Probiotic bacteria isolated from stools of a tribal population (Tamil Nadu, India): in vitro functional characterisation and postbiotic potential
Thirteen bacterial isolates from stools of 25 tribal-community individuals demonstrated favourable in vitro probiotic properties — including >70% survival under simulated gastric-biliary conditions and 12–25 mm pathogen-inhibition halos — but no animal or human testing was performed, so clinical efficacy remains entirely unestablished.
| Outcome | Grade | Direction | Effect | Studies |
|---|---|---|---|---|
| Survival under simulated gastrointestinal conditions | D | ▲ Favorable | >70% survival (no IC, no comparator) | 1 |
| Pathogen inhibition (inhibition halo) | D | ▲ Favorable | 12–25 mm (no IC, no comparator) | 1 |
| Cell surface hydrophobicity | D | ▲ Favorable | 60%–80% (no IC, no comparator) | 1 |
| Short-chain fatty acid (SCFA) production | D | — Insufficient | qualitative only, no quantification reported | 1 |
| Protease activity | D | ▲ Favorable | 15–20 mm clearance (no IC, no comparator) | 1 |
| Erythrocyte membrane stabilisation | D | ▲ Favorable | 65%–82% (no IC, no comparator) | 1 |
| Safety profile (haemolysis, DNase) | D | ▲ Favorable | 0/13 haemolytic; 0/13 DNase-positive | 1 |
Context
Traditional tribal populations with non-Westernised diets may harbour microorganisms with metabolic capabilities not found in urbanised cohorts. Functional characterisation of indigenous strains is a necessary exploratory step before formulation development. This study does not test efficacy in any disease model.
What the study showed
The 13 isolates (mainly Lactiplantibacillus plantarum and Lacticaseibacillus rhamnosus) survived >70% under simulated gastric-biliary conditions. Cell surface hydrophobicity ranged 60%–80% and pathogen inhibition halos measured 12–25 mm. Protease activity produced 15–20 mm clearance zones and erythrocyte membrane stabilisation reached 65%–82%. No isolate was haemolytic or DNase-positive. No 95% CIs, p-values, comparative effect sizes, or standardised positive controls were reported.
How it was done
Observational/descriptive in vitro study. Stool samples were collected from 25 healthy volunteers at Mulluvadi village; 112 isolates were obtained by culture and 13 representative strains were selected by sequential functional screening. No protocol registration, sample-size calculation, or blinding was reported. Duration of assays was not specified.
Effect magnitude
No formal effect sizes (RR, OR, SMD) were calculated. Results are expressed as observed ranges in laboratory assays (e.g., 60%–80% hydrophobicity; 12–25 mm halos). Absence of standardised comparators and 95% CIs renders magnitude clinically uninterpretable.
Limitations
Exclusively in vitro study with no animal or human validation — evidence grade D. No comparator group (validated reference strains), no 95% CIs, no p-values, and no inferential statistical analysis. Donor sample extremely small (n=25) with limited demographic characterisation. Risk of bias not formally assessed (no RoB 2, ROBINS-I, or AMSTAR-2 applied). SCFA production not quantified by standardised analytical methods (e.g., gas chromatography). Sequential selection of 13 from 112 isolates without pre-specified transparent criteria may introduce selection bias.
In clinical practice
This study provides no basis for any clinical recommendation. All data are exclusively exploratory/in vitro. Clinicians must not infer therapeutic efficacy or patient applicability from these findings.
What is still missing
Animal models of dysbiosis are required next, followed by RCTs in humans measuring clinically relevant outcomes (e.g., inflammatory markers, microbiome composition, gastrointestinal symptoms). SCFA production should be quantified by gas chromatography with standardised comparators.