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Abstract: Microorganisms persisting in slaughter plant environments may develop acid resistance and be translocated to other environmental surfaces or products. The objective of this study was to evaluate the potential of Escherichia coli O157:H7 to form biofilms and maintain acid resistance, under different culture habituation scenarios, on stainless steel coupons (2×5×0.08cm), in the presence of beef carcass decontamination runoff fluids (washings). Coupons were stored in test tubes with unsterilized water washings (WW; pH 6.94) or lactic acid washings (LAW; pH 4.98), which were inoculated with E. coli O157:H7 (103–104 CFU/ml) and incubated at 15 (24 or 48h) or 35°C (7 or 24h), simulating different habituation scenarios on sites of a slaughter plant, including sanitation and overnight drying, during consecutive operational shifts. Acid resistance (AR) of planktonic and detached E. coli O157:H7 cells was assessed in tryptic soy broth adjusted to pH 3.5 with lactic acid. The highest pre-drying attachment and AR of E. coli O157:H7 were observed after 24h at 35°C and 48h at 15°C. Drying reduced (P <0.05) recovery of attached E. coli O157:H7 cells; however, exposure of dried coupons to uninoculated washings allowed recovery of attached E. coli O157:H7, which restored AR, especially under conditions that favored post-drying growth. Exposure of attached cells to 50ppm PAA for 45s before drying, as well as habituation in LAW, reduced the recovery and AR of E. coli O157:H7. Therefore, incomplete removal of biofilms may result in cells of increased AR, especially in sites within a slaughter plant, in which liquid meat wastes may remain for long periods of time. [Copyright &y& Elsevier]

Abstract: This study assessed the acid tolerance response (ATR) of stationary phase, acid-adapted (tryptic soy broth [TSB]+1% glucose) or nonacid-adapted (glucose-free TSB) Escherichia coli O157:H7 strains (ATCC43889, ATCC43895, ATCC51658 and EO139), grown individually or in a mixed culture, prior to inoculation of beef or meat decontamination runoff (washings) fluids (acidic [pH 4.95] or nonacidic [pH 7.01]). The inoculated beef was left untreated or treated by dipping for 30s in hot water (75°C) followed by 2% lactic acid (55°C). Inoculated beef samples and washings were stored aerobically at 4 or 15°C for 6d, and at set intervals (0, 2, and 6d) were exposed (for 0, 60, 120, and 180min) to pH 3.5 (adjusted with lactic acid) TSB plus 0.6% yeast extract. Overall, there were no significant () differences in responses of cultures prepared as individual or mixed strains. Decontamination of meat did not affect the subsequent ATR of E. coli O157:H7 other than resulting in lower initial pathogen levels exposed to acidic conditions. In this study, E. coli O157:H7 appeared to become more tolerant to acid following incubation in acidic washings of sublethal pH (4.89–5.22) compared to nonacidic washings (pH 6.97–7.41) at 4°C or in both types of washings incubated at 15°C. The ATR of the pathogen inoculated into washings was enhanced when cells were previously acid-adapted and incubated at 4°C. Similarly, the ATR on meat was increased by previous acid-adaptation of the inoculum in broth and enhanced by storage at 4°C. Populations on treated meat were consistently lower than those on untreated meat during storage and following exposure to acid. Although on day-0 there were no significant () differences in ATR between acid-adapted and nonacid-adapted populations on meat, acid-adapted cells displayed consistently higher resistance through day-6. This suggests that acid-adapted E. coli O157:H7 introduced on meat may become resistant to subsequent lactic acid exposure following storage at 4°C. [Copyright &y& Elsevier]

Abstract: The purpose of this work was to estimate the prevalence and concentration of Listeria monocytogenes in minced pork meat by the application of a Bayesian modeling approach. Samples (n = 100) collected from local markets were tested for L. monocytogenes using in parallel the PALCAM, ALOA and RAPID’L.mono selective media. Presence of the pathogen was confirmed through biochemical and molecular tests. Independent experiments (n = 10) for validation purposes were performed. No L. monocytogenes was enumerated by direct-plating (<10 CFU/g), though the pathogen was detected in 22% of the samples. Sensitivity and specificity varied depending on the culture method. L. monocytogenes concentration was estimated at 14–17 CFU/kg. Validation showed good agreement between observed and predicted prevalence (error = −2.17%). The use of at least two culture media in parallel enhanced the efficiency of L. monocytogenes detection. Bayesian modeling may reduce the time needed to draw conclusions regarding L. monocytogenes presence and the uncertainty of the results obtained. [Copyright &y& Elsevier]