Prevalence and Characterization of Salmonella in Bovine Lymph Nodes Potentially Destined for Use in Ground Beef†

Abstract

A potential source of pathogenic bacteria in ground beef is the lymphatic system, specifically the lymph nodes. Bacteria have been isolated from the lymph nodes of cattle at slaughter; however, most studies have dealt with mesenteric lymph nodes, which are not normally incorporated into ground beef. The objective of the current study was to determine the prevalence and multidrug-resistance status of Salmonella in bovine lymph nodes associated with lean and fat trimmings that might be utilized in ground beef production. Bovine lymph nodes (n = 1,140) were collected from commercial beef processing plants. Half of the lymph nodes sampled were obtained from cull cow and bull processing plants, and the remainder were obtained from fed beef processing plants. Lymph nodes located in chuck and flank adipose tissue were collected for this study. Salmonella prevalence in the lymph node samples was low, with an overall prevalence of 1.6% and a 95% confidence interval of 0.85 to 2.3%. Lymph nodes from cull cattle carcasses had a higher prevalence of Salmonella than did those from fed cattle carcasses. Lymph nodes from the flanks of cow and bull carcasses had the highest prevalence at 3.86%, whereas lymph nodes from the chuck region of fed cattle carcasses had the lowest prevalence at 0.35%. Three of the 18 Salmonella-positive lymph node samples contained multidrug-resistant Salmonella, and all 3 samples were from cull cattle.

Diversity of Multidrug-Resistant Salmonella enterica Strains Associated with Cattle at Harvest in the United States

“…The Salmonella strains found contaminating these carcasses were those of MDR Salmonella Typhimurium in one event and pansusceptible Salmonella Dublin in the other, both serotypes known for causing clinical illness in cattle. This observation prompted a comparison of the Salmonella serotypes reported in a number of studies, including serotypes found in ground beef (14,75,79), those isolated from cattle lymph nodes (8), and those found on final carcasses in this study, along with serotypes noted for being isolated from clinically infected cattle (21,22). The last group was identified from the Salmonella Surveillance Annual Summary reports for 2005 and 2006, which summarize the Salmonella strains isolated and serotyped from clinical cases of animal disease that were reported to the Centers for Disease Control and Prevention (CDC) and the National Veterinary Services Laboratory (NVSL) in those time periods.…”

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

“…A recent but growing body of evidence demonstrates that cattle lymph nodes commonly harbor Salmonella (20)(21)(22)(23) and that, when incorporated into ground beef, lymph nodes may contribute to the observed discrepancy between effective control on carcass surfaces and subsequent isolation from ground beef. A more complete understanding of the ecology of cattle and Salmonella is needed.…”

Isolation of Escherichia coli from lymph nodes of bovine carcasses and detection of hlyA gene with PCR

“…La contaminazione delle carni da parte di batteri è responsabile di diverse migliaia di malattie alimentari ogni anno negli Stati Uniti (T. M. Arthur, et al, 2008). Il principale mezzo per ridurre e prevenire questo tipo di malattia consiste nell'identificare le fonti di contaminazione e minimizzarle o rimuoverle dal processo produttivo.…”

“…Tuttavia, anche dopo la realizzazione di questi interventi, batteri patogeni possono ancora essere isolati da alimenti quali la carne macinata: questo molto probabilmente evidenzia esistono altre fonti di contaminazione. Una possibile fonte di batteri patogeni per la carne bovina è il sistema linfatico ed in particolare i linfonodi (T. M. Arthur, et al, 2008;BarkocyGallagher, et al, 2003;Bonardi, Foni, Chiapponi, Salsi, & Brindani, 2007;Bosilevac, et al, 2004;Sofos, et al, 1999). Il sistema linfatico è coinvolto nelle funzioni immunitarie agendo con un meccanismo di filtrazione in grado di sequestrare batteri, virus e altri agenti estranei all'organismo al fine di permettere l'eventuale distruzione da parte dei linfociti.…”

“…notarono che nonostante Salmonella venisse isolata frequentemente dai linfonodi cecali e digiunali, quest'ultima non veniva mai rinvenuta dai linfonodi duodenali dei medesimi animali (Samuel, et al, 1979). Queste e altre considerazioni simili spingono i ricercatori a concludere che una significativa diffusione di Salmonella attraverso i linfonodi meseraici non si realizzi (T. M. Arthur, et al, 2008;Cenci-Goga, et al, 2007;Anonymous, 2009). Molte delle ricerche effettuate finora si sono occupate dei linfonodi meseraici, i quali non si ritrovano nella carne macinata.…”