Substantial within-Animal Diversity of Salmonella Isolates from Lymph Nodes, Feces, and Hides of Cattle at Slaughter

Abstract

ABSTRACTLymph nodes (mandibular, mesenteric, mediastinal, and subiliac;n= 68) and fecal (n= 68) and hide (n= 35) samples were collected from beef carcasses harvested in an abattoir in Mexico. Samples were analyzed forSalmonella, and presumptive colonies were subjected to latex agglutination. Of the isolates recovered, a subset of 91 was characterized by serotyping, pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibility phenotyping.Salmonellawas isolated from 100% (hide), 94.1% (feces), 91.2% (mesenteric), 76.5% (subiliac), 55.9% (mandibular), and 7.4% (mediastinal) of samples. From the 87 typeable isolates, eightSalmonella entericaserotypes, including Kentucky (32.2%), Anatum (29.9%), Reading (17.2%), Meleagridis (12.6%), Cerro (4.6%), Muenster (1.1%), Give (1.1%), and Mbandaka (1.1%), were identified.S. Meleagridis was more likely (P= 0.03) to be recovered from lymph nodes than from feces or hides, whereasS. Kentucky was more likely (P= 0.02) to be recovered from feces and hides than from lymph nodes. The majority (59.3%) of theSalmonellaisolates were pansusceptible; however, multidrug resistance was observed in 13.2% of isolates. Typing by PFGE revealed thatSalmonellastrains generally clustered by serotype, but some serotypes (Anatum, Kentucky, Meleagridis, and Reading) were comprised of multiple PFGE subtypes. Indistinguishable PFGE subtypes and, therefore, serotypes were isolated from multiple sample types, and multiple PFGE subtypes were commonly observed within an animal. Given the overrepresentation of some serotypes within lymph nodes, we hypothesize that certainSalmonellastrains may be better at entering the bovine host than otherSalmonellastrains or that some may be better adapted for survival within lymph nodes. Our data provide insight into the ecology ofSalmonellawithin cohorts of cattle and offer direction for intervention opportunities.