Dissemination of bla OXA - 23 in Acinetobacter spp . in China : main roles of 1 conjugative plasmid pAZJ 221 and transposon Tn 2009

15 Production of OXA-23 carbapenemase is the most common reason for the increasing 16 carbapenem resistance in Acinetobacter spp. This study was conducted to reveal the genetic 17 basis of the blaOXA-23 dissemination in Acinetobacter spp. in China. A total of sixty-three 18 carbapenem-resistant OXA-23-producing Acinetobacter spp. isolates, representing different 19 backgrounds, were selected from 28 hospitals of 18 provinces for this study. Generally, two 20 patterns of plasmids carrying blaOXA-23 were detected according to S1-PFGE and Southern 21 hybridization. A ca.78kb plasmid, designated as pAZJ221, was found in twenty-three A. 22 baumannii and three A. nosocomialis isolates while a novel ca.50kb plasmid carried by only 23 two other A. baumannii isolates. Three isolates of them had an additional copy of blaOXA-23 on 24 chromosome. Transformation of both plasmids succeeded but only pAZJ221 was conjugative. 25 Plasmid pAZJ221 was sequenced completely and found to carry no other previously known 26 resistance genes except blaOXA-23. The blaOXA-23 gene of the remaining 35 isolates was 27 chromosome-borne. The blaOXA23 genetic environments were correlated with Tn2009, Tn2008 28 and Tn2006 in 57, 5 and one isolates, respectively. The MIC levels of carbapenems of these 29 isolates were not significantly associated with the genomic locations or the copy numbers of 30 blaOXA-23. Overall, these observations suggest that plasmid pAZJ221 and Tn2009 have 31 effectively contributed to the wide dissemination of blaOXA-23 in Acinetobacter spp. in China 32 and horizontal gene transfer may play an important role in the dissemination of blaOXA-23 gene. 33