Research on Gut Microbiota Features and Potential Biomarkers in Patients with Pulmonary Tuberculosis

(1) Objective: To characterize structural and functional alterations of gut microbiota in patients with newly diagnosed active pulmonary tuberculosis (ATB), screen differential bacterial taxa associated with Mycobacterium tuberculosis (MTB) infection, and explore tuberculosis-related microbial metabolic alterations via predictive functional profiling. (2) Methods: Fresh morning fecal samples were collected from 33 treatment-naive patients with newly diagnosed ATB (ATB group) and 30 healthy controls (HC group). 16S rRNA gene high-throughput sequencing was performed to compare intergroup differences in gut microbial α/β diversity, taxonomic composition, and predicted KEGG functional profiles. Receiver operating characteristic (ROC) curve analysis was conducted to evaluate the internal discriminative ability of candidate differential genera in this single small cohort. (3) Results: The ATB group showed significantly lower gut microbial α-diversity than healthy controls (all P < 0.05). Principal coordinate analysis (PCoA) based on Bray-Curtis distances combined with permutational multivariate analysis of variance (PERMANOVA) revealed significant overall dissimilarity of gut microbial community structure between the two groups (R² = 0.31, p = 0.005). At the phylum level, the relative abundances of Firmicutes and Bacteroidetes were higher, while Proteobacteria was less abundant in ATB patients relative to HC. At the genus level, Streptococcus, R. gnavus and Parabacteroides were significantly enriched in ATB patients, whereas Bifidobacterium, Pseudomonas, Megamonas and Faecalibacterium were depleted. Linear discriminant analysis effect size (LEfSe) analysis uncovered group-specific signature taxa, with pro-inflammatory genera Streptococcus and R. gnavus markedly enriched in the ATB group. ROC analysis yielded area under the curve (AUC) values of 0.836 for Streptococcus and 0.805 for R. gnavus. Predictive KEGG functional analysis demonstrated obvious intergroup differences in microbial metabolism, with purine and pyrimidine nucleotide metabolism pathways significantly upregulated in the ATB group. (4) Conclusions: Treatment-naive patients with ATB exhibited reduced gut microbial diversity in this small cohort. The enrichment of Streptococcus and R. gnavus, as well as the upregulation of purine and pyrimidine metabolic pathways, are all associated with active MTB infection.