How microplastics contribute to antibiotic resistance

Engineers at Rice University have found that styrofoam, a form of polystyrene (a synthetic polymer), broken down into microplastics, contributes to antibiotic resistance.

According to a news release, Rice University researchers have concluded “discarded polystyrene broken down into microplastics provides a cozy home not only for microbes and chemical contaminants but also for the free-floating genetic materials that deliver to bacteria the gift of resistance.”

Publishing their findings in the Journal of Hazardous Materials, the engineers describe how the ultraviolet aging of microplastics (between 100 nanometers to five micrometers in diameter) makes them proper platforms for antibiotic-resistant genes (ARGs).

The scientists have used ultraviolet light (UV) spectrum of sunlight to age polystyrene microplastics (PS-MPs) in order to explore how aging affects antibiotic resistance genes (ARGs) transfer efficiency from various ARG vectors to recipient bacteria –– a vector, in this case, being an organism that doesn’t cause disease itself but carries pathogens from one host to another.

These antibiotic resistance genes (ARGs) are “armored by bacterial chromosomes, phages and plasmids, all biological vectors that can spread antibiotic resistance to people, lowering their ability to fight infections.”

The study led by Rice civil and environmental engineer Pedro Alvarez in collaboration with researchers in China and at the University of Houston “also showed chemicals leaching from the plastic as it ages increase the susceptibility of vectors to horizontal gene transfer, through which resistance spreads.”

Co-authors of the paper are Rice graduate student Ruonan Sun; former Rice postdoctoral researcher Pingfeng Yu, now a faculty member at Zhejiang University; associate professor Qingbin Yuan, Yuan Cheng and lecturer Wenbin Wu of Nanjing Tech University, and Jiming Bao, a professor of electrical and computer engineering at the University of Houston.

“We were surprised to discover that microplastic aging enhances horizontal ARG,” says Alvarez, the George R. Brown Professor of Civil and Environmental Engineering and director of the Rice-based Nanotechnology Enabled Water Treatment Center. “Enhanced dissemination of antibiotic resistance is an overlooked potential impact of microplastics pollution.”

According  to the researchers, the microplastics in the study, aged by UV lights of sunlight, have high surface areas that trap microbes. There are two types of microbes, according to US Centers for Disease Control and Protection (CDC): Bacteria and fungi.

“Antibiotics kill germs that cause infections. But antibiotic-resistant germs find ways to survive. Antibiotics also kill good bacteria that protect the body from infection,” the CDC notes. “Antibiotic-resistant germs can multiply. Some resistant germs can also give their resistance directly to other germs,” the CDC warns. Once antibiotic-resistant germs emerge, they can spread to new locations –– including between countries.

A significant finding of this study is that as plastics degrade – yet don’t disappear, only turn into microplastics – “they also leach depolymerization chemicals that breach the microbes’ membranes, giving ARGs an opportunity to invade.”

The scientists noted that microplastic surfaces “may serve as aggregation sites for susceptible bacteria,” increasing the speed of gene transfer by “bringing the bacteria in contact with each other and with released chemicals.”

“That synergy could enrich environmental conditions favorable to antibiotic resistance even in the absence of antibiotics, according to the study.”

THUMBNAIL IMAGE: Mucoid colonies of the pathogenic multi-drug resistant Klebsiella pneumoniae on CLED agar plate. (Getty Images/iStock)

HEADLINE IMAGE: Polystyrene breaks down into microplastics and can help microbes gain antibiotic resistance. (Journal of Hazardous Materials)