Engineers have developed a new approach for turning ordinary water into a weapon against antibiotic-resistant bacteria, according to a study publishing September 30 in the Cell Press journal Chem Catalysis.
The research hinges on a new kind of crystal made from titanium dioxide. These crystals transform the normal oxygen molecules in water into a special molecule known as "singlet" oxygen. Singlet oxygen is nearly identical to the gas in the air you breathe, known as "triplet" oxygen, but it's much more chemically reactive—which allows these molecules to seek out and attack chunks of bacterial DNA floating in water. The researchers envision their approach could one day help cities treat water supplies, preventing antibiotic-resistant bacteria from reaching your kitchen faucet.
"Unlike conventional disinfection approaches that may require continuous addition of chemical oxidants, this system uses oxygen naturally available in the environment to disinfect water," says co-author Xinjian Shi of Henan University in China.
The study tackles a growing problem around the world; in recent decades, bacteria and other pathogens have evolved resistance to common medications like antibiotics at an alarming rate. Scientists have experimented with various approaches to killing these microbes, including bathing water in intense ultraviolet light. But those techniques have a major drawback. They eliminate bacteria but leave behind something potentially just as dangerous: their DNA.
"The persistence of this genetic material is an environmental concern because extracellular DNA can be taken up by other microorganisms, potentially leading to the spread of antibiotic resistance," says co-author Boxia Liu of North Minzu University in China.
To address those challenges, the researchers decided to target not just bacteria but their genes as well by designing specialized titanium dioxide crystals. The crystals include tiny defects, or "oxygen vacancies," a bit like the dimples on a golf ball. When the researchers shone light irradiation on these crystals, they observed that ordinary oxygen molecules interacted with those defect sites. The crystals then catalyzed a series of chemical reactions that transformed triplet oxygen into singlet oxygen—which exists in nature but is much rarer than triplet oxygen—at a fast rate.
"Catalyst defects should not simply be considered as imperfections in a material structure," says co-author Zhi Song of North Minzu University. "When properly engineered, defects can actively regulate how molecules interact with catalyst surfaces and determine the pathways through which chemical reactions proceed."
Singlet oxygen has a big appetite for picking up electrons from the environment. As a result, these oxygen gases are attracted to other molecules that are rich in electrons, including the base pairs in DNA. When singlet oxygen encounters DNA, it strips electrons away from those base pairs, a reaction known as oxidation. In the process, the base pairs get cut in two, destroying the genetic information contained in DNA.
The researchers tested this concept in a series of experiments. They added molecules related to DNA to water alongside their titanium dioxide catalysts. The catalysts completely degraded the DNA-related molecules.
The team hopes that this method could help fight antibiotic resistant genes on a large scale, but there is still a lot more work to do before these crystals show up in real water treatment facilities. Scientists, for example, will need to evaluate the safety of this technology for the environment and for people. But because the system activates oxygen in a controlled manner, it may be safer than other technologies that require constantly adding chemical oxidants to water.
