Effect of pH and temperature on Shiga toxin-producing Escherichia coli O157:H7 isolated from bovine reservoir.

Abstract

The aim of this study was to evaluate the individual and combined effect of pH (between 4.0 and 7.0) and storage temperature (between 6 and 35°C) on two wild-type E. coli O157:H7 (STEC 902 and STEC 2004) strains. The experiments were performed in laboratory culture medium, employing Central Composite Rotational Design (CCRD). For comparison, Enteropathogenic E. coli (EPEC) O55:H7 and non-pathogenic E. coli (npEC) strains were used. To validate the model, seven additional tests not included in the experimental design were performed. The model showed goodness-of-fit. The CCRD results indicated that the temperature significantly affected the microbial population of E. coli strains studied. With best development at temperatures between 20 and 35°C, while refrigeration temperatures (between 6 and 10°C) are unfavorable for the development of STEC O157:H7, independent of pH. The wild-type STEC 902 and STEC 2004 strains showed similar behavior under pH and temperature conditions in laboratory culture medium. On the other hand, control strains showed different behavior than STEC strains, being significantly affected by pH. The data indicate that the response to stress resulting from exposure to different pH and temperature levels varies according to the E. coli strain evaluated.