Phenotypic and molecular characterization of carbapenem resistance among clinical isolates of Pseudomonas aeruginosa and Acinetobacter baumannii

Abstract Background Carbapenem-resistant Pseudomonas aeruginosa (CRPA) and Acinetobacter baumannii (CRAB) were listed on the WHO bacterial priority pathogens list in 2017. These gram-negative bacteria often cause healthcare-associated infections (HAIs), which pose an increasing threat to public health. This study aimed to isolate and identify CRPAs and CRABs from a tertiary care hospital in central Nepal and characterize carbapenem resistance genes at the molecular level. Materials and methods A total of 59 isolates, including 27 Pseudomonas aeruginosa and 32 Acinetobacter baumannii , were collected from different clinical samples from April 2021 to December 2022. Antibiotic susceptibility was determined via the Kirby disc diffusion method. The modified carbapenem inactivation method (mCIM) was used for phenotypic confirmation of carbapenem resistance. Conventional polymerase chain reaction (PCR) was used to detect carbapenem resistance genes. Results Among the 59 isolates, 76.3% were multidrug resistant (MDR), 63.0% were extended-spectrum beta-lactamase (ESBL), and 62.7% were carbapenem resistant. Among the carbapenem-resistant isolates ( n = 37), 75.7% of metallo-beta-lactamase (MBL) producers and 70.3% carried at least one carbapenem resistance gene. The bla CTX−M gene was predominant among the ESBL-positive isolates, present in 58.8% of the P. aeruginosa isolates and 87.5% of the A. baumannii isolates, whereas 29% of both isolates harbored the bla TEM gene. Among the CR-PA isolates, 58.3% carried bla VIM−2 , 16.7% carried bla NDM−1 , and 8.33% carried bla OXA−23 . Among the CR-AB isolates, 56% harbored bla OXA−23 , 32% carried bla NDM−1 , 16% had both bla NDM−1 and bla OXA−23 , and 8% contained both bla OXA−58 and bla OXA−23 . Conclusion This study highlights a significant burden of MDR and carbapenem-resistant P. aeruginosa and A. baumannii , with the co-occurrence of carbapenem resistance genes, in a clinical setting in Nepal. Our findings suggest that active surveillance of antibiotic resistance in pathogens could inform clinicians and healthcare providers about the treatment of infections.