Species Diversity of Nontuberculous Mycobacteria in Dental Unit Waterlines: Implications for Infection Control and Clinical Practice.

BACKGROUND: Dental unit waterlines (DUWLs) are prone to microbial biofilm formation and serve as reservoirs for opportunistic nontuberculous mycobacteria (NTM) that pose infection risks in dental settings. Regional data on the diversity of NTM species in DUWLs, particularly in Iran, remain limited. OBJECTIVE: This study aimed to determine the prevalence and species diversity of potentially pathogenic NTM in DUWLs from dental practices in Tabriz, Iran. METHODS: Thirty 500-mL water samples were collected from DUWLs in private and university-affiliated clinics (May-October 2024) after a 20-30 s flush. Samples were filtered, decontaminated with 0.01% cetylpyridinium chloride, cultured on Löwenstein-Jensen slants at 37°C for 8 weeks, and confirmed as acid-fast bacilli by Ziehl-Neelsen staining. Species identification was performed using partial hsp65 gene sequencing and the Nucleotide Basic Local Alignment Search Tool (BLAST) comparison with NCBI GenBank. RESULTS: NTM was isolated from 13 samples (43.33%), yielding 13 isolates. Seven isolates (53.85%) were rapidly growing mycobacteria (RGM: M. abscessus [n = 2], M. fortuitum [n = 3], M. mucogenicum [n = 2]), and six (46.15%) were slow-growing (SGM: M. gordonae [n = 4], M. kansasii [n = 1], M. simiae [n = 1]). M. gordonae was predominant (30.77%). None of the samples yielded multiple NTM species. CONCLUSION: DUWLs in Tabriz harbor diverse NTM with clinical relevance, including rapidly growing species. These findings highlight DUWLs as a potential source of opportunistic infections and emphasize the need for NTM-targeted water quality monitoring and enhanced infection control measures in dental facilities.