Diabetes reshapes the gut during tuberculosis

People who have both diabetes and tuberculosis often get sicker and respond less well to treatment, and researchers suspect the gut microbiome may play a role. Led by Ranjan Kumar Nanda, the study used a mouse model to look for those gut changes. The team induced diabetes in C57BL/6 mice with Nicotinamide (NA) and streptozotocin (STZ), then exposed the animals to Mycobacterium tuberculosis H37Rv by aerosol at a dose of 100–120 CFU. The researchers collected faecal samples at three time points: two days before infection and at 3 and 8 weeks post-infection (wpi). They compared mice with both diabetes and tuberculosis (DMTB) to mice with tuberculosis alone (TB) to see whether diabetes changed the gut bacterial community or the small molecules those bacteria produce. To do this, they used 16S rRNA sequencing to profile which bacteria were present and gas chromatography-time of flight-mass spectrometry (GC-TOF-MS) to measure the mix of faecal metabolites. The study was designed to reveal whether specific microbes or metabolites are linked to the combined disease and might explain the atypical progression seen in people with both conditions.

The results showed clear gut dysbiosis in the diabetic tuberculosis group. At 3 wpi, 16 bacterial genera were significantly different between the DMTB and TB groups, and by 8 wpi that number fell to 11 genera. Metabolically, the team identified 93 faecal metabolites in total. Of these, 11 metabolites at 3 wpi and 10 metabolites at 8 wpi were significantly deregulated in DMTB compared with TB (log2 FC > ±1.0, p < 0.05). One notable finding was a negative correlation between faecal valeric acid levels in DMTB mice and the abundances of several bacterial taxa: Coriobacteriaceae, Granulicatella, Veillonella, Achromobacter, Erysipelatrichaceae, Atopobiaceae, Citrobacter, and Lactiplantibacillus. Overall, correlations between microbiota and metabolites were stronger in DMTB comorbidity than in TB alone. The researchers also found a phylogenetic distance-dependent synchrony in amino acid metabolism across five clades, each containing three or more bacterial genera, linking bacterial relatedness to shared metabolic patterns.

These findings matter because they identify specific microbes and small molecules that change when diabetes and tuberculosis occur together. The changes in bacterial genera and in metabolites such as valeric acid suggest biological connections that could impair immune responses or influence disease progression. Importantly, the study points to concrete microbial and metabolic targets that might be developed into adjunctive treatments: the authors suggest some of the identified microbes and metabolic products could serve as prebiotic or probiotic candidates to aid recovery in DMTB comorbid conditions. While the work used a mouse model and further research will be needed to translate the results to people, the combined use of 16S rRNA sequencing and gas chromatography-time of flight-mass spectrometry (GC-TOF-MS) highlights a pathway for testing targeted interventions aimed at restoring a healthier gut environment in patients with both diabetes and tuberculosis.