Genetic determinants of multi-drug resistance in Acinetobacter baumannii at an academic hospital in Pretoria, South Africa

Abstract

Antimicrobial resistance is now globally recognised as the greatest threat to human health. Acinetobacter baumanniis (A. baumannii) clinical significance has been driven by its ability to obtain and transmit antimicrobial resistance factors. In South Africa, A. baumannii is a leading cause of healthcare associated infections (HAI). In this study, we investigated the genetic determinants of multi-drug resistant A. baumannii (MDRAB) at a teaching hospital in Pretoria, South Africa.\n\nOne hundred non repetitive isolates of A. baumannii were collected for the study at Dr George Mukhari Tertiary Laboratory (DGMTL). Antimicrobial susceptibility testing was performed using the VITEK2 system (bioMerieux, France). The prevalence of common resistance associated genes and AdeABC efflux pump system associated genes were investigated using conventional PCR. Genetic relatedness of isolates was then determined using rep-PCR.\n\nSeventy (70) of 100 isolates collected were confirmed to be multi-drug resistant and were blaOXA51 positive. Phenotypically, the isolates where resistant to almost all tested antibiotics. However, one isolate showed intermediate susceptibility to tigecycline while all were susceptible to colistin. Oxacillinase encoding gene blaOXA-23 was the most detected at 99% and only 1% was positive for blaOXA-40. The PCR results for metallo-betalactamase (MBL) encoding genes showed that MBL blaVIM was the most frequently detected at 86% and blaSIM-1 at 3% was the least detected. Out of 70 isolates, 56 isolates had the required gene combination for an active efflux pump. The most prevalent clone was clone A at 69% of the isolates. Regarding treatment; colistin and tigecycline are the most effective against strains encountered at DGMTL as all tested carbapenems seem to have lost their effectiveness.\n\nThe major genotypic determinants for drug resistances are oxacillinases: blaOXA-51 (100%) and blaOXA-23 (99%). The study reports for the first time, blaOXA-40 and blaSIM-1 detection in A. baumannii in South Africa.