Complete genome sequence of Acinetobacter baumannii MDR-TJ and insights into its mechanism of antibiotic resistance.

OBJECTIVES To determine the genome sequence of Acinetobacter baumannii strain MDR-TJ and characterize the mechanisms of multidrug resistance in this strain. METHODS The whole-genome sequence was determined using Roche 454 GS FLX Titanium. Subsequently, the gaps were closed by sequencing PCR products. The genome of strain MDR-TJ was annotated using IMG ER, the RAST annotation server and the BASys bacterial annotation system. The comM gene of MDR-TJ was examined to identify a possible antibiotic resistance island. Based on the results of multilocus sequence typing, we investigated seven multidrug-resistant A. baumannii strains belonging to global clone 2 (GC2) isolated from Asia, Australia and Europe to determine the backbone shared by resistance islands of GC2 isolates. RESULTS The A. baumannii strain MDR-TJ genome consists of a circular chromosome and a plasmid, pABTJ1. Strain MDR-TJ was assigned to sequence type ST2. Strain MDR-TJ harbours a 41.6 kb resistance island designated RI(MDR-TJ), which can be derived from the backbone of Tn6167 through the insertion of a Tn6022 into the 3'-end of the tetA(B) gene. Comparative analysis showed that transposon Tn6022 and its truncated forms prevailed in the antibiotic resistance islands of GC2 isolates. The carbapenem resistance gene bla(OXA-23) carried by transposon Tn2009 is located on a putatively conjugative plasmid, pABTJ1. CONCLUSIONS A. baumannii strain MDR-TJ belongs to GC2 and is resistant to multiple antibiotics. A. baumannii MDR-TJ harbours a genomic resistance island that interrupts the comM gene. The carbapenem resistance of MDR-TJ is mediated by a putatively conjugative plasmid, pABTJ1.