Escherichia coli O157:H7 survival, biofilm formation and acid tolerance under simulated slaughter plant moist and dry conditions

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 × 0.08 cm), 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 48 h) or 35 °C (7 or 24 h), 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 24 h at 35 °C and 48 h 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 50 ppm PAA for 45 s 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.