Exploratory BALF analyses reveal a high diversity of microbiome in NTM lung disease and a low diversity of microbiome in bronchiectasis

<bold>Objectives:</bold> Nontuberculous mycobacterial lung disease (NTM-LD) and bronchiectasis have similar background lung structures. Both result in chronic persistent bacterial infection, but few studies have compared the microbiome composition of the two diseases. <bold>Methods:</bold> In this exploratory study, we recruited patients with clinically suspected NTM-LD, performed bronchoscopy and collected bronchoalveolar lavage fluids (BALF). Patients were assigned to NTM-LD and bronchiectasis according to the bacteriological results of bronchoscopy. <bold>Results:</bold> A total of 8 patients with NTM-LD and 11 patients with bronchiectasis were recruited. We compared the microbiome composition of BALF collected from them. In alpha diversity analysis, patients with NTM-LD presented a significantly higher Simpson index than those with bronchiectasis (H=5.734, P=0.0166). In beta diversity analysis, there were significant differences of Bray-Curtis distance (P=0.016) and Weighted UniFrac distance (P=0.002) between NTM-LD and bronchiectasis patients. A heat map analysis also showed the bacterial flora was clearly divided into two clusters by NTM-LD and bronchiectasis (Figure 1). It was also found that multiple characteristic strains of bacteria were significantly present in patients with NTM-LD. On the other hand, bacteria that were positive in culture tests in both NTM and bronchiectasis patients were not always detected in microbiome analysis. <bold>Conclusions:</bold> There was a clear difference in microbiome composition between NTM-LD and bronchiectasis, which share common lung structures, with microbiome diversity maintained under infection with NTM.