MOLECULAR EPIDEMIOLOGY OF METALLO BETA LACTAMASES IN ACINETOBACTER BAUMANNII AT A TERTIARY CARE HOSPITAL

Abstract

Background: Carbapenem resistance mediated by metallo beta lactamases (MBL) in Acinetobacter baumannii is a global challenge due to its rapid spread and limited therapeutic options.
 Objective: To determine the prevalence of MBL in A. baumannii isolates in hospitalized patients by both phenotypic and genotypic methods.
 Materials and Methods: The clinical samples were collected from inpatients and subcultured on routine culture media for growth. Identification of bacteria along with antimicrobial sensitivity testing was done by VITEK -2 Compact (bioMerieux). Antibiotics that were not tested by VITEK-2 were tested manually by Kirby-Bauer disk diffusion method according to CLSI 2017 and EUCAST 2016 guidelines. The isolates which were resistant to carbapenem (imipenem and/ or meropenem) were tested by phenotypic (imipenem-EDTA combined disk method) and genotypic method for presence of common metallo beta lactamases genes (blaIMP, blaNDM, blaGIM, blaVIM, blaSPM and blaSIM).
 Results: 84 non duplicate A.baumannii were isolated out of 947 pathogenic gram negative isolates. Majority (47.6%) of isolates were obtained from tracheostomy/endotracheal/bronchoalveolar lavage (TT/ET/BAL) followed by sputum (21.4%). None of the isolates were found to be resistant to colistin and tigecycline. 73 (86.9%) isolates were found to be carbapenem resistant, among these 60 (82.2%) were found to be MBL positive by phenotypic and 32 (43.2%) by genotypic method. MBL genes detected were blaNDM (39.7%), blaGIM (2.7%) and blaVIM (1.4%). None of the isolates were positive for blaIMP, blaSPM and blaSIM.
 Conclusion: The prevalence of MBL in carbapenem resistant isolates of A.baumannii was 87.7%. blaNDM was the most common gene detected. No significant difference was found in the ability of phenotypic and genotypic methods for MBL detection. The resistance rate of the A.baumannii is high for most antibiotics except for polymyxins (E&B) and tigecycline.
 Key words: Metallo beta Lactamases, Acinetobacter baumannii, Carbapenem.