Differences in phenotypic and genotypic characteristics among imipenem-non-susceptible Acinetobacter isolates belonging to different genomic species in Taiwan

In this study, we investigated the distribution of genes encoding various carbapenemases as well as their association with carbapenem resistance in clinical isolates of Acinetobacter genomic species from Taiwan. A total of 129 imipenem-non-susceptible and 79 imipenem-susceptible isolates were examined, of which 185 (88.9%) were Acinetobacter baumannii. Among the 185 A. baumannii isolates, imipenem non-susceptibility was more common in isolates with ISAba1–blaOXA-51-like (72/75; 96%), blaOXA-58-like (33/33; 100%) or blaOXA-24-like (7/7; 100%) than in isolates with only blaOXA-51-like (4/72; 5.6%). A metallo-β-lactamase (MBL) gene was present in two isolates of imipenem-resistant A. baumannii, and blaOXA-58-like was also present in these isolates. A total of 18% and 1% of imipenem-non-susceptible isolates of A. baumannii were resistant to tigecycline and colistin, respectively. Among the 23 isolates of non-baumannii Acinetobacter spp., blaOXA-58-like and MBL genes were widely disseminated in the imipenem-resistant isolates, and isolates with blaOXA-58-like and MBL genes had higher imipenem minimum inhibitory concentrations than those with blaOXA-58-like alone. Although the rate of non-susceptibility to colistin was 26.7% among the imipenem-non-susceptible isolates of non-baumanniiAcinetobacter, 93.3% and 100% were susceptible to ciprofloxacin and tigecycline, respectively. In conclusion, different isolates of imipenem-non-susceptible A. baumannii and non-baumanniiAcinetobacter contained different carbapenemases and had different antimicrobial susceptibilities.