Towards an understanding of how Salmonella potentially evades beef carcass processing interventions

Authors: Harhay, Dayna; GRAGG, SARA - Texas Tech University; Smith, Timothy - Tim; Arthur, Terrance; Bosilevac, Joseph - Mick; Kalchayanand, Norasak - Nor; Schmidt, John; Wang, Rong; Shackelford, Steven; Wheeler, Tommy; BRASHEARS, MINDY - Texas Tech University; BROOKS, J - Texas Tech University; BROWN, TYSON - Texas Tech University; Harhay, Gregory; LONERAGAN, GUY - Texas Tech University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/11/2011
Publication Date: 3/2/2011
Citation: Brichta-Harhay, D.M., Gragg, S.E., Smith, T.P.L., Arthur, T.M., Bosilevac, J.M., Kalchayanand, N., Schmidt, J.W., Wang, R., Shackelford, S.D., Wheeler, T.L., Brashears, M.M., Brooks, J.C., Brown, T.R., Harhay, G.P., Loneragan, G.H. 2011. Towards an understanding of how Salmonella potentially evades beef carcass processing interventions [abstract]. 2011 Beef Industry Safety Summit. Abstract No. 2.

Interpretive Summary:

Technical Abstract: Background: The beef production industry has grappled with the issue of Salmonella contamination in final products for the better part of two decades. Despite significant strides in reducing Salmonella prevalence and load on beef carcasses at harvest, low-level contamination of final product persists. Two possible mechanisms by which Salmonella may evade carcass interventions are: 1) internalization within host lymphatic tissues that may be incorporated into ground beef via fat trim and 2) adaptation to the environmental stress imposed by carcass interventions. In order to better understand the extent to which Salmonella are exploiting these mechanisms, we undertook the following experiments: Objectives: 1) Determine the prevalence of Salmonella in subiliac lymph nodes obtained from cattle at harvest. 2) Characterize the gene expression response of a multidrug resistant (MDR) Salmonella Newport strain when exposed to simulated beef carcass processing interventions. Methods/Results 1: Lymph nodes were collected from the carcasses of feedlot cattle and dairy cows in commercial packing plants. Lymph nodes were trimmed and surface sterilized prior to enrichment for Salmonella. Enrichments were subjected to immunomagnetic separation in order to capture and concentrate any Salmonella present. Presumptive Salmonella isolates were confirmed by invA PCR and serotyped. Between September and November of 2010, the mean prevalence of Salmonella in cattle lymph nodes (n=1,039) was 8.7% (95% CI 0.93 – 16.6%). The majority of these Salmonella were identified as serotypes Montevideo and Anatum. Implications 1: Given that Salmonella was readily recovered from subiliac lymph nodes, fat trim containing lymph nodes may be a point source for Salmonella entry into ground beef products. The public health consequence of these findings should be further investigated with research aimed at revealing the routes of infection and developing strategies to eliminate the presence of Salmonella in the lymph nodes of healthy cattle. Methods/Results 2: MDR S. Newport was challenged by sequential exposure to thermal stress (80°C), 2% lactic acid (55°C) and cold stress (4°C). Gene expression, of challenged and control cultures, was characterized and compared. This study showed that intervention exposure resulted in the increased expression of 761 genes (approximately 16% of 4,613 genes examined). Genes demonstrating the greatest fold change included those with roles in the heat shock response, DNA repair and a number of regulatory systems that govern the Salmonella virulence response. Implications 2: The expression profiles described present a picture of the molecular strategies Salmonella employs to survive multiple hurdle beef carcass processing interventions. These data reveal chinks in the armor of Salmonella that potentially may be exploited to combat their entry into the beef food chain.