Molecular characterisation of multiple drug-resistant Acinetobacter baumannii isolates in southern Taiwan

The purpose of this study was to develop a multiplex polymerase chain reaction (mt-PCR) assay for synchronous detection of carbapenem resistance genes and/or pandrug resistance genes in clinical isolates of multidrug-resistant Acinetobacter baumannii (MDR-AB) and to investigate the association between the genetic make-up and a drug-resistant pattern. In total, 213 MDR-AB isolates were collected. All clinical isolates underwent antimicrobial susceptibility testing and were analysed for the presence of oxacillinase genes (bla(OXA-23), bla(OXA-24), bla(OXA-51)-like and bla(OXA-58)), class A and C β-lactamase genes (bla(TEM-1) and bla(AmpC), respectively), and an integron-associated antibiotic resistance gene (int1) by an in-house-designed mt-PCR assay. Of the 213 isolates, 73.87% harboured both bla(TEM-1) and bla(AmpC) and 83.92% carried at least three oxacillinase genes. Moreover, 64.82% of the isolates were significant in that they had two β-lactamase genes and three oxacillinase genes (P<0.001), indicating the complexity of the genetic make-up of carbapenem-resistant A. baumannii. The bla(OXA-51)-like allele was detected in the majority of these A. baumannii isolates (97.49%), whereas bla(OXA-23) was rarely prevalent in these isolates. In multivariate logistic regression, the presence of bla(OXA-23) and bla(TEM-1) had a statistically significant association with imipenem resistance [bla(OXA-23), P=0.004, odds ratio (OR)=10.52, 95% confidence interval (CI) 2.12-52.17; bla(TEM-1), P=0.005, OR=6.14, 95% CI 1.74-21.62]. These results suggest that detecting bla(OXA-23) and bla(TEM-1) genes could be used to predict imipenem resistance in MDR-AB isolates. A mt-PCR for detecting carbapenem resistance genes and pandrug resistance genes of A. baumannii isolates was developed to provide an assay to quickly screen for potential imipenem-resistant A. baumannii in the clinic.