A Review on Occurrence and Spread of Antibiotic Resistance in Wastewaters and in Wastewater Treatment Plants: Mechanisms and Perspectives

Abstract

This paper reviews current knowledge on sources, spread and removal mechanisms of antibiotic resistance genes (ARGs) in microbial communities of wastewaters, treatment plants and downstream recipients. Antibiotic is the most important tool to cure bacterial infections in humans and animals. The over- and misuse of antibiotics have played a major role in the development, spread, and prevalence of antibiotic resistance (AR) in the microbiomes of humans and animals, and microbial ecosystems worldwide. AR can be transferred and spread amongst bacteria via intra- and interspecies horizontal gene transfer (HGT). Wastewater treatment plants (WWTPs) receive wastewater containing an enormous variety of pollutants, including antibiotics, and chemicals from different sources. They contain large and diverse communities of microorganisms and provide a favorable environment for the spread and reproduction of AR. Existing WWTPs are not designed to remove micropollutants, antibiotic resistant bacteria (ARB) and ARGs, which therefore remain present in the effluent. Studies have shown that raw and treated wastewaters carry a higher amount of ARB in comparison to surface water, and such reports have led to further studies on more advanced treatment processes. This review summarizes what is known about AR removal efficiencies of different wastewater treatment methods, and it shows the variations among different methods. Results vary, but the trend is that conventional activated sludge treatment, with aerobic and/or anaerobic reactors alone or in series, followed by advanced post treatment methods like UV, ozonation, and oxidation removes considerably more ARGs and ARB than activated sludge treatment alone. In addition to AR levels in treated wastewater, it examines AR levels in biosolids, settled by-product from wastewater treatment, and discusses AR removal efficiency of different biosolids treatment procedures. Finally, it puts forward key-points and suggestions for dealing with and preventing further increase of AR in WWTPs and other aquatic environments, together with a discussion on the use of mathematical models to quantify and simulate the spread of ARGs in WWTPs. Mathematical models already play a role in the analysis and development of WWTPs, but they do not consider AR and challenges remain before models can be used to reliably study the dynamics and reduction of AR in such systems.

Sustainability of the rice-crayfish co-culture aquaculture model: microbiome profiles based on multi-kingdom analyses

“…When ARGs are transmitted into human-associated pathogens, they may pose a great environmental risk [ 22 ]. Many ARGs and other potentially harmful functional genes are spread through the environment by horizontal gene transfer (HGT) [ 23 – 25 ]. However, the current knowledge on HGT events in aquaculture models, especially those involving multi-kingdom microbes and ARGs, is limited.…”

Global distribution and diversity of prevalent sewage water plasmidomes

“…Finding replication and mobility proteins was expected as they form the backbone of plasmids, however finding several TA systems was not expected. TA systems can be thought of as selfish genetic elements, securing the stability of the plasmid carrying it through post-segregation killing 78 . It could be speculated that the relative abundance of TA systems correlates to the small size distribution of our plasmids.…”

“…It was recently indicated that methicillin resistance emerged in Staphylococcus aureus in hedgehogs as an adaptation to beta-lactam-producing dermatophyte 79 highlights the coevolution among microbes in natural habitats as important sources of AMR emergence. A high percentage of antibiotics are not fully metabolized in humans, and macrolides have been detected in wastewater 80,81 , though wastewater treatment plants lower their abundance 81,82 .…”

Antimicrobial Resistance in New Zealand—A One Health Perspective

“…Whichever treatment is used, the process is not targeted at emerging compounds (pharmaceuticals, personal care products), bacteria or their genes but aims to remove organic components, nutrients (P, N) and suspended solids. Differences in treatment plant design and operation influence the fate of ARB and ARGs in wastewater; conventional activated sludge treatment combined with advanced treatment methods—such as UV or ozonation—show improved removal of ARB and ARGs compared to activated sludge alone [ 137 , 140 , 148 ]. A recent review by Pai et al [ 149 ] estimates the removal of ARGs to be 0.1–0.6 log units with primary treatment, 1–2 log units with secondary treatment and 0–6 log units with advanced treatment methods.…”

“…Some antimicrobials, such as sulphonamides, fluoroquinolones, erythromycin and tetracycline are preferentially removed into the sludge, either by physical adsorption or enhanced adsorption through addition of flocculants [ 167 , 168 , 169 , 170 ]. The fate of ARB and ARGs through wastewater systems, including sludge, has been extensively studied, with the focus often on a small number of resistance genes or specific bacterial species [ 137 , 148 ]. Results are usually very dependent on the system studied and cannot easily be extrapolated to other WWTP and AMR determinants.…”