OR06

1:Research Center Borstel; 2:Goethe University Frankfurt; 3:San Raffael Scientific Institute

Non-tuberculous mycobacteria (NTM) are environmental bacteria increasingly recognized as causes of severe disease, particularly in vulnerable individuals. Yet, key reservoirs and routes of human exposure remain insufficiently characterized. In this study, we investigated the presence and genetic diversity of NTM in 102 indoor water samples collected from private households and a hospital in Frankfurt am Main, Germany. Isolates were characterized via whole genome sequencing, drug susceptibility testing, and core genome multi-locus sequence typing (cgMLST) to assess potential links with nearly 3,000 global clinical and environmental NTM isolates. NTM were isolated from 19.5% of households and 14.7% of samples, with a higher recovery from shower water (29.3%) compared to tap water (9.2%). Eight different species were identified, including one putative novel species. Rapid and slow-growing NTM were dominated by M. chelonae and M. chimaera, respectively. None of the isolates were resistant to macrolides or aminoglycosides. Several isolates from household water showed high genetic similarity to clinical strains from Germany and abroad. Strikingly, we detected a M. abscessus strain belonging to the dominant circulating clone DCC3 — which is one of the most frequently isolated clones from NTM patients globally — in a shower water sample. Additionally, we describe for the first time dominant circulating clones of M. chelonae. These findings reinforce the relevance of indoor water systems as reservoirs for clinically important NTM and emphasize the need for targeted One Health interventions to minimize exposure, particularly among at-risk populations.