Emergence of ISAba1-linked oxacillinase genes among carbapenem resistant Acinetobacter baumannii isolates in a tertiary cardiac center, Nepal

Insertion sequence contributes to the emergence of carbapenem resistance by dissemination of carbapenemase genes and providing promoter for their overexpression. This study aims to ascertain the occurrence of ISAba1-linked OXA carbapenemase genes and its relevance to carbapenem resistance level in Acinetobacter baumannii. This hospital based descriptive study was conducted at Shahid Gangalal National Heart Center, Kathmandu, Nepal. An overall of 1,291 clinical specimens received for routine culture and antibiotic susceptibility testing throughout the study period were included in this study. Identification of Acinetobacter baumannii was validated through detection of intrinsic blaOXA-51-like gene by polymerase chain reaction (PCR). Antibiotic susceptibility was tested by Kirby-Bauer disc diffusion approach and minimum inhibitory concentration (MIC) of meropenem was assessed through agar dilution method. Uniplex PCR assays were performed to detect genes encoding oxacillinases and ISAba1. Upstream association of insertion element, ISAba1 to oxacillinase genes was assessed through PCR mapping strategy using ISAba1F and OXA-51R/OXA-23R primers. Out of the 340 bacteria isolated, only 40 (11.8%) were Acinetobacter baumannii. All isolates were resistant against meropenem with MIC value ranging from 16-256 g/ml. blaOXA-23-like genes was present in every isolate but blaOXA-58 in just two isolates (5%). All isolates had ISAba1 either above blaOXA-23-like or blaOXA-51-like gene. Higher MIC90 value of meropenem (243.20 g/ml) was found in A. baumannii cluster with ISAba1-linked upstream to both blaOXA-23-like and blaOXA-51-like genes, thus depicting their eminent role to enhanced carbapenem resistance. Acinetobacter baumannii isolates with ISAba1-linked oxacillinase genes are rapidly emerging in clinical settings of Nepal. Thus, medical communities need to be prepared and enable targeted approaches for managing burgeoning problem of carbapenem resistance.