Growth and prevalence of antibiotic-resistant bacteria in microplastic biofilm from wastewater treatment plant effluents

It is accepted that Microplastic (MP) biofilms accumulates antibiotic-resistant bacteria (ARB) and antibiotic-resistant
genes (ARGs) in water. ARB/ARGs and MPs are emerging pollutants of concern due to various associated health
risks. The objective of this study was to 1) investigate the ARB community in a pilot-scale wastewater treatment
plant (WWTP) effluent, 2) to study and visualize the ARB/ARGs in MP biofilm grown in WWTP effluent and tap
water, and 3) to analyze microplastic adherent ARB/ARGs in the biofilm and planktonic ARB/ARGs in the filtrate
under controlled conditions. Results indicated the dominance of Pseudomonas, Aeromonas, and Bacillus among isolated
ARB inWWTP effluent. Representative resistance strains were incubated in 300mLwater containing commercial polystyrene
beads of 300550 μm diameter (MP) in a series of batch experiments. Microbiological, molecular, and microscopic
analyses were performed by enumeration, 16srRNA, real-time polymerase chain reaction (qPCR), and Field
Emission-Scanning Electron Microscopy (FEG-SEM) techniques. The analyzed viable ARB indicated an increasing
trend in MP biofilms between days 3 and 5. It further decreased on days 7 and 9. The prevalence of ARB in the filtrate
and MP biofilm varied as a function of time and TOC level, while no significant impacts were observed for minor
temperature variation, low antibiotic pressure, and increased MP mass with few exceptions. Relative abundance of
ARGs (vanA, sul1) and integron integrase gene (intl1) inMP biofilm were significantly different across different TOC
levels, time, and antibiotic pressure. ARGs and intl1 were detected in the MP biofilm in tap water andWWTP effluent
on day 30.