Dissemination of bla OXA-23 in Acinetobacter spp. in China: Main Roles of Conjugative Plasmid pAZJ221 and Transposon Tn 2009

Production of the OXA-23 carbapenemase is the most common reason for the increasing carbapenem resistance inAcinetobacter spp. This study was conducted to reveal the genetic basis ofbla OXA-23 dissemination inAcinetobacter spp. in China. A total of 63 carbapenem-resistant OXA-23-producingAcinetobacter sp. isolates, representing different backgrounds, were selected from 28 hospitals in 18 provinces for this study. Generally, two patterns of plasmids carryingbla OXA-23 were detected according to S1-nuclease pulsed-field gel electrophoresis and Southern blot hybridization. A ca. 78-kb plasmid, designated pAZJ221, was found in 23Acinetobacter baumannii and threeAcinetobacter nosocomialis isolates, while a novel ca. 50-kb plasmid was carried by only two otherA. baumannii isolates. Three of these isolates had an additional copy ofbla OXA-23 on 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 exceptbla OXA-23 . Thebla OXA-23 gene of the remaining 35 isolates was chromosome borne. Thebla OXA-23 genetic environments were correlated with Tn2009 in 57 isolates, Tn2008 in 5 isolates, and Tn2006 in 1 isolate. The MIC values for the carbapenems with these isolates were not significantly associated with the genomic locations or the copy numbers ofbla OXA-23 . Overall, these observations suggest that the plasmid pAZJ221 and Tn2009 have effectively contributed to the wide dissemination ofbla OXA-23 inAcinetobacter spp. in China and that horizontal gene transfer may play an important role in dissemination of thebla OXA-23 gene.