Dissemination ofblaOXA-23in Acinetobacter spp. in China: Main Roles of Conjugative Plasmid pAZJ221 and Transposon Tn2009

Abstract

ABSTRACTProduction of the OXA-23 carbapenemase is the most common reason for the increasing carbapenem resistance inAcinetobacterspp. This study was conducted to reveal the genetic basis ofblaOXA-23dissemination inAcinetobacterspp. in China. A total of 63 carbapenem-resistant OXA-23-producingAcinetobactersp. isolates, representing different backgrounds, were selected from 28 hospitals in 18 provinces for this study. Generally, two patterns of plasmids carryingblaOXA-23were detected according to S1-nuclease pulsed-field gel electrophoresis and Southern blot hybridization. A ca. 78-kb plasmid, designated pAZJ221, was found in 23Acinetobacter baumanniiand threeAcinetobacter nosocomialisisolates, while a novel ca. 50-kb plasmid was carried by only two otherA. baumanniiisolates. Three of these isolates had an additional copy ofblaOXA-23on the chromosome. Transformation of the two plasmids succeeded, but only pAZJ221 was conjugative. Plasmid pAZJ221 was sequenced completely and found to carry no previously known resistance genes exceptblaOXA-23. TheblaOXA-23gene of the remaining 35 isolates was chromosome borne. TheblaOXA-23genetic environments were correlated with Tn2009in 57 isolates, Tn2008in 5 isolates, and Tn2006in 1 isolate. The MIC values for the carbapenems with these isolates were not significantly associated with the genomic locations or the copy numbers ofblaOXA-23. Overall, these observations suggest that the plasmid pAZJ221 and Tn2009have effectively contributed to the wide dissemination ofblaOXA-23inAcinetobacterspp. in China and that horizontal gene transfer may play an important role in dissemination of theblaOXA-23gene.