Metagenomic Analysis of Caseum of Tuberculosis Foci

The microbiota of the deep lung regions significantly differs from that of the upper respiratory tract by much lower biomass and dynamic diversity. In our previous studies we found that the biodiversity of the satellite microbiota of tuberculosis foci is sharply reduced in comparison with intact lung tissues. These findings allowed us to classify microbial communities in the caseous necrosis of tuberculomas into two types: (i) mycobacterial caseoma (tuberculoma), where 70% or more of the genomes correspond to Mycobacterium tuberculosis, and (ii) a polymicrobial community, where the concentration of M. tuberculosis varies from 0 to 10%. Using shotgun metagenomic sequencing, 14 tuberculomas from 13 patients were analyzed on a NextSeq 550 platform (Illumina). Taxonomic classification of short reads was performed using Kraken 2. The results show that, on average, 99.95% of the short reads belonged to human DNA or were unclassified. However, the classified reads related to bacterial genomes confirmed the concept that in many cases, tuberculomas contained polymicrobial communities that either replaced or supplemented the original mycobacterial microbiota of the caseous material.