Phenotypic and genotypic characterization of carbapenemases of Pseudomonas, Acinetobacter, and Alcaligenes isolates of clinical and environmental origin

Abstract

Acinetobacter, Pseudomonas, and Alcaligenes species pose significant challenges as nosocomial pathogens, often leading to treatment failures. This study aimed to evaluate antimicrobial resistance patterns among 85 carbapenem-resistant isolates, including 40 Pseudomonas spp., 25 Acinetobacter spp., and 20 Alcaligenes faecalis from humans (8) animals/birds (42) and environment (35) sources. Assessment of antimicrobial susceptibility against 21 antibiotics using the Kirby-Bauer disc diffusion method revealed that 96.47%, 82.35%, and 61.18% of strains were resistant to imipenem, meropenem, and doripenem, respectively. Colistin was effective against Pseudomonas spp. with 77.5% susceptibility, while tigecycline showed 68% and 85% susceptibility against Acinetobacter spp. and A. faecalis, respectively. Metallo-beta-lactamase production was observed in 90.59% and 8.24% of strains by the double disk diffusion assay and Modified Hodge test, respectively. One Alcaligenes faecalis strain was pan-drug resistant. An active efflux pump was identified in 54.12% of isolates using the Ethidium Bromide cartwheel assay. Overall, 32.94% of the isolates (8 Acinetobacter spp., 14 Pseudomonas spp., and 6 Alcaligenes faecalis) possessed blaNDM genes. All Acinetobacter baumannii isolates acquired the blaOXA-51 gene. This study highlights the multiplicity and coexistence of carbapenem resistance mechanisms among these species.