SF6029 - Establishment of Critical Control Points for Enteric Pathogens in Beef Production

Researcher:

Dr. Keith Warriner, Dept. of Food Science, University of Guelph

Objectives:

1. By using a combination of molecular typing and indicator counts establish critical control points for enteric pathogen contamination from farm to post-chilling and grinding.
   

2. To correlate the mud score of steers and the significance of aeromicrobiology in determining the microbiological quality of carcasses at post-chilling.
   

3. Provide recommendations on the adequacy of current sampling schemes performed within Ontario.

Expected Benefits:

1. The results of the work will establish the critical control points in two diverse plants and provide background data on the need to apply mandatory HACCP. In addition, by understanding the dynamics of enteric contamination within slaughter lines more representative standardized sampling regimes can be formulated.

Summary of Research Results:

Although relatively rare, Escherichia coli O157:H7 represents a significant food safety issue to the beef industry. The pathogen is highly virulent and can cause serious illness or death even when ingested in low numbers (10-100 cells). Cattle can carry E. coli O157:H7 within their gastro-intestinal tract without showing any outward signs of illness. At the farm level only a relatively small proportion of cattle are thought to carry E. coli O157:H7, however, the prevalence of the pathogen associated with animals/carcasses can increase significantly during processing. Here fecal material from an infected animal can be transferred directly to non-infected cattle and subsequently become distributed within the slaughter line where further cross-contamination events can take place.

To reduce the carriage of pathogens on beef, large meat packing facilities employ Hazard Analysis of Critical Control Point (HACCP) systems. Here, interventions such as steam pasteurization and/or organic carcass washes aim to remove any contamination acquired during the slaughter process. However, it is becoming established that current interventions are not totally reliable even when used in combination. Therefore, a more effective strategy is to prevent the spread of pathogens, such as E. coli O157:H7, between animals/carcasses prior to and during processing. However, a detailed knowledge on the dissemination routes of enteric contamination is required in order to identify which points in the chain control should be exercised. To this end, the aim of the current study was to identify the routes by which enteric contamination is transferred between animals/carcasses within small and large capacity beef slaughter lines. DNA fingerprinting was used to track and trace contamination associated with individual animals. DNA typing is a very sensitive technique and can be used to differentiate closely related bacterial strains. This enables contamination from individual animals to be identified and hence traced. Because E. coli O157:H7 only occurs sporadically on cattle tracing the pathogen directly would not yield a complete picture on the routes of dissemination. Therefore, non-pathogenic (generic) E. coli was selected as a marker bacterium since it is recovered in higher numbers from fecal material compared to its pathogenic relative.

In each of the slaughter house visits, surface samples from carcasses and the environment were collected at different points within the processing chain over a typical day's production period. Generic E. coli was isolated from the various samples and DNA fingerprints prepared using ERIC-PCR. By comparing the DNA fingerprints of the E. coli isolates it was shown that cross-contamination events can occur at the farm level, during transportation, pre-slaughter holding and during processing. In the small slaughter line the majority of cross-contamination events occurred at the farm level. Cross-contamination also occurred during transportation and via contact with common surfaces such as floors and the cradle used during carcass dressing. Airborne contamination did not significantly contribute to the spread of contamination between carcasses. It was found the levels of contamination on carcasses entering the cooler were dependent on the initial levels on cattle entering the line.

In the large capacity line there was significant cross-contamination between carcasses during the holding period prior to slaughter. Contamination on the hides of cattle was then directly or indirectly (via the air) transferred to the carcass surface during hide removal. Contamination released from hides also spread throughout the line and hence contaminated further carcasses. Interestingly, evisceration did not contribute significantly to the final bacterial loading on carcasses in either of the slaughter houses visited.

The study illustrated that the microbiological quality of carcasses processed within small and large capacity slaughter lines are comparable. However, as may have been expected, the transfer of contamination between animals/carcasses occurred more frequently in the large capacity slaughter line. In terms of enhancing food safety of beef, it can be envisaged that small capacity lines would benefit from the introduction of on-farm interventions that prevent the spread of pathogens between cattle. Increased sanitation of the interior of trailers used to transport cattle and switching from bed to rail-hide removal would also be of benefit. In large capacity lines increased sanitation in holding areas and modifying the air flow to minimize airborne contamination would reduce the transfer of enteric bacteria between carcasses.

A further highlight of the study was the finding that E. coli populations within beef chains are highly complex. It was noted that a proportion of genotypes persisted over extended time periods (i.e. endemic) whilst others had a transient existence. In practical terms this finding has a significant impact on the use of E. coli count data in assessing the microbiological status of carcasses and slaughter house environments (i.e. the strain present is more critical than actual levels). In this respect DNA fingerprinting provides a powerful tool for developing and verifying HACCP plans within meat processing chains.