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ARS Home » Research » Publications at this Location » Publication #323375
Title: Antimicrobial susceptibility and plasmid replicon typing of Salmonella enterica serovar Kentucky isolates recovered from broilers

Author
item LADELY, SCOTT - Food Safety Inspection Service (FSIS)
item Meinersmann, Richard - Rick
item BALL, TAKIYAH - Former ARS Employee
item FEDORKA-CRAY, PAULA - Former ARS Employee

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2016
Publication Date: 6/14/2016
Citation: Ladely, S.R., Meinersmann, R.J., Ball, T.A., Fedorka-Cray, P.J. 2016. Antimicrobial susceptibility and plasmid replicon typing of Salmonella enterica serovar Kentucky isolates recovered from broilers. Foodborne Pathogens and Disease. 13(6):309-315.

Interpretive Summary: There are thousands of types of Salmonella, but one type, serotype Kentucky, has become very common in chickens in the last 20 years. The percent of isolates of this type that are antimicrobial resistant has also increased in that time period. We analyzed isolates to determine the probable ancestry patterns and determine if the antimicrobial resistance contributed to the increase in prevalence. Ancestry was analyzed by clustering sub-types that were determine by pulsed-field gel electrophoresis, a method that detects changes in the structure of the chromosome. We also tested for the presence of plasmids, extra-chromosomal pieces of DNA that are frequently transferred between strains in nature and often carry genes for antimicrobial resistance with them. The ancestry pattern correlated with the incorporation of a specific type of plasmid known as replicon type FIB. However, the ancestry showed that there were factors other than the antimicrobial resistance that promoted the increased prevalence of the seroype and antimicrobial resistance was a so-called "hitch-hiker."

Technical Abstract: Salmonella Kentucky has become the predominate serotype recovered from broiler slaughter in the United States and the prevalence of antimicrobial resistance (AMR) has increased dramatically in this serotype. Relationships between AMR, genotype, and plasmid replicon types were characterized for 600 S. Kentucky isolated from chicken carcasses from 2004 to 2013. Pulsed-field gel electrophoresis cluster analysis revealed 112 types sharing 73.0% similarity. Two large clusters comprised over half of the isolates studied. The largest (190 isolates) cluster had significantly more (p<0.05) streptomycin (68.9%) and tetracycline (92.1%) resistance compared to the other major (144 isolates) cluster (11.8% and 13.2% for streptomycin and tetracycline, respectively) or the remainder of the isolates examined (49.2% and 39.8% for streptomycin and tetracycline, respectively). Plasmid replicon type FIB was linked (p<0.05) to streptomycin and tetracycline resistance and type HI2 was linked (p<0.05) to streptomycin resistance. We conclude that the dramatic increase in streptomycin and tetracycline resistance among S. Kentucky isolated from poultry is due to the clonal expansion of strains harboring plasmid replicon types FIB and HI2.