Graphene helps wrap up treatment of antibiotic resistance

A shield of graphene helps particles destroy antibiotic-resistant bacteria and free-floating antibiotic-resistance genes in wastewater treatment plants. Think of the new strategy, developed by researchers at Rice University, as ‘wrap, trap and zap’.

The labs of Rice environmental scientist Pedro Alvarez and Yalei Zhang, a professor of environmental engineering at Tongji University in Shanghai, China, report their new strategy, which utilizes microspheres wrapped in graphene oxide, in a paper in Water Research.

Alvarez and his partners in 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 (ARGs) when they are killed as the effluent is disinfected," Alvarez said. "These ARGs are then discharged and may transform indigenous bacteria in the receiving environment, which become resistome reservoirs.

"Our innovation would minimize the discharge of extracellular ARGs, and thus mitigate dissemination of antibiotic resistance from wastewater treatment plants."

The Rice lab showed that its spheres – cores of bismuth, oxygen and carbon wrapped in nitrogen-doped graphene oxide – inactivated multidrug-resistant Escherichia 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 spheres themselves are photocatalysts that produce ROS when exposed to light. Lab tests showed that wrapping the spheres in graphene oxide minimized the ability of ROS scavengers to curtail the ability of ROS to disinfect the solution.

The researchers said 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.

"Wrapping improved bacterial affinity for the microspheres through enhanced hydrophobic interaction between the bacterial surface and the shell," said co-lead author 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 added. Tests showed that 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.

This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.