Assessment of Salmonella Prevalence in Lymph Nodes of U.S. and Mexican Cattle Presented for Slaughter in Texas

Foodborne salmonellosis has been traced to undercooked ground beef and other beef products in the past, and peripheral lymph node (LN) presence in the fatty tissues of beef carcasses is one possible source of Salmonella contamination. Researchers have previously reported higher rates of Salmonella prevalence in LNs from cattle raised and harvested in Mexico compared with rates typically observed from cattle harvested in the United States. With cattle of Mexican origin comprising the majority of U.S. live cattle imports, the objectives of this study were designed to determine whether Salmonella prevalence in LNs differed (i) between cattle of Mexican and U.S. origins when exposed to the same South Texas feeding operation and (ii) between warm and cool seasons. To meet these objectives, paired (left and right sides) subiliac LNs ( n = 800 LNs; n = 400 pooled samples) were collected from 100 carcasses per origin (Mexico and United States) per season (cool, December to January; warm, July to September). Overall, Salmonella prevalence in LN samples was 52.0% (208 of 400). No difference ( P = 0.4836) was seen in Salmonella prevalence as a function of origin, with 54.0% (108 of 200) and 50.0% (100 of 200) of LN samples returning Salmonella-positive results from cattle of Mexican and U.S. origin, respectively. Salmonella prevalence differed ( P = 0.0354) between seasons, with 46.5% (93 of 200) of cool and 57.5% (115 of 200) of warm season samples returning Salmonella-positive results. Serotyping of PCR-confirmed positive samples resulted in 14 different serovars being identified, with Cerro (21.6%), Anatum (19.7%), Muenchen (17.8%), Montevideo (14.4%), and Kentucky (12.0%) comprising the majority of serovars. These results suggest that factors other than cattle origin may be impacting Salmonella prevalence rates in bovine LNs and that additional research is needed to better understand the role of environment and management-related factors on Salmonella prevalence in bovine LNs.