Genetic Diversity of OXA-like Genes in Multidrug-Resistant Acinetobacter baumannii Strains from ICUs

This study aimed to investigate the genetic diversity of OXA-51-like, OXA-23-like, OXA-24, and OXA-58-like genes and the role of β-lactamases in carbapenem resistance among multidrug resistant Acinetobacter baumannii strains recovered from patients in intensive care units (ICUs).

Non-duplicate clinical isolates of A. baumannii from ICUs that were identified as imipenem and meropenem resistant were collected. Antimicrobial susceptibilities were determined by PhoenixTM system (Becton Dickinson, USA). Minimum inhibitory concentrations (MICs) for imipenem and meropenem were determined by using gradient strip method (E-test) and interpreted according to CLSI. Presence of carbapenemase activity was determined by the modified Hodge test (MHT) and detection of metallo-β-lactamase (MBL) was performed by the double-disk synergy test (DDST) and MBL E-test. Detection of the four groups of OXA carbapenemase genes (OXA-23, OXA-24, OXA-51, and OXA-58) was carried out using a multiplex PCR assay. Sequencing of the products in both directions was performed by ABI 3130XL genetic analyzer (Life Technologies Corporation, CA, USA). The resulting DNA sequence was analyzed by the BLAST program, available at the NCBI website.

Sixty-one non-duplicate, multidrug resistant clinical A. baumannii isolates were studied. MHTs were positive for all 61 A. baumannii strains, but none of them showed MBL activity. As determined through multiplex PCR, all of the 61 isolates had blaOXA-51 genes including blaOXA-64, blaOXA-66, and blaOXA-91, 50 isolates had blaOXA-23, and 11 isolates had blaOXA-58 genes. Alleles encoding OXA-24-like enzymes were not detected in any isolates.

This study indicated that the major cause of carbapenem resistance in our region was OXA-type car-bapenemase encoded by blaOXA-51, blaOXA-23, and blaOXA-58 genes and as we know, this is the first report from Turkey identifying blaOXA-51-like sequences.