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 (blaOXA-23, blaOXA-24, blaOXA-51-like and blaOXA-58), class A and C β-lactamase genes (blaTEM-1 and blaAmpC, 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 blaTEM-1 and blaAmpC 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 blaOXA-51-like allele was detected in the majority of these A. baumannii isolates (97.49%), whereas blaOXA-23 was rarely prevalent in these isolates. In multivariate logistic regression, the presence of blaOXA-23 and blaTEM-1 had a statistically significant association with imipenem resistance [blaOXA-23, P = 0.004, odds ratio (OR) = 10.52, 95% confidence interval (CI) 2.12-52.17; blaTEM-1, P = 0.005, OR = 6.14, 95% CI 1.74-21.62]. These results suggest that detecting blaOXA-23 and blaTEM-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.