Characterization of Escherichia coli O157:H7 Strains from Contaminated Raw Beef Trim during “High Event Periods”

Abstract

The development and implementation of effective antimicrobial interventions by the beef processing industry in the United States have dramatically reduced the incidence of beef trim contamination by Escherichia coli O157:H7. However, individual processing plants still experience sporadic peaks in contamination rates where multiple E. coli O157:H7-positive lots are clustered in a short time frame. These peaks have been referred to as "high event periods" (HEP) of contamination. The results reported here detail the characterization of E. coli O157:H7 isolates from 21 HEP across multiple companies and processing plants to gain insight regarding the mechanisms causing these incidents. Strain genotypes were determined by pulsed-field gel electrophoresis, and isolates were investigated for characteristics linking them to human illness. Through these analyses, it was determined that individual HEP show little to no diversity in strain genotypes. Hence, each HEP has one strain type that makes up most, if not all, of the contamination. This is shown to differ from the genotypic diversity of E. coli O157:H7 found on the hides of cattle entering processing plants. In addition, it was found that a large proportion (81%) of HEP are caused by strain types associated with human illness. These results pose a potential challenge to the current model for finished product contamination during beef processing.T he development and implementation of effective antimicrobial interventions by the beef processing industry in the United States have reduced the incidence of beef trim contamination by Escherichia coli O157:H7. These improvements have resulted in decreased contamination rates of raw beef trim by the bacterial pathogen E. coli O157:H7, to an estimated national prevalence of 0.39% (1). However, individual processing plants experience sporadic peaks in contamination rates where multiple positive lots are clustered in a short time frame. These peaks have been referred to as "high event periods" (HEP) of contamination. The Food Safety and Inspection Service (FSIS) of the USDA has defined HEP as production intervals during which slaughter establishments experience high rates of positive results for E. coli O157:H7 (or Shiga-toxigenic E. coli [STEC] or virulence markers) in trim samples (2). Typically, a cause/source for a HEP is not identified, and the contamination event will be resolved before notable correction of the process can be performed.The current model of finished product contamination during beef processing starts with the pathogen load on the hides of cattle entering the processing plant. Several studies (3-5) have identified the hide as the major source of E. coli O157:H7 contamination of carcasses during processing. Once contamination has been transferred from the hide to the carcass during dehiding, it must be removed or destroyed through antimicrobial interventions to prevent finished product contamination. However, research has indicated that interventions or even systems of multiple interventions can be overwhe...

Biofilm Formation and Sanitizer Resistance of Escherichia coli O157:H7 Strains Isolated from “High Event Period” Meat Contamination

“…The testing strains of the two collections included 45 strains of E. coli O157:H7 isolated from HEPs and 47 E. coli O157:H7 strains of the U.S. Meat Animal Research Center O157 diversity control panel that were isolated from animal hide swabs of beef cattle during harvest at the processing plants. The HEP isolates were strains representing the genotypes associated with 14 HEPs and were recovered from enrichments as described previously (1). The U.S. Meat Animal Research Center diversity panel represents the breadth of E. coli O157:H7 pulse-field gel electrophoresis types from over 1,000 cattle hide samples collected previously (4).…”

Evaluation of sodium dichloroisocyanurate treatment on recovered concentrations of Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes from cattle hide surfaces and culture medium

“…Also Pohlman et al reported that 10% TSP reduced microbial populations in beef samples and improved color of meat product (Pohlman, Stivarius, McElyea, & Waldroup, 2002). However, the efficacy of such methods and antimicrobials may be limited in its effectiveness to reduce microorganism when high levels of pathogenic bacteria are harbored in fecal and mud become firmly incorporated onto cattle hides (Arthur et al, 2014).…”

“…Cattle surfaces contaminated from fecal material and mud are the main hurdles for insuring safe meat because such debris may lead to carcass contamination during cattle processing as a result of direct contact of meat with the contaminated hide surfaces and spent waste water (Arthur, Bono, & Kalchayanand, 2014; Elder et al, 2000). Incorporation of antimicrobial application and stringent sanitary practices have limited cross contamination and enhanced quality of beef products at processing facilities (Arthur et al, 2014; Dickson & Acuff, 2017; Dickson & MacNeil, 1991; Long III, Sarker, & Liu, 2018; Mies et al, 2004). In previous studies, cetylpyridinium chloride spraying on beef carcass resulted in Escherichia coli O157:H7 and Salmonella Typhimurium reduction up to 5–6 log CFU cm −2 (Cutter et al, 2000).…”

Escherichia coli O157:H7 Strains Isolated from High-Event Period Beef Contamination Have Strong Biofilm-Forming Ability and Low Sanitizer Susceptibility, Which Are Associated with High pO157 Plasmid Copy Number

“…The precise cause or contamination source responsible for HEPs is not well understood. Our previous study (1) indicated that, within each HEP event, most of the E. coli O157:H7 strains belonged to a singular dominant strain type. This observation was in disagreement with the traditional beef contamination model, which states that contamination occurs when the incoming pathogen load on animal hides, which consists of widely diverse strain types of E. coli O157:H7, exceeds the intervention capacity of the plants.…”