Microplastics\nMay Not Proliferate Antibiotic Resistance\nduring Mainstream Anaerobic Treatment

Microplastics and antimicrobial resistance are pressing\nenvironmental\nchallenges requiring immediate action. Biofilms on the surface of\nmicroplastics, known as the plastisphere, may play a role in the proliferation\nof antibiotic resistance genes (ARGs). Microplastics can adsorb contaminants,\nsuch as antibiotics via hydrophilic interactions, exposing nearby\nmicroorganisms to elevated selective pressures. This study aimed to\ncompare ARG levels in distinct microbial environments found in anaerobic\nmembrane bioreactors (AnMBRs) across increasing microplastic exposure\n(i.e., 1, 2, and 5 g/L) while treating synthetic domestic wastewater\nsupplemented with 50 μg/L antibiotics (sulfamethoxazole, ampicillin,\nerythromycin, and colistin). Novel duplex-digital droplet PCR (ddPCR)\nassays were developed to quantify ARGs conferring resistance to the\nspiked antibiotics. Microbial colonization of the plastisphere was\nobserved through scanning electron microscopy. Fourier transform infrared\nspectroscopy confirmed a decreased intensity of chemical spectra over\ntime, indicating weathering of polyethylene. Across the biomass, membrane\nbiofilm, plastisphere, and effluent, a pronounced increase in the\nnumber of ARGs was not observed relative to the control AnMBR without\npolyethylene. DNA- and RNA-based amplicon sequencing showed that biomass,\nmembrane biofilm, and plastisphere microbial communities were similar\nand were largely unaffected by long-term exposure to polyethylene.\nHowever, the effluent microbial community was remarkably different\nand was significantly impacted by polyethylene addition.