Persistence and dissemination of the multiple-antibiotic-resistance plasmid pB10 in the microbial communities of wastewater sludge microcosms

Plasmid-mediated dissemination of antibiotic resistance genes is widely recognized to take place in many environmental compartments but remains difficult to study in a global perspective because of the complexity of the environmental matrices considered and the lack of exhaustive tools. In this report, we used a molecular approach based on quantitative PCR to monitor the fate of the antibiotic resistance plasmid pB10 and its donor host in microbial communities collected from various wastewater treatment plant (WWTP) sludges and maintained in microcosms under different conditions. In aerated activated sludge microcosms, pB10 did not persist because of an apparent loss of the donor bacteria. The persistence of the donor bacteria noticeably increased in non-aerated activated sludge microcosms or after amending antibiotics (sulfamethoxazole or amoxicillin) at sub-inhibitory concentrations, but the persistence of the donor bacteria did not stimulate the dissemination of pB10. The dissemination of the plasmid appeared as an increasing plasmid to donor ratio in microcosm setups with microbial communities collected in anaerobic digesters or the spatially organized communities from fixed biofilm reactors. As a whole, the data collected suggest that some WWTP processes, more than others, may sustain microbial communities that efficiently support the dissemination of the multiple-antibiotic-resistance plasmid pB10.