Emergence of Clinical Salmonella enterica Serovar Typhimurium Isolates with Concurrent Resistance to Ciprofloxacin, Ceftriaxone, and Azithromycin

Abstract

ABSTRACTSalmonellainfection is an important public health issue for which the needs of antimicrobial treatment are increasing. A total of 546 human clinicalS. entericaserovar Typhimurium isolates were recovered from patients in hospitals in China during the period of 2005 to ∼2011. Twenty percent of the isolates exhibited resistance to ciprofloxacin, and 4% were resistant to ceftriaxone. Importantly, for the first time, 12 (2%)S. Typhimurium isolates resistant to both ciprofloxacin and ceftriaxone were recovered; among these 12 isolates, two were also resistant to azithromycin, and one was resistant to all other drugs tested. The combined effects of various transferrable extended-spectrum β-lactamase determinants and a novel efflux-based ciprofloxacin resistance mechanism encoded by the mobile efflux geneoqxABwere responsible for the emergence of these extremely (highly) drug-resistant (XDR)S. Typhimurium isolates. The dissemination of resistance genes, such as those encoding ESBLs and the OqxAB pump, amongSalmonellaorganisms will speed up the selection of XDRSalmonella, posing a huge threat to public health andSalmonellainfection control.