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Salmonella Harboured in Lymph Nodes of Cattle

05 June 2012

Salmonella in beef cattle can evade detection because it becomes hidden in the lymph nodes of the carcase and in consequence can increase the contamination of ground beef products, writes Chris Harris.

Speaking at the recent American Meat Institute Expo and Conference, Sara E Gragg from Texas Tech University said that to reduce the incidence of Salmonella contamination of meat products it is necessary to have pre-harvest, post-harvest and final product treatment.

A research study by the US meat Animal Research Centre and Texas Tech University found that Salmonella carcase contamination for fed cattle ranged between the per cent and 24.9 per cent.

However, following the removal of the hide and other interventions this contamination dropped to less than one per cent.

In ground beef products further down the processing chain the contamination had leapt to 4.2 per cent.

This led the researchers to look at the contamination in the subiliac lymph nodes of both feedlot and cull dairy cattle.

The study looked to see what the salmonella serotypes were and whether they were susceptible to drug treatments.

The tests were taken from cattle from three regions of the US over three seasons - autumn, winter and spring and summer. The results showed that there was a variation in different samples according to the animal types and the seasonality.

The most frequent types of Salmonella that were found were Montevideo and Anatum, with Montevideo being the most common type in ground beef.

However, the study also found that 7.1 per cent of the samples taken were multidrug resistant to five drugs or more.

Overall the greatest number of cases of Salmonella that were found were in feedlot cattle with 15.5 per cent of the samples proving positive. By contrast the cull dairy cattle only showed 1.8 per cent of the samples as positive.

The peak prevalence of Salmonella in the cattle was in the period of summer into autumn and most of the positive samples came from those taken in the Southern High Plains compared to the Midwest or West Coast.

Ms Gragg said that the Salmonella contamination could find its way to the lymph nodes either through the skin, through infected abrasions, or through gastrointestinal means.

She said that a second study also looked at the prevalence of salmonella in cattle faeces and in the lymph nodes of cattle at the time of slaughter from farms in Mexico. In this study the research team examined other lymph nodes as well as the subiliac, including the mandibular, mesenteric and mediastinal.

The findings showed that multiple lymph nodes throughout the cattle carcase are capable of harbouring Salmonella, although certain forms of Salmonella are more likely to be found in specific lymph nodes.

Ms Gragg said that it is possible to investigate using microbial feeds to prevent Salmonella contamination build up in the lymph nodes, but interventions before and after slaughter as well as treatments of the final product are the most thorough ways of preventing Salmonella contamination in cattle becoming a serious risk to public health.

June 2012

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