Survival and stress response of escherichia coli O157:H7 exposed to alkaline cleaners
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Studies were undertaken to evaluate the effects of alkaline cleaners commonly used in food processing environments on survival and stress responses of the foodborne pathogen Escherichia coli O157:H7. Alkaline cleaners containing either sodium hydroxide or potassium hydroxide and hypochlorite had greater bactericidal activity against cells of wild-type and rpoSdeficient strains of E. coli O157:H7 than those did not contain these ingredients. Populations of cells of both strains in stationary growth phase were not more susceptible than those in logarithmic phase. Cells exposed to an alkaline cleaner containing sodium hydroxide and hypochlorite followed by heat treatment showed greater thermotolerance than cells exposed to alkaline cleaners not containing hydroxide or hypochlorite. No cross protection was observed in either strain of E. coli O157:H7 exposed to alkaline cleaners and subsequent sanitizers. Cells exposed to alkaline cleaner followed by inoculation into roast beef and salami and stored at various temperatures were not cross protected against acid or cold stress. Both wild type and rpoS deficient cells resuscitated and grew in roast beef held at 12oC but not in salami held at 12 or 20oC. The rpoS gene may play a role in protecting cells from heat after exposure to an alkaline cleaner at 12oC, and may also aid in the resuscitation of cells in roast beef stored at 12oC. Populations of wild type and rpoS-deficient cells in biofilms formed on stainless steel were susceptible to killing by an alkaline cleaner but not by bacteriophage specific for E. coli O157:H7. The effectiveness of alkaline cleaners in killing E. coli O157:H7 in suspension and in biofilms is attributed to a synergistic bactericidal mechanism caused by high pH and hypochlorite. This research provides insight into the behavior of cells of E. coli O157:H7 exposed to alkaline cleaners and sanitizers in food processing and food service environments.