Isolation of Conjugative Plasmids Carrying blaNDM Carbapenemase Gene from Environmental Bacteria in Mangonbangon River, Tacloban City, the Philippines

Abstract

Plasmids are small, self-replicating extrachromosomal DNA molecules that can move between bacteria and play a major role in the persistence and spread of antibiotic resistance, particularly in clinical settings. They often carry accessory genes conferring antibiotic resistance, metal tolerance, virulence, and metabolic capabilities, thereby playing a central role in horizontal gene transfer and the spread of these traits within environmental bacterial communities. In the Philippines, documented cases of plasmid-borne antibiotic resistance remain limited despite serious concerns over antibiotic misuse and overuse, inadequate wastewater treatment, and poor environmental management practices. This study aimed to identify carbapenem-resistant bacteria in the Mangonbangon River, Tacloban City, the Philippines, and to assess, using exogenous plasmid capture, whether carbapenem resistance genes harbored by riverine bacterial communities are carried on conjugative plasmids and transferable to a Metapseudomonas resinovorans CA10dm4RGFP recipient. The carbapenem-resistant isolates were molecularly identified as Stenotrophomonas sp., Stutzerimonas stutzeri, and Klebsiella pneumoniae. Conjugation assays using the river sample as a mixed donor community and M. resinovorans CA10dm4RGFP as the recipient yielded M. resinovorans transconjugants, indicating acquisition of plasmid-borne carbapenem resistance. PCR amplification and gel electrophoresis confirmed the presence of putative blaNDM gene amplicons in transconjugants, suggesting the transfer of a plasmid-encoded carbapenemase commonly associated with multidrug-resistant and extensively drug-resistant bacteria. This finding highlights urban river systems as active reservoirs and dissemination pathways for clinically important antimicrobial resistance (AMR) genes. Through exogenous plasmid capture, this study demonstrates the presence of transferable conjugative plasmids associated with the environmental spread of AMR.