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Scientists ‘wrap, trap and zap’ superbugs in wastewater

Image credit: Mulderphoto/Dreamstime

A shield of graphene helps particles destroy antibiotic-resistant bacteria and free-floating antibiotic resistance genes in wastewater treatment plants, new research has found.

Described as “wrap, trap and zap,” the strategy was developed at Rice University in Houston, Texas by environmental scientist Pedro Alvarez and Yalei Zhang, a professor of environmental engineering at Tongji University, Shanghai, who introduced microspheres wrapped in graphene oxide as part of the research.

Alvarez and his partners at the Rice-based Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT) have worked toward quenching antibiotic-resistant 'superbugs' since first finding them in wastewater treatment plants in 2013.

“Superbugs are known to breed in wastewater treatment plants and release extracellular antibiotic resistance genes when they are killed as the effluent is disinfected,” Alvarez explained.

“These ARGs are then discharged and may transform indigenous bacteria in the receiving environment, which become resistome reservoirs,” he added. “Our innovation would minimise the discharge of extracellular ARGs, and thus mitigate dissemination of antibiotic resistance from wastewater treatment plants.”

Improved bacterial affinity and reactive oxygen species generation enhances antibacterial inactivation in wastewater by graphene oxide-wrapped nanospheres developed by scientists at Rice University and Tongji University, Shanghai. Antibiotic resistance genes (eARG) released by inactivated antibiotic resistant bacteria (ARB) in the vicinity of photocatalytic sites on the spheres facilitates their degradation.

Improved bacterial affinity and reactive oxygen species generation enhances antibacterial inactivation in wastewater by graphene oxide-wrapped nanospheres developed by the scientists. Antibiotic resistance genes (eARG) released by inactivated antibiotic resistant bacteria (ARB) in the vicinity of photocatalytic sites on the spheres facilitates their degradation.

Image credit: Alvarez Research Group/Rice University

The Rice lab showed its spheres – cores of bismuth, oxygen and carbon wrapped with nitrogen-doped graphene oxide –  inactivated multidrug-resistant Escherichia coli (E.coli) bacteria and degraded plasmid-encoded antibiotic-resistant genes in secondary wastewater effluent. The graphene-wrapped spheres kill nasties in effluent by producing three times the amount of reactive oxygen species (ROS) as compared to the spheres alone, the researchers said. 

The spheres themselves are photocatalysts that produce ROS when exposed to light. Lab tests showed that wrapping the spheres minimised the ability of ROS scavengers to curtail their ability to disinfect the solution.

The researchers added that nitrogen-doping the shells increases their ability to capture bacteria, giving the catalytic spheres more time to kill them. The enhanced particles then immediately capture and degrade the resistant genes released by the dead bacteria before they contaminate the effluent.

An electron microscope image shows E. coli bacteria trapped by wrapped microspheres developed at Rice and Tongji universities. The spheres were created to disinfect secondary effluent from wastewater treatment plants, a breeding ground for antibiotic resistant bacteria and antibiotic resistance genes.

An electron microscope image shows E. coli bacteria trapped by wrapped microspheres. The spheres were created to disinfect secondary effluent from wastewater treatment plants, a breeding ground for antibiotic resistant bacteria and antibiotic resistance genes.

Image credit: Deyi Li/Tongji University

“Wrapping improved bacterial affinity for the microspheres through enhanced hydrophobic interaction between the bacterial surface and the shell,” said Pingfeng Yu, a postdoctoral research associate at Rice’s Brown School of Engineering. “This mitigated ROS dilution and scavenging by background constituents and facilitated immediate capture and degradation of the released ARGs.”

Because the wrapped spheres are large enough to be filtered out of the disinfected effluent, they can be reused, Yu said. Tests showed the photocatalytic activity of the spheres was relatively stable, with no significant decrease in activity after 10 cycles. That was significantly better than the cycle lifetime of the same spheres minus the wrap, Yu disclosed. 

At the start of July, scientists at the UK Centre for Ecology & Hydrology (UKCEH) announced the development of a standardised system to detect coronavirus in wastewater as a way to monitor future outbreaks in the UK.

Back in May, scientists at Water Research Foundation (WRF) said they were looking at how wastewater analysis can be used to find Covid-19 hotspots among the population.

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