Plasmid-mediated Quinolone Resistance among Non-TyphiSalmonella entericaIsolates, USA

We determined the prevalence of plasmid-mediated quinolone resistance mechanisms among non-Typhi Salmonella spp.isolated from humans, food animals, and retail meat in the United States in 2007.Six isolates collected from humans harbored aac(6′)Ib-cr or a qnr gene.Most prevalent was qnrS1.No animal or retail meat isolates harbored a plasmid-mediated mechanism.S evere Salmonella enterica infections are commonly treated with fluoroquinolones (e.g., ciprofloxacin) (1).In the United States, the antimicrobial drug susceptibility of Salmonella spp.isolated from humans, food animals, and retail meats is systematically monitored by the National Antimicrobial Resistance Monitoring System (NARMS).This program is a collaborative effort of the Centers for Disease Control and Prevention (CDC), the Food and Drug Administration Center for Veterinary Medicine (FDA-CVM) and the US Department of Agriculture (USDA).Antimicrobial susceptibility to fluoroquinolones among Salmonella spp.has been monitored since the program's inception in 1996.Although fluoroquinolone resistance in Enterobacteriaceae is predominantly due to topoisomerase mutations, 3 plasmid-mediated mechanisms have been described that confer decreased susceptibility to ciprofloxacin: quinolone resistance proteins (Qnr), Aac(6′)-Ib-cr, and QepA efflux (2).