Acquisition of a Plasmid-Borne bla OXA-58 Gene with an Upstream IS 1008 Insertion Conferring a High Level of Carbapenem Resistance to Acinetobacter baumannii

The oxacillinase gene was reported to confer limited resistance to carbapenem in Acinetobacter baumannii . In this study, we have demonstrated that an A. baumannii clinical isolate harboring a plasmid, pTVICU53, has 11,037 bp encoding 13 open reading frames. A bla OXA-58 gene with an upstream insertion of truncated IS Aba3 (ΔIS Aba3 ) and IS 1008 was found in this plasmid. ΔIS Aba3 and IS 1008 provided two independent promoters for the transcription control of the bla OXA-58 gene. The transformation of pTVICU53 or a shuttle vector bearing IS 1008 -ΔIS Aba3 - bla OXA-58 to different A. baumannii recipients can increase their MICs of carbapenem 64- to 256-fold. The deletion of promoters provided by IS 1008 resulted in dramatic decreases in bla OXA-58 transcription and a 32- to 64-fold reduction in the carbapenem MIC. These findings highlight that A. baumannii might develop carbapenem resistance with a single transformation step, taking up a plasmid containing a genetic construct with a potentially high level of transcription of the bla OXA-58 gene.