Wastewater treatment to fight the spread of antibiotic resistance

The need to tackle antibiotic resistance is becoming more urgent, posing threats to the health of all species, as antibiotic resistance genes (ARGs) proliferate in the wider environment. Wastewater treatment plants are a key hotspot for the spread of antimicrobial resistance, because ARGs present in waste from humans can pass through the treatment process intact and disseminate into the environment.

“Solid waste, or sludge, is a byproduct of wastewater management that is regularly discharged into the environment after wastewater is treated,” says Julie Sanchez Medina, Ph.D. student at KAUST, who is supervised by faculty member Pei-Ying Hong. “However, sludge now contains considerable numbers of ARGs, and they are free to potentially move between species in the sludge, spreading antimicrobial resistance still further.”

Now, a metagenomics study by Sanchez Medina and co-workers has demonstrated that one type of bioreactor used in some wastewater plants – anaerobic membrane bioreactors – may be better at reducing the amount of ARGs released into the environment^[1].

Membrane bioreactors use a bacterial digestion process to break down organic pollutants in wastewater. This digestion process either uses aerobic bacteria (those that thrive with oxygen) or anaerobic bacteria (without oxygen). The wastewater is then filtered through a membrane to separate out the contaminants, resulting in clean fluid effluent and leaving behind the solid sludge.

“We wanted to examine whether there are differences in the amount of ARGs and antibiotic-resistant bacterial strains in the sludge produced by aerobic or anaerobic membrane bioreactors,” says Sanchez Medina.

The team compared two systems that were treating the same stream of wastewater, and collected sludge from each of them in two independent runs during a five-month period. They extracted DNA from the sludge, then sequenced and analyzed it with bioinformatic tools. The resulting datasets enabled the researchers to estimate the abundance of ARGs according to the sludge volume that was released by each bioreactor.

“We found that sludge from the anaerobic system had a lower abundance of ARGs. Crucially, there was also a lower potential for the horizontal transfer of genes to opportunistic pathogens in the anaerobic system compared to the aerobic one,” says Sanchez Medina.

The team also examined the diversity in the types of antibiotic resistance for each system. Aerobic sludge had a higher diversity of potentially harmful ARGs, including those that confer resistance to broad-spectrum antibiotics like quinolones and tetracycline. Anaerobic sludge had fewer mobile genetic elements and the conditions within the system were less conducive to gene transfer.

“Coupled with the other advantages of anaerobic membrane bioreactors – lower overall sludge waste and lower energy requirements – this technology may be especially useful in the fight against antimicrobial resistance,” notes Hong.

“We plan to conduct a further, long-term study of anaerobic versus aerobic systems to gain more insights into the risk of antibiotic resistance dissemination and the downstream impacts in terms of reusing treated wastewater, which is a vital consideration for an arid country such as Saudi Arabia,” concludes Sanchez Medina.

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