Reservoirs of antibiotic resistance and pathogens in bacterial communities of anthropogenically - driven environments

The increase of antibiotic resistance against antibiotics (AB) is an alarming phenomenon threatening the human well being and heading back to the pre-antibiotic era where many infectious diseases may become again untreatable with antibiotics. There is a strong correlation between AB use and occurrence of resistances which suggests anthropogenically-driven environments as reservoirs of antibiotic resistant bacteria (ARB). Among anthropogenically - driven environments, wastewater treatment plants (WWTPs), have been linked with the increased incidence of pathogens and ARB in freshwater ecosystems. Principal goal of the study was to evaluate the role of WWTPs as environmental reservoirs for antibiotic resistance and pathogenic bacteria. In this thesis, classical and molecular microbiology methods were applied to analyse resistance levels of bacterial communities from wastewater and wastewater-polluted environments at different geographical locations of developed (German and Switzerland) and developing (Nigeria) countries. Additionally, a novel approach which makes use of a combination of quantitative genomics, Next Generation Sequencing and drug-related health data was applied to quantitatively detect antibiotic resistance genes (ARG) in wastewater and assess their seasonal dynamics. The relative abundance of ARG was not reduced by the WWTPs in the treated effluent. Effluents were responsible for significantly high levels of ARB and ARG in the receiving environment because capable of introducing and/or selecting ARB carrying ARG on genetic mobile elements. The ARG levels differed between seasons independently from the water sanitation. High ARG levels were displayed in autumn and winter in coincidence with the higher uptake of antibiotics by the outpatients of the municipality.Contrary to the ARG, the abundance of bacteria was reduced by WWTPs processes in the effluent of developed countries. The WWTPs were also responsible for the changes of the microbial community from the wastewater to the effluent. Contrary to developed countries, the poor treatment of wastewater in Nigeria facilitated the spread of multi-drug resistant pathogens in the freshwater ecosystem. These bacteria were also carriers of clinically relevant ARG contributing to the accumulation of multiresistant pathogens in the environment. All in all, this thesis shows that well established WWTP technologies are not capable to prevent or reduce the abundance of ARG in the freshwater ecosystem and poorly treated wastewater enriches the environmental reservoirs of ARG. Antibiotic resistance can spread across taxonomically distant bacteria and therefore explain the strong dispersal of ARG in wastewater effluents. These results show that antibiotic resistances are also ubiquitous in the freshwater environment and that anthropogenically - driven environments determine the incidence of antibiotic resistance. As for the clinic, tackling the problem of antibiotic resistance in the environment is fundamental. Without any action, the environmental reservoirs of resistance will increase and therapeutic failure in the clinic will irreversibly compromise the biggest progress in medicine of the 20th century.