Water chlorination is essential for controlling harmful microbes in drinking water; however, the antimicrobial effects of chlorine-based disinfectants present in tap water may influence early-life gut microbial ecology. To investigate the functional and compositional impact of chlorinated drinking water on the gut microbiome of infants. The waTer qUality and Microbiome Study (TUMS) was an Australian-based double-blinded, randomised controlled trial. Six-month-old infants (n = 197) received either de-chlorinated drinking water via benchtop filtration (treatment, n = 99), or regular chlorinated water (control, n = 98) for twelve months. Tap water and stool samples were collected at baseline and at end of intervention. Metagenomic sequencing was used for faecal microbiome analysis. Primary outcomes were differences in gut microbiota between groups, secondary outcomes included incidence of allergic sensitization and respiratory conditions. At baseline, 170 stool samples (83 control, 87 intervention) were collected, with 130 samples obtained at the end of the intervention (65 control, 65 intervention). Overall community structure was similar between groups after the intervention, including beta diversity (0.56% variance explained; p = 0.84), richness (−4.25, 95% CI; −14.85 to 6.35, p = 0.43) or Shannon Index (−0.14, 95% CI; −0.32 to 0.04, p = 0.12). The chlorinated water group showed enrichment of antibiotic resistance MetaCyc groups and pathways (adjusted p < 0.05). Stratified analysis suggested this effect was potentiated by clinical antibiotic use. Chlorinated drinking water may enhance resistance functions in the infant gut microbiome. While remaining vital for public health, future studies should explore whether adjusting the timing or method of drinking water disinfectants into the infant diet can reduce selective pressures. ACTRN12619000458134; https://www.anzctr.org.au Parkin et al., using metagenomic sequencing, this double-blinded RCT compared gut microbiomes of infants given dechlorinated or chlorinated drinking water for 12 months. Overall composition was similar, but chlorinated water was linked to enriched antibiotic-resistance functions, especially with antibiotic use, suggesting early-life selective pressures. Chlorine is widely used to make drinking water safe, but its effects on the infant gut microbiome are not well understood. In this study, we carried out a clinical trial in which infants were given either standard chlorinated water or filtered water with chlorine removed from six to eighteen months of age. We analysed their gut microbiomes using stool samples. Overall, the diversity and overall structure of gut microbes were similar between the two groups. However, infants who drank chlorinated water showed higher levels of genes linked to antibiotic resistance. These findings suggest that while chlorination remains essential for safe water, it may influence microbial functions in early life, which could have implications for long-term health.
Parkin et al. (Wed,) studied this question.