Emergence of ISAba1-linked oxacillinase genes among carbapenem resistantAcinetobacter baumanniiisolates 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 IS Aba1 -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 bla OXA-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 IS Aba1 . Upstream association of insertion element, IS Aba1 to oxacillinase genes was assessed through PCR mapping strategy using IS Aba1 F 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 μg/ml. bla OXA-23-like genes was present in every isolate but bla OXA-58 in just two isolates (5%). All isolates had IS Aba1 either above bla OXA-23-like or bla OXA-51-like gene. Higher MIC 90 value of meropenem (243.20 μg/ml) was found in A . baumannii cluster with IS Aba1 -linked upstream to both bla OXA-23-like and bla OXA-51-like genes, thus depicting their eminent role to enhanced carbapenem resistance. Acinetobacter baumannii isolates with IS Aba1 -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.