Molecular Epidemiology and Mechanisms of Tigecycline Resistance in Clinical Isolates of Acinetobacter baumannii from a Chinese University Hospital
ABSTRACTBecause of its remarkable ability to acquire antibiotic resistance and to survive in nosocomial environments,Acinetobacter baumanniihas become a significant nosocomial infectious agent worldwide. Tigecycline is one of the few therapeutic options for treating infections caused byA. baumanniiisolates. However, tigecycline resistance has increasingly been reported. Our aim was to assess the prevalence and characteristics of efflux-based tigecycline resistance in clinical isolates ofA. baumanniicollected from a hospital in China. A total of 74A. baumanniiisolates, including 64 tigecycline-nonsusceptibleA. baumannii(TNAB) and 10 tigecycline-susceptibleA. baumannii(TSAB) isolates, were analyzed. The majority of them were determined to be positive foradeABC,adeRS,adeIJK, andabeM, while theadeEgene was found in only one TSAB isolate. Compared with the levels in TSAB isolates, the mean expression levels ofadeB,adeJ,adeG, andabeMin TNAB isolates were observed to increase 29-, 3-, 0.7-, and 1-fold, respectively. The efflux pump inhibitors (EPIs) phenyl-arginine-β-naphthylamide (PAβN) and carbonyl cyanide 3-chlorophenylhydrazone (CCCP) could partially reverse the resistance pattern of tigecycline. Moreover, thetetX1gene was detected in 12 (18.8%) TNAB isolates. To our knowledge, this is the first report of thetetX1gene being detected inA. baumanniiisolates. ST208 and ST191, which both clustered into clonal complex 92 (CC92), were the predominant sequence types (STs). This study showed that the active efflux pump AdeABC appeared to play important roles in the tigecycline resistance ofA. baumannii. The dissemination of TNAB isolates in our hospital is attributable mainly to the spread of CC92.