|Koohmaraie, Mohhammad -|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 2, 2011
Publication Date: March 1, 2011
Citation: Harhay, D.M., Arthur, T.M., Bosilevac, J.M., Kalchayanand, N., Shackelford, S.D., Wheeler, T.L., Koohmaraie, M. 2011. Diversity of multidrug-resistant Salmonella enterica strains associated with cattle at harvest in the United States. Applied and Environmental Microbiology. 77(5):1783-1796. Interpretive Summary: Salmonella is an important foodborne pathogen, causing millions of cases of food poisoning in the U.S. each year. While poultry products and contaminated fresh produce are well-established vectors for Salmonella, several foodborne disease case studies have shown that undercooked ground beef has also been a source of sporadic and outbreak cases of salmonellosis. Moreover, antibiotic use in production agriculture has raised concerns that food animals are increasingly becoming reservoirs for drug-resistant pathogens. To gain a better understanding of the risk of introducing drug-resistant Salmonella into the beef food chain, we examined the prevalence and diversity of multidrug resistant (MDR) Salmonella associated with cull cattle at harvest in the U.S. We found MDR Salmonella to be a consistently measurable subpopulation of the Salmonella present on hides and carcasses of cull cattle at harvest (16.7%, 11.7% and 0.33% on hides, pre-evisceration and post-intervention carcasses, respectively). Regional differences in MDR Salmonella prevalence were also observed. Extensive characterization of the Salmonella collected in this study revealed the existence of both epidemic (profiles found in multiple regions/seasons) and endemic clusters (profiles observed in limited regions/seasons) within several of the MDR serotypes examined.
Technical Abstract: The prevalence and diversity of multidrug resistant (MDR) Salmonella associated with cattle at harvest in the United States was examined. Hides and carcasses of cattle were sampled at processing plants (n=6) located in four geographically distant regions, from July 2005 to April 2006. Mean prevalence of Salmonella on hides, pre-evisceration (immediately after hide removal) and post-intervention (in the chiller and after the full complement of interventions) carcasses was 89.6%, 50.2% and 0.8%, respectively. MDR Salmonella (defined as those resistant to two or more antimicrobials) as a percent of Salmonella prevalence was 16.7% (95% CI 8.3 to 25.1), 11.7% (95% confidence interval [CI] 4.4 to 19.0) and 0.33% (95% CI -0.3 to 0.70), respectively. In this study, 16,218 Salmonella hide and carcass isolates were screened for antimocrobial resistance. Of these, 978 (6.0%) unique MDR Salmonella isolates were identified, serotyped and their XbaI PFGE profiles determined. The predominant MDR Salmonella serotypes observed were Newport (53.1%), Typhimurium (16.6%) and Uganda (10.9%). Differences in MDR Salmonella prevalence were detected and PFGE analysis revealed both epidemic clusters (profiles found in plants in multiple regions/seasons) and endemic clusters (profiles observed in plants in limited regions/seasons), within several of the MDR serotypes examined. Despite these differences, multiple-hurdle processing interventions employed at all plants were found to be quite effective and decreased Salmonella carcass contamination by 98.4% (95% CI 97.6 to 99.7).