A reliable way to get rid of antibiotic-resistant bacteria in water treatment plants is a combination of solar irradiation and bacteriophage treatment.

Wastewater generated after water use by industrial and municipal facilities requires thorough treatment, particularly to remove hazardous microorganisms. Wastewater is known to be a true "incubator" for antibiotic-resistant bacteria. It typically contains large quantities of antibiotics from livestock farms, creating conditions conducive to the selection of resistant bacterial strains. It also contains numerous bacteria that readily transmit antibiotic resistance genes to one another. These bacteria are often able to resist not only antibiotics but also various traditional water treatment methods.

The problem of purifying water from antibiotic-resistant bacteria is extremely pressing in regions with a shortage of fresh water, where it is essential for all kinds of economic purposes. For example, last year in Saudi Arabia, a simple and inexpensive method of disinfecting water using solar irradiation was proposed*. Ultraviolet light kills bacteria by damaging their DNA and also releases active oxygen from organic matter in the water, which also has a bactericidal effect. When the method was tested on E. coli, which is resistant to the vast majority of antibiotics, including the latest ones, it was found that three times as long of a period of solar ultraviolet irradiation was required to inactivate it. This is because certain genes are activated in response to irradiation, which help bacteria restore components damaged by the radiation. However, it was also discovered that the bacteria's defense system against viruses—bacteriophages—is simultaneously impaired.

In a new study**, scientists tested the effectiveness of a new water disinfection method using solar radiation and bacteriophages. They isolated bacteriophage strains specific to antibiotic-resistant E. coli and relatively resistant to ultraviolet radiation.

By combining bacteriophages with solar ultraviolet light, it was possible to destroy resistant E. coli twice as quickly as without the use of phages.

The study's authors point out that, thanks to the high specificity of bacteriophages, there is no need to worry that this purification method will disrupt the ecosystems into which this water enters.

* Al-Jassim N, Mantilla-Calderon D, Wang T, and Hong PY. Inactivation and Gene Expression of a Virulent Wastewater Escherichia coli Strain and the Nonvirulent Commensal Escherichia coli DSM1103 Strain upon Solar Irradiation // Environ. Sci. Technol., 2017, 51(7): 3649-3659. DOI: 10.1021/acs.est.6b05377

** Al-Jassim N, Mantilla-Calderon D, Scarascia G, and Hong PY. Bacteriophages To Sensitize a Pathogenic New Delhi Metallo β-Lactamase-Positive Escherichia coli to Solar Disinfection // Environ. Sci. Technol., 2018, 52(24): 14331-14341. DOI: 10.1021/acs.est.8b04501