Impact of dry chilling on the genetic diversity of Escherichia coli on beef carcasses and on the survival of E. coli and E. coli O157

•Genetic diversity of Escherichia coli on beef remained high during dry chilling.•E. coli from different stages of chilling did not differ in response to desiccation.•Strains of E. coli O157 did not differ from generic E. coli in response to desiccation.•Dry chilling may be used as an effective antimicrobial intervention for beef carcasses.

The objective of this study was to examine the effect of dry chilling on the genetic diversity of naturally occurring Escherichia coli on beef carcasses, and to examine whether two populations of E. coli recovered from carcasses during chilling and E. coli O157 differed in their response to desiccation. Isolates of E. coli were obtained from beef carcasses during a 67 h dry chilling process and were genotyped using multiple-locus variable-number tandem-repeat analysis (MLVA). Ten E. coli genotypes found only at 0 h (group A) and found more than once (group B), as well as five strains of E. coli O157 (group C) were inoculated on stainless steel coupons and their survival was examined after exposure to 75 and 100% relative humidity (RH) at 0 or 35 °C for 67 h. A total of 450 E. coli isolates were obtained, with 254, 49, 49, 51, 23, 20, and 4 from 0, 1, 2, 4, 6, 8 and 24 h of chilling, respectively. No E. coli were recovered at 67 h. MLVA of the isolates revealed 173 distinct genotypes. Genetic diversity of E. coli isolates, defined as ratio of the number of isolates to the number of genotypes, remained between 2.3 and 1.3 during the 24 h of chilling. All strains inoculated on stainless steel coupons and exposed to 75% RH at 35 °C were completely inactivated, irrespective of their groups. Inactivation of E. coli of the three groups was not significantly (P > 0.05) different by exposure to 75% RH at 0 °C. The findings indicate that the genetic diversity of E. coli on beef carcasses was not affected by dry chilling. In addition, inactivation of E. coli genotypes and E. coli O157 by desiccation on stainless steel simulating dry chilling conditions did not differ significantly (P > 0.05). Thus, dry chilling may be used as an effective antimicrobial intervention for beef carcasses.