Investigating multi-drug resistant Acinetobacter baumannii isolates at a tertiary hospital in Pretoria, South Africa

Purpose: Antimicrobial resistance is now globally recognised amongst the greatest threat to human health. Acinetobacter baumannii's' (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.

Methods: One hundred non repetitive isolates of A. baumannii were collected for the study. Antimicrobial susceptibility testing was performed using the VITEK2 system. The prevalence of antibiotic resistance associated genes and AdeABC efflux pump system were investigated using conventional PCR. Genetic relatedness of isolates was determined using rep-PCR.

Results: Seventy (70) of 100 isolates collected were confirmed multi-drug resistant and were bla_OXA51positive. Phenotypically, the isolates where resistant to almost all tested antibiotics. One isolate showed intermediate susceptibility to tigecycline while all were susceptible to colistin. Oxacillinase gene bla_OXA-23 was the most detected at 99% and only 1% was positive for bla_OXA-40. For Metallo-betalactamases (MBL), bla_VIMwas the most frequently detected at 86% and bla_SIM-1 at 3% was the least detected. Fifty-six isolates had the required gene combination for an active efflux pump. The most prevalent clone was clone A at 69% of the isolates. Colistin and tigecycline are the most effective against investigated isolates.

Conclusion: The major genotypic determinant for drug resistances is oxacillinases bla_OXA-23. The study reports for the first time, bla_OXA-40 and bla_SIM-1 detection in A. baumannii in South Africa.