Biofilm Formation and Sanitizer Resistance Contributes to “High Event” Meat Contamination by Escherichia coli O157:H7

Introduction: Escherichia coli O157:H7 is an important foodborne pathogen. A “High Event” is defined as a time period in which commercial meat plants experience a higher than usual rate of E. coli O157:H7 contamination. Genetic analysis indicated that within a “High Event”, most of the contamination strains belong to a singular dominant O157:H7 strain type. This was in disagreement with the current beef contamination model stating that product contamination occurs when the incoming pathogen load on animal hides, which consists of a diverse strain type, exceeds the intervention capacity. Thus, we hypothesize that the “High Event” contamination is due to certain in-plant colonized E. coli O157:H7 strains that are better able to survive sanitization through biofilm formation.

Purpose: To determine if biofilm formation and sanitizer resistance contributes to “High Event” beef contamination by E. coli O157:H7.  

Methods: A subset of 47 E. coli O157:H7 strains obtained from “High Event” beef contamination and a group of 47 E. coliO157:H7 “Diversity Control Panel” strains were tested for biofilm formation and sanitizer resistance. Biofilm formation was tested on 96-well polystyrene plates for 1 – 6 days. Biofilm cell survival after sanitization was compared between the two strain sets using common sanitizers, including chlorine, Vanquish, and ProOxine.

Results: No difference in “early stage” biofilms was observed between the two strain sets after incubation at room temperature for 1 or 2 days. However, the “High Event” strains demonstrated significantly higher potency (P < 0.05) of “mature” biofilm formation after incubation for 3 – 6 days. The “High Event” strains also exhibited significantly stronger resistance (P < 0.05) to sanitizer treatments.

Significance: These data suggest that biofilm formation and sanitizer resistance play critical roles in “High Event” beef contamination by E. coli O157:H7, which highlights the importance of proper sanitization in commercial meat plants.