Cleansing the Water from Antibiotic Resistance Genes (ARGs)

                              

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Cleansing the Water from Antibiotic Resistance Genes (ARGs)

Wastewater treatment is a control unit that protects environmental and subsequently human health against the spread of pathogens harboring virulence or drug resistance genes. The treatment requires processes that inactivate or eliminate the potentially harmful proportion of the microbial community and their genes. Removal of drug-resistant genes has turned out to be a challenging task and yet, there seems to be no standardized approach to ensure quality and efficiency.

Advanced approaches to tackle this challenge include disinfection technologies such as membrane bioreactors, chlorination, ultraviolet radiation, ozonation ,thermophilic anaerobic digestion or engineered lytic phages (figure 1). All these technologies are trying to block microorganisms from continuing their travel from wastewater to rivers and oceans exposed to humans, animals, and plants. Some of those technologies interrupt communication routes between microorganisms so that the exchange of drug-resistant genes becomes less likely. Nevertheless, microorganisms do not easily give in. Thus, current disinfection technologies come with certain limitations. 

Figure 1 Travel routes of antibiotic resistance genes (ARGs) to humans. Different disinfection technologies implemented in Wastewater Treatment Plants (WWTP) can block this travel route and reduce the abundance of antibiotic-resistant bacteria. Adapted from: Nguyen, A. Q., et al. (2021). “Monitoring antibiotic resistance genes in wastewater treatment: Current strategies and future challenges.” Sci Total Environ 783: 146964.

Chemical treatment processes for example reduce the number of drug-resistant bacteria and the events of horizontal gene transfer, but their efficiency is kept within limits when moving from a laboratory scale to the wastewater treatment plants. In the latter scenario, researchers in Switzerland (Czekalski et al., 2016) have discussed the potential production of harmful by-products when using high doses of chlorine or ozone. They also studied the risk of selection by which highly resistant strains survive and regrow during and following treatment. 

Moreover, temperature treatment reduced the abundance of drug-resistant genes, yet this reduction could be specific only to certain genes as another research group (Zhang et al., 2015) pointed out. They found that thermophilic anaerobic digestion in sewage sludge removed over 90% of quinolone resistance genes while it simultaneously enriches chloramphenicol resistant genes.

Building on the existing techniques, Hembach and his colleagues performed experiments to compare the efficiency of ultrafiltration and ozone treatment in reducing antibiotic resistance genes. The results showed that both techniques reduce the abundance of bacteria including E. coli, A. baumannii, and Enterococci to a greater extent compared to prior conventional biological treatment.

Figure 2 Abundance of facultative pathogenic bacteria (A) and different antibiotic resistance genes (B) after conventional biological treatment followed by treatment with ozone or two ultrafiltration units (UF) of different modes, pore size, and flux. Source: Hembach, N., et al. (2019). “Dissemination prevention of antibiotic-resistant and facultative pathogenic bacteria by ultrafiltration and ozone treatment at an urban wastewater treatment plant.” Sci Rep 9(1): 12843.

Ozone is a chemical that oxidizes the organic compounds of bacteria cells and thereby weakening or killing them. On the other hand, ultrafiltration removes the bacterial cells from wastewater by choosing a membrane with a pore size that bacteria and other microorganisms cannot pass. In this experiment, treatment of wastewater with ozone alone was less sufficient in the reduction of bacterial cells compared to ultrafiltration as observed with bacterial cells that carry the CTX-M-32 gene – a ß-lactamase against cephalosporins (figure 2). Nevertheless, treatment with ozone has its strengths in reducing micro-pollutants like antibiotic drugs or biocides. For this reason, researchers of this study (Hembach et al., 2019) recommend future studies to consider combined technologies for instance ozonation followed by adsorption filtration and membrane-based ultrafiltration. 

As antibiotic resistance genes are continuing to travel along water streams, especially those of hospitals and pharmaceutical companies, innovative development and combination of existing technologies are ways to intervene and prevent the selection or regrowth of resistant bacteria.


Link to the original post: Nguyen, A. Q., et al. (2021). “Monitoring antibiotic resistance genes in wastewater treatment: Current strategies and future challenges.” Sci Total Environ 783: 146964. https://www.sciencedirect.com/science/article/pii/S0048969721020349?via%3Dihub

Other reference

Hembach, N., et al. (2019). “Dissemination prevention of antibiotic resistant and facultative pathogenic bacteria by ultrafiltration and ozone treatment at an urban wastewater treatment plant.” Sci Rep 9(1): 12843.