Microplastic Categories Distinctively Impact Wastewater Bacterial Taxonomic Composition and Antimicrobial Resistance Genes

Wastewater treatment plants (WWTPs) may serve as hotspots for pathogens and promote antimicrobial resistance (AMR). Plastic debris in wastewater could further contribute to AMR dissemination. The aim of this study was to investigate the impact of various microplastic types on bacterial communities and AMR gene abundance in wastewater that were obtained from two WWTPs, one in Troms & oslash;, Norway, and the other one in Potchefstroom, South Africa. The microcosm experiments were designed as follows: Five manufactured microplastic pellet types were used for testing, and two rock aggregate types were used as controls. In addition, each material type was subjected to artificial aging treatments using either ultra-violet light or hydrogen peroxide. Each material was incubated in flasks containing inlet/outlet wastewater obtained from these two WWTPs. Nucleic acids were extracted after a one-week incubation period. The detection of the blaFOX and blaMOX genes was performed using quantitative PCR. Extracted DNA was sequenced using a MinION device. Non-metric multi-dimensional scaling plot on full-length 16S sequencing data at the species level showed that samples were clustered into distinct material groups, which were in line with the ANOSIM test. The Indicator Species Analysis showed a strong association between many Acinetobacter species with the plastic group than the rock group. Aging treatment using hydrogen peroxide showed some effects on microbial composition in the outlet wastewater. The abundance of blaFOX and blaMOX genes in the Norwegian wastewater outlet were generally lower compared to those in the inlet, though the results were contrary in South African wastewater samples. The relative abundance of AMR genes seemed to be increased on several plastic types (PET, PE, and PLA) but decreased on PVC-A. WWTP treatments in this study did not effectively reduce the abundance of AMR genes. An in-depth understanding the role of specific microplastic type on bacterial communities and AMR profiles is, therefore, needed to combat AMR threat.