Overexpression of bla OXA-58 Gene Driven by IS Aba3 Is Associated with Imipenem Resistance in a Clinical Acinetobacter baumannii Isolate from Vietnam

Abstract

The aim of this study was to investigate genetic structures and expression of bla _OXA-58 gene in five Acinetobacter baumannii clinical isolates recovered from two hospitals in southern Vietnam during 2012-2014. A. baumannii isolates were identified by automated microbiology systems and confirmed by PCR. All isolates were characterized as multidrug resistant by antimicrobial testing using the disk diffusion method. Four imipenem susceptible and one nonsusceptible isolates (MIC > 32 μg·ml^-1) were identified by E-test. PCR amplification of bla _OXA-58 gene upstream and downstream sequences revealed the presence of ISAba3 at both locations in one multidrug-resistant isolate. Semiquantitation of bla _OXA-51 and bla _OXA-58 gene expression was performed by the 2^-ΔΔCt method. The bla _OXA-51 gene expression of five isolates showed little difference, but the isolate bearing ISAba3-bla _OXA-58-ISAba3 exhibited significantly higher bla _OXA-58 mRNA level. Higher β-lactamases activity in periplasmic than cytoplasmic fraction was found in most isolates. The isolate overexpressing bla _OXA-58 gene possessed very high periplasmic enzyme activity. In conclusion, the A. baumannii isolate bearing ISAba3-bla _OXA-58 gene exhibited high resistance to imipenem, corresponding to an overexpression of bla _OXA-58 gene and very high periplasmic β-lactamase activity.