Purpose: The purpose of this study was to 1) determine the prevalence of Salmonella isolated from LNs and feces of cattle at harvest in a Mexican slaughter facility and to 2) characterize the isolates to identify how Salmonella might be entering the animal and colonizes LNs throughout the body.
Methods: From each carcass (n=68), LNs (subiliac, mandibular, mediastinal and mesenteric) and feces were collected during harvest in a Mexican slaughter facility. All samples were enriched in tryptic soy broth (TSB), subjected to immunomagnetic separation (IMS), streaked on xylose lysine desoxycholate (XLD) agar and confirmed as Salmonella via latex agglutination. Pulsed field gel electrophoresis (PFGE) typing was performed to characterize Salmonella isolates from select carcasses that harbored Salmonella in multiple LNs and resultant patterns were analyzed to probe similarities among samples from the same animal, as well as the same tissues from different animals.
Results: The prevalence of Salmonella was 55.9% (95% CI: 43.8-68.0%), 91.2% (95% CI: 84.3-98.1%), 7.4% (95% CI: 1.0-13.7%), 76.5% (95% CI: 66.1-86.8%), 94.1% (95% CI: 88.4%-99.9%) for mandibular LN, mesenteric LN, mediastinal LN, subiliac LN and feces, respectively. PFGE patterns were identical for the subiliac and mesenteric LNs within the same animal, the mesenteric LN and feces within the same animal, and the mediastinal LNs among different animals.
Significance: Results suggest that Salmonella is commonly harbored in cattle LNs and PFGE patterns indicate that certain Salmonella strains may be more likely to colonize different LNs, suggesting various methods of entry. These findings should be further investigated to gain a better understanding of routes of infection and opportunities for Salmonella control in ground beef products.