Sputum Microbiome Based on the Etiology and Severity of Nontuberculous Mycobacterial Pulmonary Disease

<b>Background</b>: Nontuberculous mycobacterial pulmonary disease (NTM-PD) is a chronic respiratory infection primarily caused by <i>Mycobacterium avium</i> complex (MAC) and <i>Mycobacterium abscessus</i>. These species differ markedly in antibiotic susceptibility and treatment response, yet the contribution of the respiratory microbiome to this clinical variability remains unclear. To date, however, comparative analyses of microbiome differences between MAC-PD and <i>M. abscessus</i>-PD and their associations with disease severity are limited. <b>Methods</b>: We conducted microbiome analysis of sputum from 37 patients with NTM-PD. Patients were antibiotic-naïve and classified into MAC-PD (n = 29) and <i>M. abscessus</i>-PD (n = 8) groups. Disease severity was determined using radiologic extent on chest computed tomography. Bacterial communities were profiled by 16S rRNA gene sequencing, and differential taxa and predicted functional pathways were analyzed using LEfSe and KEGG orthology databases. <b>Results</b>: Distinct microbiome profiles were observed between MAC-PD and <i>M. abscessus</i>-PD. Three anaerobic species-<i>Porphyromonas pasteri</i>, <i>Fusobacterium periodonticum</i>, and <i>Prevotella nanceiensis</i>-were significantly enriched in <i>M. abscessus</i>-PD (LDA effect size > 3, <i>p</i> < 0.05). Functional biomarker analysis revealed significant enrichment of the cobalamin (vitamin B12) biosynthesis pathway in patients with severe disease, while the C19/C18 steroid hormone biosynthesis pathway was enriched in those with mild disease (<i>p</i> < 0.05). <b>Conclusions</b>: In conclusion, our study demonstrates distinct differences in the respiratory microbiome between MAC-PD and <i>M. abscessus</i>-PD and identifies specific functional pathways associated with disease severity in NTM-PD. These findings highlight the potential value of microbial metabolic signatures as biomarkers for disease assessment.