When we think about our municipal wastewater treatment plants, we usually do not imagine them as helping hospitals to save lives. However, because antibiotic resistance is such a growing threat to the effective treatment of bacterial infections, these water-detoxification facilities can actually play a role in reducing such resistance.
Antibiotic-resistant bacteria (ARBs) increase the risk of complications while patients recover from routine surgeries and other hospital procedures. Overuse of antibiotics in medicine and agriculture, as well as antibiotic pollution contaminating the environment, exacerbate the proliferation of antibiotic resistance.
Antibiotic resistance can spread between humans and animals and across geographical borders. Therefore, effectively tackling the problem will require a “One Health” approach. As the World Health Organization describes it, this means taking into account the needs of humans, animals, and the environment in finding solutions that work for all.
Wastewater is a notorious spreader of bacteria. That is why wastewater treatment plants are crucial to cleansing ARBs from our wastewater and for removing the antibiotic residues that wastewater contains. Once treated wastewater is released back into the environment, it must be safe.
To this end, investigating the potential spread of ARBs and antibiotic resistance genes (ARGs) in wastewater treatment plants is critical.
Research conducted at the University of California, Los Angeles, has opened the door to understanding the fate of ARGs in our wastewater. Michael Stenstrom, the investigation’s lead researcher and wastewater treatment expert, notes, “Treatment plants are essentially connected to almost all the things in our daily lives. And so, we want to make sure that we’re not making antibiotic-resistant bacteria or releasing antibiotic resistance genes in our treatment plants.”
Dr. Stenstrom’s preliminary data indicates that wastewater treatment may in fact be beneficial for removing ARGs from circulation, at least to an extent. The team looked at the concentration of three different ARGs before and after treatment. The outbound samples for all plants tested showed at least a fivefold decrease in ARGs. In particular, long solids retention time (SRT) plants, which rely on longer-lived bacteria trained to break down toxins in wastewater, showed the greatest reduction rates. This is good news, since long SRT plants are highly effective at removing noxious agents from wastewater.
This is important and promising preliminary data that shows that water treatment plants can decrease ARGs. However, this is just the beginning of the possible research. More investigation is needed to understand what prevents the bacteria used in treatment plants from acquiring antibiotic resistance and if and how these plants can become more efficient in stripping ARGs and ARBs from the water supply.
Another avenue of future research is the possible effects of horizontal gene transfer (HGT) on the spread of ARGs in wastewater treatment. HGT is the ability of bacteria to transmit genetic material from one organism to another. This can result in antibiotic resistance being transmitted from one bacterium to another. Thus, it must be asked: How much HGT occurs in wastewater treatment plants?
Bacteria have a range of different mobile genetic elements (MGEs), all of which have differing abilities to spread in various environments. Some MGEs can move around within a genome, while others can be transferred from one organism to another. The question remains: Can some MGEs spread ARGs more efficiently than others in water treatment plants?
The further investigation of other ARGs and any association with MGEs may give us a deeper understanding of the role that these treatment plants can provide in pushing back against the rising tide of antibiotic resistance. Understanding the mechanisms at play is the first crucial step. Once research has uncovered how bacteria and antibiotics work in waste treatment, the door opens to tackle any vulnerabilities. We will then be able to consider using the techniques of synthetic biology to remove some of the more problematic ARGs and MGEs from the bacteria in these plants, as needed.
Advances in CRISPR-Cas gene targeting is one method to explore. Another frontier of research—one that I am currently investigating at University College London—is the construction of anti-ARG gene cassettes (pieces of genetic material transferred into bacteria) that would target and destroy ARGs.
Water treatment plants are ideal locations to test these methods of combating ARGs. The bacteria used for detoxification can be armed with anti-ARG cassettes that could both stop them from becoming reservoirs of resistance and even spread anti-resistance.
Nevertheless, as Dr. Stenstrom also advises in his research, these encouraging possibilities for future progress should not be seen as an excuse for continuing the inappropriate use of antibiotics in daily life.
*Peter Mullany is a professor of molecular microbiology at University College London.