EFFECT OF ACID ADAPTATION ON THERMAL TOLERANCE OF ESCHERICHIA COLI O157:H7 AND SALMONELLA ENTERICA IN MEAT SERUM

Abstract

ABSTRACTEscherichia coli O157:H7 and Salmonella were adapted to acidic environments by growing in tryptic soy broth with 1% glucose (TSB + 1%G). Thermal tolerance of acid‐adapted pathogens was evaluated in meat serum. Five‐strain cocktail of both bacteria were grown separately in TSB and TSB + 1%G for 24 h at 37C. Meat serum was prepared from irradiated ground beef, inoculated with either acid‐adapted or nonadapted E. coli O157:H7 and Salmonella, and heated at 58, 62 and 65C to determine D values. D values of acid‐adapted E. coli O157:H7 were higher (P < 0.05) than nonadapted cells at 58, 62 and 65C. Significantly higher (P < 0.05) D values of acid‐adapted Salmonella were observed at 58 and 62C, but not at 65C. D values were 22.46 and 10.59 min at 58C, 3.58 and 1.38 min at 62C, 1.02 and 0.75 min at 65C for acid‐adapted and nonadapted E. coli O157:H7, respectively. D values of acid‐adapted Salmonella were 9.36 min at 58C, 1.66 min at 62C and 1.14 min at 65C, whereas the nonadapted counterparts had D values of 6.44, 0.88 and 0.95 min at 58, 62 and 65C, respectively.PRACTICAL APPLICATIONSFoodborne pathogens exist in the environment in healthy and/or stressed forms and have the potential to contaminate food products. This research was conducted to determine the effectiveness of commonly used heat treatments to eliminate acid‐adapted Escherichia coli O157:H7 and Salmonella in ground beef. There is limited literature on the thermal tolerance of acid adaptation of foodborne pathogens in actual food systems and studies in the past have been conducted at mild heating temperatures, whereas effects of heating to temperatures that are more indicative of cooking temperatures have rarely been researched. This study stresses upon the need for regulatory agencies and large‐scale meat manufacturers to take into consideration the increased thermal tolerance of acid‐adapted pathogens, as healthy growing cultures in a laboratory medium may inaccurately represent their survival in natural food environment.