Impact of Microplastic Contamination on Antibiotic Resistance Gene Enrichment and Transfer in Aquatic Environments Receiving Hospital Effluents in Lagos State

Microplastics have emerged as a novel environmental AMR vector, providing hydrophobic surfaces that concentrate antibiotics, facilitate biofilm formation by resistant bacteria, and promote horizontal gene transfer of resistance determinants at rates exceeding those in surrounding water. The intersection of microplastic pollution and antimicrobial resistance in aquatic environments receiving Nigerian hospital effluents represents an entirely uncharacterized research frontier. This study investigated the role of microplastic contamination in antibiotic resistance gene enrichment and conjugation dynamics in water bodies receiving hospital effluents in Lagos State, South West Nigeria. Microplastics were collected by manta trawl and Nile Red staining from three water bodies receiving hospital effluents and three reference sites. Biofilm communities on microplastic surfaces and surrounding water were characterized by 16S rRNA sequencing and shotgun metagenomics. ARG abundance on microplastic-associated biofilms versus bulk water was compared using metagenomic data. In vitro conjugation experiments quantified plasmid transfer efficiency in biofilms formed on polystyrene microplastics versus glass surfaces. Results showed 12 to 37-fold higher ARG concentrations on microplastic-associated biofilms compared to bulk water. blaNDM, mcr-1, and rmtB methylase genes were detected exclusively on microplastic biofilms at three sites. Conjugation efficiency on polystyrene surfaces was 4.8-fold higher than on glass, confirming microplastics as horizontal gene transfer hotspots. Microplastic-enriched taxa included Acinetobacter species and Pseudomonas species carrying multiple resistance integrons. This study constitutes an original interdisciplinary contribution linking environmental microplastics science with pharmaceutical microbiology and AMR ecology in the Nigerian aquatic context. Keywords: microplastics, antibiotic resistance genes, horizontal gene transfer, hospital effluent, Lagos.