Intergeneric conjugative transfer of plasmid-associated antibiotic resistance genes from environmental Aeromonas spp. to gram-negative recipient strains.

BACKGROUND: Wastewater released from hospitals acts as environmental reservoir of antibiotic-resistant genes (ARGs) harbouring bacteria and act as disseminators of antimicrobial resistance (AMR). To determine the mechanism of horizontal gene transfer (HGT) conjugation assay was performed.

MATERIALS AND RESULTS: The present study focuses on environmental plasmid mediated HGT of multidrug resistant (MDR) Aeromonas spp. recovered from hospital effluents to bacteria such as Escherichia coli and Salmonella enterica serovar Typhimurium. Broth mating conjugation assays exhibited variation in the conjugation frequency across the strains. Molecular analyses verified the transmissibility of the plasmids from the donor strains conferring clinically relevant resistance genes (tet(A), OXA-513, KPC-2, mexC and vanA) to recipient strains. The study also revealed selective plasmid mobilization, as no conjugative transfer was observed from two donor strains. The remaining donor strains demonstrated transferability, supported by the presence of genes required for conjugative transfer, mobilization and integrase activity. Plasmid curing under non-selective conditions demonstrated progressive plasmid segregation. The persistence and acquisition of ARGs post-transfer was confirmed by quantitative PCR (qPCR), with highest abundance of tet(A) gene across all transconjugants.

CONCLUSION: Conjugation assays demonstrated laboratory-based horizontal transferability of ARGs, and plasmid curing assays support the plasmid-associated nature of the detected resistance determinants. Understanding these gene transfer mechanisms offer insights crucial for developing effective surveillance and mitigation strategies.