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Foodborne Pathogens on Cattle Hides

04 June 2010

Modern microbial beef safety concept is based on a farm-to-fork principle that involves a wide range of coordinated control measures applied at all relevant steps in the beef chain, writes S Buncic from University of Novi Sad, Faculty of Agriculture, Department of Veterinary Medicine in Serbia in a paper for the Advancing Beef Safety through Research and Innovation conference.

At abattoirs, certain microbial contamination of bovine carcasses during slaughter and dressing operations is inevitable and occurs at abattoirs in spite of adherence to process hygiene principles. Consequently, cattle carcass decontamination interventions have been considered, and widely used in beef abattoirs in some countries (e.g. USA), as a means to eliminate foodborne pathogens from carcasses. This approach could be seen as “reactive”, as it deals with the problems after they occurred. In any case, the ultimate effectiveness of antimicrobial treatments, when assessed through the levels of surviving microflora remaining on treated substrate, depends on the initial microbial load to a great extent. Better ultimate results of the antimicrobial treatment are achieved when applied to cleaner substrate. Therefore, preventative approach, using hygiene-based measures, is universally and mandatorily used in the beef chain including at abattoirs, but can be complemented with the “reactive” approach in some situations within the regulatory frame.

Bovine carcasses may become contaminated with enteric pathogens during slaughter and dressing operations primarily from faecal material originating from the gut content or the hide. Today, in modern abattoirs, spillage of the gut content onto the carcass during evisceration operation occurs only rarely. However, based on numerous published studies, it has been widely recognised that the hide is the main source of direct and/or indirect microbial contamination of bovine carcasses. This has been supported by research findings that the occurrence of microbial pathogens (e.g. E. coli O157) on cattle hides and dressed bovine carcasses can be significantly correlated both quantitatively and with respect to relatedness of particular molecular subtypes of bacteria. Although a relatively small proportion (<0.1%) of hide microflora is transferred onto meat during direct contact, because very high microbial levels on hide exist (6-10 log/cm2), the counts of bacteria remaining on meat post-contact are still very significant. Therefore, hide-meat contact must be either totally prevented during, or pathogens must be eliminated from hide before, skinning of carcasses.

Data from published studies indicate that levels of general microflora on hides are relatively high and highly variable. Approximately, total count of bacteria can vary between 4 and >10 log per cm2 of hide, Enterobacteriaceae between 2 and 5 log, and generic Escherichia coli between 1.5 and 5.5 log. Furthermore, reported incidences of main bacterial foodborne pathogens on cattle hides are also relatively high and variable e.g. E. coli O157 between 7.5% and 100%, Salmonella between 3.3% and 100%, Campylobacter between 2.1% and 13%, and Listeria monocytogenes between 0.8% and 47.9%. A number of pre-slaughter factors differing between studies contribute to such a high variability of reported hide microflora including on-farm bacterial incidences/prevalences, animal production systems and animal husbandry, seasons, visual animal cleanliness, sample sizes, and sampling and microbiological methods. Furthermore, animal transport and lairaging (TL phase) lead to increased faecal shedding and/or levels of foodborne pathogens in animals including on hides, and microbial cross-contamination occurs via animal-to-animal and/or animal-to surfaces-to animal routes. The main factors contributing to the increasing occurrence of pathogens in animals during TL phase include mixing of animals of different origin, stress, extended TL duration, visual dirtiness of animals, and dirtiness of transport vehicles and lairage pens. Understandably, pre-slaughter controls of pathogens on hides including during TL phase are focused on effective measures to prevent/minimize these contributing factors. In particular, effective sanitation of vehicles and pens is essential to reduce T-L-related cross-contamination of hides, but naturally-occurring pathogens (e.g. Salmonella, E. coli O157) often persist on surfaces even after routine sanitation. Overall, these measures applied alone seem insufficiently effective; and even visually clean hides harbour high levels of microorganisms that often include pathogens.

More recently, additional hide-related controls have been considered including various treatments of hides (i.e. decontamination) applied after slaughter but before skinning of cattle to eliminate (kill) pathogens. The reported reductions in microbial and foodborne pathogens’ counts on hides achievable by various treatments (e.g. singeing, commercial sanitizers or disinfectants, organic acids, sodium hydroxide, electrolysed water) under experimental conditions range from 1 log to 4-5 log, but under commercial abattoir conditions they are most commonly around 2-3 log reduction levels.

Most recently, our research has been focused on a novel approach to pre-skinning hide treatment so that it includes microbial fixation (immobilisation) on the hair. With this approach, the hide microflora including foodborne pathogens does not need necessarily to be entirely killed. Rather, the hide can be treated with some compounds that would just prevent microflora detaching from the hair, and thus prevent contamination of the carcass meat during skinning. A range of potential microflora-hide fixation/immobilisation compounds were considered. The results gathered to-date indicate that some natural resins commercially available as a glazing agent in food (e.g. candy or fruit) industry appear very promising. For example, treatment of hide with a solution of 30% Shellac (an insect-produced natural resin-based glazing agent) in ethanol resulted in up to several log reduction of natural total viable count and in >3-fold prevalence reduction of naturally-occurring E. coli O157.

In conclusion, as a meat safety measure, post-slaughter but pre-skinning hide treatment can be considered as a “proactive” approach to beef safety as it deals with the cause of microbial contamination of bovine carcasses i.e. with potential beef safety problems before they occur. It can be routinely used either alone or in combination with the end-product (dressed carcass) decontamination. It can be expected that, in the latter case, overall improvement of the microbiological status of the meat would be determined by a combination of microbial reductions achieved by both treatments, and very likely exceeding the improvements presently achievable by skinned carcass decontamination alone.

Further Reading

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June 2010

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