Species Distribution of Clinical <i>Acinetobacter</i> Isolates Revealed by Different Identification Techniques

<div><p>A total of 2582 non-duplicate clinical <i>Acinetobacter</i> spp. isolates were collected to evaluate the performance of four identification methods because it is important to identify <i>Acinetobacter</i> spp. accurately and survey the species distribution to determine the appropriate antimicrobial treatment. Phenotyping (VITEK 2 and VITEK MS) and genotyping (16S rRNA and <i>rpoB</i> gene sequencing) methods were applied for species identification, and antimicrobial susceptibility test of imipenem and meropenem was performed with a disk diffusion assay. Generally, the phenotypic identification results were quite different from the genotyping results, and their discrimination ability was unsatisfactory, whereas 16S rRNA and <i>rpoB</i> gene sequencing showed consistent typing results, with different resolution. Additionally, <i>A. pittii</i>, <i>A. calcoaceticus</i> and <i>A. nosocomialis</i>, which were phylogenetically close to <i>A. baumannii</i>, accounted for 85.5% of the non-<i>A. baumannii</i> isolates. One group, which could not be clustered with any reference strains, consisted of 11 isolates and constituted a novel <i>Acinetobacter</i> species that was entitled <i>genomic species 33YU</i>. None of the non-<i>A. baumannii</i> isolates harbored a <i>bla</i><sub>OXA-51</sub>-like gene, and this gene was disrupted by IS<i>Aba19</i> in only one isolate; it continues to be appropriate as a genetic marker for <i>A. baumannii</i> identification. The resistance rate of <i>non-A. baumannii</i> isolates to imipenem and/or meropenem was only 2.6%, which was significantly lower than that of <i>A. baumannii</i>. Overall, <i>rpoB</i> gene sequencing was the most accurate identification method for <i>Acinetobacter</i> species. Except for <i>A. baumannii</i>, the most frequently isolated species from the nosocomial setting were <i>A. pittii</i>, <i>A. calcoaceticus</i> and <i>A. nosocomialis</i>.</p></div>