Decoding Carbapenem Resistance: Detection of Carbapenemase Genes in Clinical Isolates of Carbapenem-Resistant Acinetobacter baumannii

Introduction Acinetobacter baumannii is a common nosocomial pathogen that has developed multidrug resistance (MDR) to different classes of antibiotics, including carbapenems. The World Health Organization has declared carbapenem-resistant A. baumannii (CRAB) a critical priority pathogen. Aims and objective This study aimed to determine the antimicrobial susceptibility of CRAB, identify carbapenemase production, and detect carbapenemase genes in clinical isolates of CRAB. Methods This study was conducted in the Department of Microbiology, Himalayan Institute of Medical Sciences and School of Biosciences, Swami Rama Himalayan University, Dehradun. Antimicrobial susceptibility and identification were performed by the VITEK-2 automated system (bioMérieux, Marcy-l'Étoile, France). Carbapenemase production was determined by using the combined disc test (CDT) method. These isolates were genetically screened for carbapenemase genes. Results A total of 100 CRAB isolates were included in the study. All 100 (100%) isolates were resistant to β-lactam/β-lactamase inhibitor combinations, cephalosporins, fluoroquinolones, and aminoglycosides. The highest sensitivity was observed for minocycline (15/100, 15%), followed by cotrimoxazole. Phenotypic detection of carbapenemase production was carried out using the CDT, followed by molecular confirmation through polymerase chain reaction (PCR). Carbapenemase production was observed in 97 (97%) of CRAB isolates. blaOXA-51, blaNDM-1, blaOXA-23, and blaVIM were detected in 100 (100%), 94 (94%), 88 (88%), and 70 (70%) of isolates, respectively. Coexistence of blaNDM-1 and blaOXA-23 (83, 83%) as well as blaNDM-1 and blaVIM (65, 65%) among CRAB isolates was a notable finding in our study. The relationship between the presence of carbapenemase genes and antibiotic susceptibility test results was evaluated using the chi-square test, with p-values <0.05 considered statistically significant. Conclusion In our study, CRAB isolates demonstrated high resistance to antimicrobial agents, with limited sensitivity to minocycline and cotrimoxazole. The coexistence of multiple carbapenemase genes, including blaNDM-1, blaOXA-23, and blaVIM, reflects significant genetic diversity and enhances the potential for horizontal gene transfer and rapid dissemination within healthcare settings. Such high-level gene coexistence has important clinical and epidemiological implications, as it may contribute to treatment failure and hospital outbreaks. This finding emphasizes the critical need for strict infection control measures, antimicrobial stewardship programs, and continuous molecular surveillance of resistance determinants to limit the spread of these MDR organisms.