PATHOGEN MITIGATION IN LIVESTOCK AND RED MEAT PRODUCTION
Location: Meat Safety & Quality Research
Title: Microbiological analysis of bovine lymph nodes for the detection of Salmonella enterica
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 14, 2012
Publication Date: May 5, 2012
Citation: Harhay, D.M., Arthur, T.M., Bosilevac, J.M., Kalchayanand, N., Schmidt, J.W., Wang, R., Shackelford, S.D., Loneragan, G.H., Wheeler, T.L. 2012. Microbiological analysis of bovine lymph nodes for the detection of Salmonella enterica. Journal of Food Protection. 75(5):854-858.
Interpretive Summary: Bovine lymph nodes have been identified as a potential source of Salmonella when carcass fat trim containing these nodes is incorporated into ground beef. Experiments conducted to better understand and quantify this risk need to ensure that when Salmonella is detected from a lymph node sample, that it originated from within the lymph node, and was not a cross-contaminant from the surrounding fat. The objectives of this study were to determine the potential for cross-contamination from fat, to confound the microbiological analysis of lymph nodes and to evaluate submersion in boiling water as a strategy to ensure accurate lymph node analysis. Results showed that cross-contamination from surface fat to residing lymph nodes did occur during sample preparation. However, submersion in boiling water was successful as a means of surface decontamination and did not adversely affect Salmonella contained within the lymph node. Thus, use of the methods described will increase the accuracy of Salmonella detection in bovine lymph nodes, and will aid in the assessment of the potential risk these tissues pose, when incorporated in ground beef.
Bovine peripheral lymph nodes (LNs) have been identified as a potential source of Salmonella when trim containing these nodes is incorporated into ground beef. Studies examining the prevalence of Salmonella in peripheral LNs of cattle are few in number and the microbiological methods used for these analyses have not been validated. Given that Salmonella contamination may be found on post-intervention carcasses, it is important to understand the extent to which Salmonella contamination from surrounding adipose tissue is transferred to LN samples during sample preparation. To better understand the potential for cross-contamination, we analyzed 906 LN samples and their corresponding adipose trim (AT) for the presence of Salmonella. Results showed that Salmonella prevalence in LNs and on AT was low (0.8 and 5%, respectively), but that it was possible to find AT positive for Salmonella contamination while the corresponding LNs were negative, and vice versa. In order to examine the dynamics of cross-contamination between surface adipose and LNs in the trimming process, inoculation studies were performed. The efficacy of LN submersion in boiling water as a means of surface sterilization and the effect of boiling on the viability of Salmonella contained within LN samples was also examined. Results show that on average 23 to 43% of LN samples may be cross-contaminated by Salmonella on surrounding adipose when present in the range of 10*1 to 10*2 CFU per sample, however, surface decontamination methods were very effective at removing Salmonella cross-contaminants in this range.