The clinical value of metagenomic next-generation sequencing in the diagnosis of pulmonary tuberculosis and the exploration of lung microbiota characteristics

The lung microbiota plays a critical role in many important physiological processes and is linked with various pulmonary infectious diseases. The present study aimed to characterize the lung microbiota in patients with pulmonary tuberculosis (PTB), and to explore the association between the abundance of Mycobacterium tuberculosis complex (MTBC) and the lung microbiota. This retrospective study included 190 patients with MTBC infection. The enrolled patients were classified into three groups based on the abundance results of bronchoalveolar lavage fluid (BALF) mNGS: low [reads per ten million (RPTM) = 1 ~ 1000], medium (RPTM = 1001 ~ 10000) and high (RPTM > 10000). In the high-abundance group, there were more bilateral lobar involvement and symptoms of cavitation. In addition to mNGS, the highest positivity rates were T-spot (92.36%), GeneXpert (71.58%), culture (68.95%) and AFB smear (17.84%). The positive rates of culture, AFB smear and GeneXpert increased with the increase of MTBC abundance, and the positive rates were highest in the high-abundance MTBC group. Both the alpha and beta diversity showed significant difference between the three groups, with the high-abundance MTBC groups showed lowest alpha diversity. The increased abundance of MTBC positively associated with the longer time of hospital stay. To sum up, the lung microbiota of patients with PTB were significantly distinct between groups with different abundant levels of MTBC. Combined with imaging features, a high abundance of MTBC suggests the patient is more severely ill and has a poorer prognosis.