Multiplication of blaOXA-23 is common in clinical Acinetobacter baumannii, but does not enhance carbapenem resistance

Abstract

Objectives: To investigate the copy number of blaOXA-23 and its correlation with carbapenem resistance in carbapenem-resistant Acinetobacter baumannii (CRAB). Methods: A total of 113 blaOXA-23-positive clinical CRAB isolates were collected from two hospitals in Zhejiang province, China. Their genetic relatedness was determined by MLST. The MIC of imipenem was determined using the agar diffusion method and the copy number of blaOXA-23 was measured using quantitative real-time PCR (qRT-PCR). The complete genomes of five clinical CRAB strains were sequenced using PacBio technology to investigate the multiplication mechanism of blaOXA-23. Results: Most of the isolates (100/113) belonged to global clone II and the MIC of imipenem ranged from 16 to 96 mg/L. The gene blaOXA-23 resided exclusively in Tn2006 or Tn2009. Approximately 38% of the isolates carried two or more copies of blaOXA-23. The copy number of blaOXA-23 was not correlated with the MIC of imipenem. Within the five sequenced strains, multiple copies of blaOXA-23 were either tandemly clustered or independently inserted at different genomic sites. Conclusions: Multiplication of blaOXA-23 is common in CRAB, but does not enhance carbapenem resistance. Multiplication can be present in the form of either tandem amplifications or independent insertions at different sites.