Microbiological analysis of bovine lymph nodes for the detection of Salmonella enterica

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 postintervention 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 crosscontamination, 906 LN samples were collected from postintervention carcasses and these, along with the corresponding adipose trim (AT), were analyzed for the presence of Salmonella. The results showed that the Salmonella prevalence in LNs and on AT was 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 tissue 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 were also examined. The results showed that, on average, 23 to 43% of the inoculated LN samples in this study were cross-contaminated by Salmonella on surrounding adipose tissue when present in the range of 10¹ to 10² CFU per sample; however, surface decontamination methods were very effective at removing Salmonella cross-contaminants in this range.