Abstract
This study investigated the molecular epidemiology of carbapenem-resistant Acinetobacter nosocomialis and Acinetobacter pittii (ANAP). Clinical isolates of Acinetobacter spp. collected by the biennial nationwide Taiwan Surveillance of Antimicrobial Resistance program from 2010 to 2014 were subjected to species identification, antimicrobial susceptibility testing, and PCR for detection of carbapenemase genes. Whole-genome sequencing or PCR mapping was performed to study the genetic surroundings of the carbapenemase genes. Among 1,041 Acinetobacter isolates, the proportion of ANAP increased from 11% in 2010 to 22% in 2014. The rate of carbapenem resistance in these isolates increased from 7.5% (3/40) to 22% (14/64), with a concomitant increase in their resistance to other antibiotics. The blaOXA-72 and blaOXA-58 genes were highly prevalent in carbapenem-resistant ANAP. Various genetic structures were found upstream of blaOXA-58 in different plasmids. Among the plasmids found to contain blaOXA-72 flanked by XerC/XerD, pAB-NCGM253-like was identified in 8 of 10 isolates. Conjugations of plasmids carrying blaOXA-72 or blaOXA-58 to A. baumannii were successful. In addition, three isolates with chromosome-located blaOXA-23 embedded in AbGRI1-type structure with disruption of genes other than comM were detected. Two highly similar plasmids carrying class I integron containing blaIMP-1 and aminoglycoside resistance genes were also found. The universal presence of blaOXA-272/213-like on A. pittii chromosomes and their lack of contribution to carbapenem resistance indicate its potential to be a marker for species identification. The increase of ANAP, along with their diverse mechanisms of carbapenem resistance, may herald their further spread and warrants close monitoring.
Highlights
This study investigated the molecular epidemiology of carbapenemresistant Acinetobacter nosocomialis and Acinetobacter pittii (ANAP)
A. baumannii has been the focus of most studies, and relatively few studies have been conducted on A. nosocomialis and A. pittii, perhaps due to their low prevalence and low rates of resistance in the past few decades
The percentages of A. baumannii, A. nosocomialis, and A. pittii determined by gyrB typing, and their antibiograms are shown in Fig. 1a and Tables S1 and S2
Summary
This study investigated the molecular epidemiology of carbapenemresistant Acinetobacter nosocomialis and Acinetobacter pittii (ANAP). The distribution of A. baumannii, A. nosocomialis, and A. pittii varied among Acb complex isolates from clinical samples in different geographic regions. The present study found that in 2010, 2012, and 2014, the rates of resistance to carbapenems (imipenem and meropenem) remained stable at 65.4, 76.5, and 65.5% in A. baumannii, but increased from 4.5 to 9.3% to 25.8% in A. pittii and from 11.1 to 26.7% to 18.2% in A. nosocomialis, respectively (Fig. 1b).
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