Distribution of carbapenem resistance determinants among epidemic and non-epidemic types of Acinetobacter species in Japan

We performed a comparative molecular analysis on three types of clinically isolated Acinetobacter spp.: epidemic sequence types (STs) of Acinetobacter baumannii (epidemic STAB), non-epidemic sequence types of A. baumannii (non-epidemic ST-AB) and non-baumannii Acinetobacter spp. A total of 87 isolates - 46 A. baumannii, 25 A. pittii and 16 A. nosocomialis - from 43 hospitals were analysed. Of these, 31 A. baumannii isolates were ST1 or ST2 according to the Pasteur Institute multilocus sequence typing scheme and were defined as epidemic ST-AB. The other 15 A. baumannii isolates were defined as non-epidemic ST-AB. The epidemic ST-AB isolates harboured the bla_OXA-23-like gene or had an ISAba1 element upstream of bla_OXA-51-like, or both, whereas non-epidemic ST-AB and non-baumannii Acinetobacter spp. isolates harboured bla_OXA-58-like or metallo-β-lactamase genes, or both. The proportion of multidrug-resistant isolates was significantly higher in the epidemic ST-AB isolates (48%) than that in the other types of Acinetobacter isolates (5 %) (P,0.05). In addition, epidemic ST-AB isolates exhibited a relatively higher proportion of fluoroquinolone resistance. We demonstrated that, in terms of genotypes and phenotypes of antimicrobial resistance, non-epidemic ST-AB isolates shared more similarity with non-baumannii Acinetobacter spp. isolates than with epidemic ST-AB isolates, regardless of bacterial species. In addition, this study revealed that, even in Japan, where IMP-type metallo-β-lactamase producers are endemic, epidemic ST-AB harbouring bla_IMP have not yet emerged.