P096

1:Molecular Microbiology & Microbiome Group, CNC - Center for Neurosciences and Cell Biology and CIBB - Centre for Innovative Biomedicine and Biotechnology, University of Coimbra; 2:PDBEB - Ph.D. Programme in Biomedicine and Experimental Biology, Institute for Interdisciplinary Research, University of Coimbra; 3:ISPUP - Instituto de Saúde Pública da Universidade do Porto, and ICBAS - Instituto de Ciências Biomédicas Abel Salazar, University of Porto; 4:CDP Gaia and CHVNGE - Centro Hospitalar de Vila Nova de Gaia/Espinho, Unidade Local de Saúde de Gaia e Espinho, Vila Nova de Gaia; 5:Department of Life Sciences, University of Coimbra; 6:INSA – Instituto de Saúde Pública Doutor Ricardo Jorge, INSA Porto

Drinking water as a route for nontuberculous mycobacteria (NTM) infections is an emerging concern. Chlorine‐based disinfection selects chlorine‐resistant microorganisms, including opportunistic NTM, still unregulated by water‐quality directives. In plumbing, NTM persist as biofilms on pipes, taps, and showerheads, niches for accumulation and aerosol/ingestion‐mediated dissemination. The absence of routine point‐of‐use monitoring increases the risk that these resistant populations will colonize water fittings and reach susceptible individuals.

We collected running‐water and biofilm samples from taps and showerheads in 46 homes of NTM‐infected patients and 9 control households across Portugal’s North and Centre regions. Clinical isolates were dominated by M. avium (34.8%) and M. intracellulare (32.6%) with other species occurring at lower frequencies. From environmental samples, we recovered 340 isolates of 21 NTM species, mainly M. phocaicum/M. mucogenicum, M. chelonae, M. abscessus, M. stephanolepidis, M. gordonae. High‐throughput sequencing of biofilm communities partially corroborated the findings, with M. mucogenicum and M. gordonae dominating at taps and showerheads, and M. avium sequences detected sporadically.

Chlorine‐selected microbiota surviving stomach passage may interact with resident microbiota. Prolonged antibiotic therapies deplete diversity and disrupt balance, possibly compromising mucosal immunity and increasing reinfection risk. Fecal analysis of NTM patients showed loss of alpha‐diversity and shifts in immune‐regulating taxa. By linking chlorine‐driven selection in drinking water, domestic microbiota assembly, and gut resilience, our study highlights the need to revise water‐safety protocols. Adding monitoring and alternative disinfection could curb resistant biofilms, reduce exposure, and protect gut‐microbiome integrity, lowering NTM burden in vulnerable populations.

Funding: PTDC/BIA-MIC/0122/2021, 2022.06809.PTDC, UIDB/04539/2020, UIDP/04539/2020, LA/P/0058/2020, SFRH/BD/145135/2019, DL57/2016-SFRH/BPD/108299/2015.