Purpose: To examine the effect of dry chilling on the genetic diversity of naturally occurring E. coli population on beef carcasses and on the survival of selected E. coli genotypes.
Methods: Carcasses selected at random were sampled for isolation of E. coli at various intervals for up to 67 h of a commercial chilling process. E. coli isolates were genotyped using multiple-locus variable-number tandem-repeat analysis (MLVA) and genetic diversity was estimated by isolate/genotype ratio. Survival of ten E. coli genotypes found only at 0 h (G1) and appeared at <8 h plus 8 or 24 h (G2) were examined after exposure to 75 and 100% relative humidity (RH) at 0 or 35°C for 67 h.
Results: A total of 254, 49, 49, 51, 23, 20 and 4 E. coli isolates were obtained at 0, 1, 2, 4, 6, 8 and 24 h, respectively. No E. coli was recovered at 67 h. Genetic diversity of isolates obtained between 1 and 24 h ranged from 1.33 to 1.88. All selected genotypes from G1 and G2 were completely inactivated at 75% RH and 35°C. Inactivation of E. coli genotypes from G1 and G2 were not significantly (P>0.05) different by exposure to 75% RH at 0°C and to 100% RH at 0 or 35°C.
Significance: The findings indicate that dry chilling may not impose selective pressure on the survival of E. coli on beef carcasses. Dry chilling could be used as a chemical free option to improve the microbial quality of meat at smaller packing plants.