ARS | Publication request: Analysis of E. coli O157:H7 strains isolated from raw beef contamination events

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 9, 2012
Publication Date: July 20, 2012
Citation: Arthur, T.M. 2012. Analysis of E. coli O157:H7 strains isolated from raw beef contamination events [abstract]. 2012 Beef Industry Safety Summit. Abstract No. 11.

Technical Abstract: Category: Post-harvest pathogen reduction Objective: Contamination of beef trim in commercial establishments can usually be described as occurring at a very low baseline level. However, spurious peaks in contamination rates occur where multiple positive lots are clustered in a short time frame. These peaks have been referred to as contamination “events”. Frequently a cause/source is not identified, and the contamination will be resolved without visible corrective action being taken. There is a large knowledge gap regarding the mechanism of these events. To gain insight into the cause of contamination events, we employed molecular typing of the E. coli O157:H7 isolates collected from events. By typing organisms from multiple lots and time points within an event, and across multiple events, information was available to determine if the contamination derived from a single point source or from multiple sources, as would be expected, if the incoming load were exceeding the capacity of in-plant interventions. It also allowed for tentative determinations regarding where in the process (slaughter floor vs. fab) contamination is occurring and if particular strains are more commonly associated with events. The objectives of this work were to identify if events are: (1) caused by a limited number of strains indicating a single source contamination reservoir, (2) caused by the same strains within a plant over time indicating plant specific reservoir, (3) caused by numerous strains of various types that are not similar over time indicating that antimicrobial interventions are overwhelmed or not working properly for some period of time, or (4) some combination of the above. Also, we sought to determine if particular trim sources are more likely to harbor related strains. Experimental process: Beef trim enrichments representing contamination events were received from multiple commercial beef processing companies. Each enrichment was cultured to recover E. coli O157:H7. Pure strains recovered from culture were analyzed by a novel, non-PulseNetPFGE method. In addition, strain lineages were determined to identify commonalities between strains causing contamination events. Key results: The findings of this study indicate that most contamination events in raw beef products consist of a singular dominant O157 strain type. In these cases the dominant strains were found across multiple product types and separated by substantial spans of time. This would be in disagreement with the current model of beef contamination, which states that the finished product contamination occurs when incoming load (hide and feces carriage of the pathogen) exceeds the capacity of the in-plant interventions to remove carcass contamination. Strain types from incoming load have been analyzed on multiple occasions and have always consisted of a diverse strain set. How this information can be applied to industry: The data obtained in this project lead to the conclusion that contamination events may be the result of contamination occurring after carcasses exit the killfloor. This information should aid the industry in finding solutions to mitigate contamination events. Figure 1. PFGE analysis of E. coli O157:H7 isolates from two contamination events. (Figure 1 also submitted).