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

Authors: GRAGG, SARAH - Texas Tech University; LONERAGAN, GUY - Texas Tech University; NIGHTINGALE, KENDRA - Texas Tech University; Harhay, Dayna; RUIZ, HENRY - Texas Tech University; ELDER, JACOB - Texas Tech University; GARCIA, LYDA - Texas Tech University; MILLER, MARKUS - Texas Tech University; ECHEVERRY, ALEJANDRO - Texas Tech University; PORRAS, ROSA - Autonomous University Of Yucatan; BRASHEARS, MINDY - Texas Tech University

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2013
Publication Date: 8/1/2013
Publication URL: http://handle.nal.usda.gov/10113/60854
Citation: Gragg, S.E., Loneragan, G.H., Nightingale, K.K., Harhay, D.M., Ruiz, H., Elder, J.R., Garcia, L.G., Miller, M.F., Echeverry, A., Porras, R., Brashears, M. 2013. Substantial within-Animal Diversity of Salmonella Isolates from Lymph Nodes, Feces, and Hides of Cattle at Slaughter. Applied and Environmental Microbiology. 79(15):4744-4750.

Interpretive Summary: Beef carcass lymph nodes have been identified as a potential source of human exposure to Salmonella, when fat trim containing these nodes is mixed with lean trim and incorporated into ground beef. In order to gain a better understanding of the diversity of Salmonella within and among lymph nodes of cattle, and to determine if certain Salmonella serotypes are over-represented within lymph nodes in comparison with other sites associated with cattle, lymph nodes, fecal, and hide samples were collected from cattle at harvest in a beef processing plant in Mexico. Serotype and DNA fingerprinting pattern diversity were determined for Salmonella isolated from carcasses with five or more sample types positive for Salmonella contamination. The data collected show that multiple Salmonella serotypes and DNA fingerprint subtypes may be readily recovered from lymph nodes, hide and fecal samples of a given carcass. These data support the hypothesis that Salmonella present in cattle lymph nodes may likely gain entry through cuts in the skin, and thus the diversity of Salmonella observed in lymph nodes of a given carcass, to an extent reflects the diversity of Salmonella in cattle environments. Further, these data provide insight into the ecology of Salmonella within cohorts of cattle and offers direction for intervention opportunities.

Technical Abstract: Lymph 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 for Salmonella and presumptive colonies 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. Salmonella was 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 typable isolates, eight Salmonella serotypes were identified including Kentucky (32.2%), Anatum (29.9%), Reading (17.2%), Meleagridis (12.6%), Cerro (4.6%), Muenster (1.1%), Give (1.1%), Mbandaka (1.1%). S. Meleagridis was more likely (P=0.03) recovered from lymph nodes than feces or hides whereas S. Kentucky was more likely (P=0.02) recovered from feces and hides than lymph nodes. The majority (59.3%) of Salmonella was pansusceptible; however, multidrug resistance was observed in 13.2% of isolates. Typing by PFGE revealed that Salmonella 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 certain Salmonella may be better at entering the bovine host than other Salmonella or some may be more adapted for survival within lymph nodes. Our data provide insights into the ecology of Salmonella within cohorts of cattle and offers direction for intervention opportunities.