Shedding light on antibiotic resistance

Antibiotics are simultaneously one of the greatest public health breakthroughs of the 20th century and at the heart of one of the largest public health threats in the 21st century: antibiotic resistance. A growing human population has led to greater use of antibiotics for people and in agriculture, and because antibiotics are not completely metabolized, they end up in municipal wastewater. Because most current wastewater treatment facilities cannot fully remove antibiotics, treated water and other products of the treatment process end up in the environment, creating a near ideal setting for the growth of antibiotic-resistant bacteria and transfer of antibiotic resistance genes to other organisms.

Significant research has been conducted on the use of ultraviolet (UV) light to inactivate antibiotic resistance genes. UV can damage the genetic information in these genes; however, the dose of UV needed to do so may be impractical. Thus, UV treatment is combined with various oxidation methods. A new study led by Virender Sharma, PhD, professor in the Department of Environmental and Occupational Health at the Texas A&M School of Public Health, published in the journal Frontiers of Environmental Science & Engineering, examined the effectiveness of different methods combining UV and oxidation techniques at eliminating antibiotic resistance genes in wastewater.

Sharma and colleagues reviewed recent studies on the use of UV and oxidation techniques and analyzed the results of those studies to summarize the effectiveness of different combinations. They looked at combinations of UV with chlorination—which is a commonly used disinfection method in municipal wastewater—hydrogen peroxide, peroxymonosulfate and various photocatalysis such as titanium dioxide.

Studies combining UV and chlorination examined effects on several antibiotic resistance genes using both chlorination and UV treatment alone as well as UV treatment followed by chlorination and found that using the two methods in sequence was more effective than either method alone at eliminating antibiotic resistance genes in wastewater. Other studies looked at similar methods using UV and hydrogen peroxide and UV and peroxymonosulfate treatment, which produce radicals that rapidly degrade organic materials in wastewater. They found that UV treatments alone were more effective at eliminating antibiotic resistance genes than UV combined with peroxymonosulfate or hydrogen peroxide, but that both peroxymonosulfate and hydrogen peroxide were highly effective at removing antibiotic contaminants. One possibility the researchers noted is that substances produced by chemical reactions involving peroxymonosulfate or hydrogen peroxide absorb UV, limiting its ability to degrade antibiotic resistance genes.

Sharma and colleagues also examined the use of photocatalysts like titanium dioxide that produce reactive oxygen species under UV. Such reactive oxygen species could inactivate both antibiotic-resistant bacteria and antibiotic resistance genes. One study found that such treatments must be conducted for long periods. Additionally, photocatalyst treatments had varying effects depending on substances present in wastewater. The notion is that certain organic and inorganic substances in wastewater could react with reactive oxygen species, reducing the processes efficiency.

The studies Sharma and his colleagues analyzed point to different wastewater treatment methods involving UV having varying degrees of effectiveness at removing antibiotic resistance genes. These findings point to the need for additional studies investigating the exact mechanisms by which different treatment methods inactivate antibiotic resistance genes and how different types of antibiotics affect the process.

“With a better understanding of how different methods work, researchers will be better able to develop treatment techniques that can effectively eliminate antibiotic resistance genes and antibiotic-resistant bacteria in wastewater, thus limiting a major risk factor for a growing public health threat,” Sharma said.