PubMed2026
The genus Mycobacterium, including Mycobacterium tuberculosis and over 200 nontuberculous mycobacteria (NTM), shows wide variability in clinical outcomes and drug susceptibility. Although culture-based identification remains the gold standard, slow mycobacterial growth delays diagnosis and treatment. In this study, we evaluated a novel culture-free method for subspecies-level identification directly from sputum. In this single-center prospective cohort study at Osaka Toneyama Medical Center, we analyzed 125 sputum samples from 115 patients with NTM pulmonary disease and 10 with non-NTM respiratory conditions. Samples were decontaminated using N-acetyl-L-cysteine-sodium hydroxide (NALC-NaOH) or succinic acid. We compared the reference culture method (mycobacterial culture plus whole-genome sequencing) and a culture-free direct target capture sequencing method. Core genome multi-locus sequence typing identified subspecies in both workflows, covering 186 mycobacterial species, including M. tuberculosis. The 115 NTM cohort specimens yielded 57 smear-positive and 93 culture-positive results. The identified subspecies included 48 Mycobacterium avium subsp. hominissuis, 22 Mycobacterium intracellulare subsp. intracellulare, 5 subsp. chimaera, 7 Mycobacterium abscessus subsp. abscessus, 5 subsp. massiliense, 1 M. tuberculosis, and 5 other NTM species. The culture-free method showed a high identification rate for smear-positive specimens (75.4%) but a low identification rate for smear-negative specimens (13.9%). NALC-NaOH pretreatment resulted in higher accuracy (90.5%) than did succinic acid pretreatment (66.7%). Thus, our culture-free subspecies-level identification method achieved high accuracy, especially in alkaline-treated smear-positive sputum samples, achieving rates above 90%. This method is recommended in clinical practice for patients who require rapid diagnosis and timely initiation of appropriate treatment, bypassing time-consuming culture steps.IMPORTANCEAccurate identification of Mycobacterium species and subspecies is crucial for effective treatment, as drug susceptibility and clinical outcomes vary significantly among them. However, conventional diagnosis relies on culture-based methods that can take several weeks, critically delaying appropriate therapy. This study validates a novel culture-free method using target capture sequencing for the comprehensive, subspecies-level identification of over 186 mycobacterial species directly from sputum specimens. Our findings revealed the high accuracy of this approach for smear-positive specimens, especially with alkaline pretreatment. This rapid method is applicable in clinical settings and enables timely and precise treatment decisions, greatly benefiting patients who require urgent intervention.