.3% across different plants. The prevalence of L. monocytogenes correlated well with that of other Listeria spp. for some but not all plants. One L. monocytogenes isolate representing each positive sample was characterized by molecular serotyping, EcoRI ribotyping, and pulsed-field gel electrophoresis typing. Seven sample sites tested positive for L. monocytogenes on more than one occasion, and the same ribotype was detected more than once at five of these sites. Partial sigB sequencing was used to speciate other Listeria spp. isolates and assign an allelic type to each isolate. Other Listeria spp. were isolated more than once from 14 sample sites, and the same sigB allelic type was recovered at least twice from seven of these sites. One plant was colonized by an atypical hemolytic L. innocua strain. Our findings indicate that small and very small meat processing plants that produce ready-to-eat meat products are characterized by a varied prevalence of Listeria, inconsistent correlation between contamination by L. monocytogenes and other Listeria spp., and a unique Listeria molecular ecology.
Journal of food protection 01/2011; 74(1):63-77. · 1.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study assessed the distribution of class 1 integrons in commensal bacteria isolated from agricultural and nonfarm environments, and the transferability of class 1 integrons to pathogenic bacteria. A total of 26 class 1 integron-positive isolates were detected in fecal samples from cattle operations and a city park, water samples from a beef ranch and city lakes, and soil, feed (unused), manure, and compost samples from a dairy farm. Antimicrobial susceptibility testing of class 1 integron-positive Enterobacteriaceae isolates from city locations displayed multi-resistance to 12-13 out of the 22 antibiotics tested, whereas class 1 integron-positive Enterobacteriaceae isolates from cattle operations only displayed tetracycline resistance. Most class 1 integrons had one gene cassette belonging to the aadA family that confers resistance to streptomycin and spectinomycin. One isolate from a dog fecal sample collected from a city dog park transferred its class 1 integron to a strain of Escherichia coli O157:H7 at a frequency of 10(-7) transconjugants/donor by in vitro filter mating experiments under the stated laboratory conditions. Due to the numerous factors that may affect the transferability testing, further investigation using different methodologies may be helpful to reveal the transferability of the integrons from other isolates. The presence of class 1 integrons among diverse commensal bacteria from agricultural and nonfarm environments strengthens the possible role of environmental commensals in serving as reservoirs of antibiotic resistance genes.
Foodborne Pathogens and Disease 12/2010; 7(12):1441-51. · 2.26 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study examined the presence of antibiotic-resistant commensal bacteria among cattle operations representing areas heavily affected by agriculture, city locations representing areas affected by urban activities and indirectly affected by agriculture, and a national park representing an area not affected by agriculture. A total of 288 soil, fecal floor, and water samples were collected from cattle operations, from the city of Fort Collins, and from Rocky Mountain National Park (RMNP) in Colorado. In addition, a total of 42 new and unused feed, unused bedding, compost, and manure samples were obtained from the cattle operations. Total, tetracycline-resistant, and ceftiofur-resistant bacterial populations were enumerated by both standard culture plating and real-time PCR methods. Only wastewater samples from the cattle operations demonstrated both higher tetracycline-resistant bacterial counts (enumerated by the culture plating method) and tetracycline resistance gene copies (quantified by real-time PCR) compared to water samples collected from non-farm environments. The ceftiofur resistance gene, blaCMY-2, was not detectable in any of the samples, while the tetracycline resistance genes examined in this study, tet(B), tet(C), tet(W), and tet(O), were detected in all types of tested samples, except soil samples from RMNP. Tetracycline resistance gene pools quantified from the tet(O) and tet(W) genes were bigger than those from the tet(B) and tet(C) genes in fecal and water samples. Although only limited resistance genes, instead of a full set, were selected for real-time PCR quantification in this study, our results point to the need for further studies to determine natural and urban impacts on antibiotic resistance.
Canadian Journal of Microbiology 09/2010; 56(9):761-70. · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: United States regulations require ready-to-eat meat and poultry processors to control Listeria monocytogenes using interventions which may include antimicrobials that reduce post-processing contamination by at least 1 log-cycle; if the treatment achieves > or = 2 log reductions, the plant is subject to less frequent microbial testing. Lactic acid (LA) may be useful as a post-lethality intervention and its antimicrobial properties may increase with temperature of application. The aim of this study was to evaluate the effect of LA solution concentration and temperature on L. monocytogenes counts of inoculated frankfurters and to identify parameters (concentration, temperature, and time) that achieve 1 and 2 log-unit immediate reductions. Frankfurters were surface-inoculated with a 10-strain mixture of L. monocytogenes (4.4 +/- 0.1 log CFU/cm(2)) and then immersed in distilled water or LA solutions (0-3%) of 4, 25, 40, or 55 degrees C for 0-120 s. A regression equation for L. monocytogenes reduction included significant (P < 0.05) effects by the terms of concentration, time, temperature, and the interaction of concentration and temperature; other tested parameters (other interactions, quadratic and cubic terms), within the experimental range examined, did not affect (P > or = 0.05) the extent of reduction. Results indicated that the effectiveness of LA against L. monocytogenes, in addition to concentration, increased with solution temperature (in the range of 0.6-2.8 log CFU/cm(2)). The developed equation may allow processors to vary conditions of treatment with LA to achieve a 1 or 2 log-unit reduction of the pathogen and comply with United States regulations.
Food Microbiology 09/2010; 27(6):783-90. · 3.28 Impact Factor
