Test the extent to which water-based disinfectants damage antibiotic resistance genes – ScienceDaily

These bacteria can end up in our water, which is why we use disinfectants to kill them or prevent them from multiplying to treat waste and drinking water.

But so far, few researchers have investigated whether these treatments are effective at removing the genes encoding the traits that make these bacteria resistant to antibiotics. Some researchers fear that even after treatment, non-resistant bacteria can become so by recovering intact genes left behind by damaged bacteria that are resistant to antibiotics.

Although it is not clear if this is happening now, researchers want to be prepared for this scenario. A team from the University of Washington has therefore tested the effectiveness of current methods of water and wastewater disinfection on antibiotic resistance genes present in bacterial DNA. Although these methods work well to discourage bacterial growth, they have had varying success in degrading or disabling a gene representative of antibiotic resistance.

The researchers recently published their findings in the journal Environmental Science and Technology and develop a model for the appropriate treatment of any antibiotic resistance gene.

"DNA is not particularly toxic or harmful in itself, but it's important to take into account one's fate once it's in the environment because it can potentially spread undesirable traits in bacterial communities, "said corresponding author Michael Dodd, badociate professor in the civil and environmental sectors of UW. engineering department. "We have found more and more medically relevant antibiotic resistance genes in the environment.

"Recognition of the presence of these genes in the environment is not new – other groups have already provided much information about their behavior as environmental contaminants." that is unique in our work, it is that we focus on the clarification and characterization how various disinfection processes affect the fate of these genes, so that we can better understand how these different treatments affect bacteria resistant to antibiotics and their DNA in our water. "

Current water treatment plants use various methods of disinfection. Most involve exposing the water to UV light or to compounds containing chlorine or oxygen, such as chlorine alone or ozone.

To determine how these methods affect the resistance genes to bacteria and antibiotics, Dodd and his team used a model system: a harmless soil bacterium called Bacillus subtilis. The team worked with a strain of B. subtilis which overproduces a gene, called blt, that makes a protein that allows B. subtilis pump antibiotics – making the bacteria resistant to a variety of common antibiotics.

The researchers exposed the bacteria to different methods of disinfection and then monitored two things: the degree of growth of the bacteria treated when they were exposed to antibiotics and the fact that the gene inside the bacteria was damaged.

"As we expected, all the treatments we examined managed to disrupt bacterial viability," said the first author, Huan He, PhD student in civil and environmental engineering from UW. "But we have seen mixed results for DNA damage."

At typical exposures used for water treatment, three methods have shown a degradation or deactivation of the gene greater than 90%: UV light, ozone and chlorine. The team determined that these three methods are largely effective in preventing the spread of antibiotic resistance, both by disabling the bacteria and damaging the resistance gene.

However, two other disinfectants called chlorine dioxide and monochloramine have almost no damage to the gene.

"We found that these two methods degrade DNA so slowly that almost nothing happened during the time of exposure to water under typical treatment conditions," he said. Hey. "In fact, we have found that DNA from chlorine dioxide and monochloramine-treated bacteria retains the ability to transfer antibiotic resistance traits to non-resistant bacteria long after the original bacteria have been killed. "

Currently, the team knows how fast these disinfection methods affect the gene used in the study. Researchers are developing a model to estimate the speed with which a gene would be damaged.

"If we can predict the effectiveness of each disinfection method in disabling or degrading a specific gene, then we can better evaluate effective treatment strategies to break down any antibiotic resistance genes that have a problem," Dodd said. "Disinfection processes are very important tools for preventing the spread of antibiotic resistance, and we are trying to understand them better so that we can design and use them more effectively in the future."