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

Citation

Visvalingam, J., Liu, Y., Yang, X. (2017). 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. International Journal of Food Microbiology, [online] 244 62-66. http://dx.doi.org/10.1016/j.ijfoodmicro.2016.12.022

Plain language summary

Carcass in beef packing plants is generally cooled and/or washed with antibacterial solutions to suppress the growth of Escherichia coli and related foodborne pathogens like E. coli O157. This may select for bacteria that are resistant to a specific stress, which is represented as a decrease in bacterial genetic diversity. Dry chilling is one of the ways in which a carcass is chilled by a flow of refrigerated air. This study aimed to examine the effect of dry chilling on the genetic diversity of naturally occurring E. coli on beef carcasses, and to examine whether E. coli recovered from carcasses during chilling and E. coli O157 differ in their response to desiccation. We obtained E. coli isolates on beef carcasses at different time intervals during the dry chilling process and evaluated the bacterial type diversity. The survival of generic E. coli and E. coli O157 was determined in lab desiccation conditions simulating commercial chilling process. The diversity of E. coli on beef remained high and did not change significantly during dry chilling. No E. coli were recovered at the last time point of dry chilling, 67 h. The survival rate of generic E. coli and E. coli O157 to desiccation did not differ. The findings indicate genetic diversity of E. coli on beef carcasses was not affected by dry chilling and therefore, does not put selective pressure for selecting E. coli that are more resistant to desiccation. Dry chilling may be used as an effective method for preventing growth of E.coli.

Abstract

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.

Publication date

2017-03-06

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