Application of Multiplex PCR for the Identification of Oxacillinase Genes and Determination of Antibiotic Resistance Pattern in Environmental Isolates of Acinetobacter baumannii in ICU

Acinetobacter baumannii is a common cause of nosocomial infections. A prominent feature of these bacteria is resistance to carbapenems. This study aimed to identify OXA genes encoding oxacillinase in Acinetobacter baumannii isolates.

This cross-sectional descriptive study was performed on 25 environmental A. baumannii isolates collected from ICU over 8 months. Definitive identification of isolates was performed by biochemical tests and polymerase chain reaction (PCR) of 16s rRNA gene. Antibiotic susceptibility testing was performed on Müller- Hinton agar medium by disk diffusion and E-test. Antibiogram and multiplex PCR data of beta-lactamase genes were collected and analyzed at a significance level of P < 0.05 using SPSS 22.0.

Except for one isolate, all isolates (96%) were sensitive to polymyxin B and 80% of isolates were sensitive to oxacillin. All isolates were sensitive to meropenem, ampicillin/sulbactam, gentamicin, amikacin, piperacillin, and carbenicillin. The results showed that 25 isolates (100%) had OXA-51 gene, 21 isolates (84%) had OXA-58 gene, one isolate (4%) had OXA-24 gene, and none of the isolates contained OXA-23 gene. Only isolate No.10 had three oxacillinase genes simultaneously and it was resistant to oxacillin, polymyxin B, and cephalothin.

The study showed that environmental isolates of ICU do not have pathogenic genes present in the clinical isolates, and how these genes are transferred to the peripheral isolates is an important point that should be studied. Identification of genes encoding carbapenem resistance may help to understand the mechanisms of resistance transfer in A. baumannii. The lack of the OXA-23 gene plays an important role in the susceptibility of isolates to antibiotics and non-emergence of resistant strains.