Location: Meat Safety & Quality Research
Title: Diversity of Multi-drug Resistant Salmonella enterica Associated with Cull Cattle at Harvest in the United States Authors
|Koohmaraie, Mohammad -|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 21, 2010
Publication Date: June 8, 2010
Citation: Harhay, D.M., Poole, T.L., Durso, L.M., Arthur, T.M., Bosilevac, J.M., Kalchayanand, N., Shackelford, S.D., Wheeler, T.L., Koohmaraie, M. 2010. Diversity of Multi-drug Resistant Salmonella enterica Associated with Cull Cattle at Harvest in the United States [abstract]. American Society for Microbiology. p. 25, Presentation No. S4:1 and p. 111, Poster No. B176. Technical Abstract: Background: 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 multi-drug resistant (MDR) Salmonella associated with cull cattle at harvest in the U.S. Methods: Hide (1000 cm**2) and carcass swabs (8000 cm**2) of 3,040 cattle were collected from cattle at harvest in four geographically distant regions, from July 2005 to April 2006. In all, 16,218 Salmonella were isolated from 10,630 hide and carcass samples. All isolates were screened for drug resistance and 978 (6.0%) MDR Salmonella isolates were characterized. Antimicrobial susceptibility testing was performed using the Sensititre Broth Microdilution System (TREK Diagnostic Systems) and CMV1AGNF test plates. All MDR Salmonella were serotyped and their XbaI PFGE profiles determined. Plasmid profiles were determined for a representative subset of MDR Salmonella (n=188) which were further assayed for the presence of 18 plasmid replicon regions as described by Carattoli et al. (2005 J. Microbiol. Methods 63:219–228). Mating experiments with E. coli recipients (JM109 and DH5alpha) were performed with a subset of isolates to examine plasmid and resistance determinant transfer. Results: Salmonella mean prevalence on hides, pre-evisceration and post-intervention carcasses was 89.6% (95% confidence interval [CI] 85.1 - 94.0), 50.2% (95% CI 40.9 - 59.5) and 0.8% (95% CI 0.18 - 1.42), respectively, while MDR Salmonella, as a percent of Salmonella prevalence was 16.7% (95% CI 8.3 - 25.1), 11.7% (95% CI 4.4 - 19.0) and 0.33% (95% CI -0.3 - 0.70). Predominant MDR Salmonella serotypes observed were Newport (53.1%), Typhimurium (16.6%) and Uganda (10.9%), and IncA/C and IncN were the predominant plasmid replicon types identified. Conclusions: MDR Salmonella were found to be a consistently measurable subpopulation of the Salmonella present on hides and carcasses of cull cattle at harvest. Regional differences in MDR Salmonella prevalence were detected, and analysis of PFGE profiles, antimicrobial resistance phenotypes and plasmid replicon types 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.