by Ashleen Knutsen
Worldwide, one in four people don’t have access to safe drinking water, particularly those living in low-income countries. Children in those regions often suffer from diarrhea and, as a result, are commonly treated with antibiotics. This has a direct impact on their long-term health.
To inactivate many of the harmful pathogens present, drinking water can be treated with chlorine; this intervention has been found to reduce the number of cases of diarrhea and antibiotic usage. However, scientists have yet to determine if water chlorination has any negative effects on the bacteria inside our digestive system.
To investigate this possibility, a team of researchers led by Amy Pickering, UC Berkeley assistant professor of civil and environmental engineering, examined the gut microbiome of children living in Dhaka, Bangladesh, one year after chlorination devices were installed in shared taps across their community. The results of the study, published in Nature Microbiology on April 14, showed that chlorination had no substantial effects on the development of the children’s gut microbiome, supporting its use as a safe treatment for drinking water globally.
“There’s always a lot of concern about having a chemical in drinking water,” said Pickering, the Blum Center Distinguished Chair in Global Poverty and Practice. “Being able to have this data showing we don’t see a big impact on the gut microbiome from chlorinated drinking water is really helpful.”
The gut microbiome is the collection of microorganisms, such as bacteria, living in the digestive system — most of which are important to overall health. Scientists have found that the gut microbiome plays a large role in metabolism, allergy development, weight gain, disease susceptibility and mental health.
However, both diarrheal pathogens and antibiotics harm its development, which occurs from birth to the age of three. In addition, overuse of antibiotics can lead to antibiotic-resistant pathogens, which is a major public health issue as well as one of the leading causes of death worldwide.
The researchers’ study cataloged both bacteria species and resistance genes present in the gut microbiomes of 130 Bangladeshi children and then compared results between those who drank chlorinated water and those who did not. The water chlorination devices were installed by the International Center for Diarrheal Diseases Research, Bangladesh, as part of a larger study by some of the authors, including Pickering, which examined the reduction in diarrhea and antibiotic use.
In this new study, the researchers found that children drinking chlorinated water had a significantly higher abundance of certain bacteria, with some populations more than twice as abundant as compared to the non-treated group. These included several bacteria linked to improved gut health. These differences, while minor, could be related to the 23% reduction in diarrhea and 7% reduction in antibiotic use found in the larger study.
There were also several antibiotic resistance genes that were found to be more abundant in children drinking chlorinated water. However, results of the bacteria analysis found that these genes were most likely a result of an increase in the presence of harmless strains of E. coli commonly found in mammals, which frequently harbor antibiotic resistance genes.
Overall, the researchers found that chlorination did not reduce the richness or diversity of bacteria species and had no negative impact on the children’s gut microbiome, supporting the use of chlorine in drinking water.
“We think that chlorination could play an important role in moving the world toward higher access to high-quality water supplies. And it’s very reassuring to have these results showing that we don’t see big negative impacts on children’s developing gut microbiomes when they’re receiving chlorinated water,” said Pickering.
This study also demonstrated the importance of examining gut microbiomes from around the world, as they develop based on diet, social networks and exposures to pathogens and the environment, which vary globally. Scientists’ current understanding of the gut microbiome comes from where it has been readily studied, which is often in high-income countries that can afford the expensive testing equipment.
“This study contributes new knowledge about what gut microbiomes and healthy gut microbiomes might look like in children in a completely different setting,” said Maya Nadimpalli, first author of the study, research assistant professor at Tufts University and member of the Stuart B. Levy Center for Integrated Management of Antimicrobial Resistance.
The researchers found that a substantial portion of the bacteria in the children’s digestive system could not be classified and may never before been cultured because they aren’t typically found in areas of the world where microbiome research is more common.
“There’s an ongoing bias in how we define basic human health, and I think studies like this are super important in expanding that definition,” said Nadimpalli. “We don’t have a very comprehensive understanding of how the microbiome differs globally between children. And that has consequences when you start trying to develop standards of what is healthy.”
Other co-authors of the study include researchers at the Ramón y Cajal Health Research Institute (IRYCIS) and the Network Research Center for Infectious Diseases (CIBERINFEC) in Spain, the Swiss Federal Institute of Aquatic Science and Technology, the Broad Institute, Stanford University, the University of North Carolina at Chapel Hill, Washington State University, the Swiss Tropical and Public Health Institute, and the University of Basel in Switzerland.