Stronger gut microbiome modulatory effects by postbiotics than probiotics in a mouse colitis model

The study addresses whether postbiotics, defined as preparations of inanimate microorganisms and/or their components, can confer benefits comparable to or greater than probiotics in ulcerative colitis while posing fewer safety risks. Probiotics are widely used but can raise safety concerns in critically ill patients, including risks of bacteremia and potential transfer of virulence or antibiotic resistance genes. Postbiotics offer stability and safety advantages by removing viability concerns. Ulcerative colitis (UC) involves complex interactions among environmental, genetic, microbial, and immune factors, with the gut microbiota playing a pivotal role. Prior studies show probiotics can attenuate UC symptoms, and emerging data suggest postbiotics may reduce UC risk, but no direct comparison has been made. The authors therefore aimed to directly compare probiotics and postbiotics prepared from the same strain, Bifidobacterium adolescentis B8589, in a DSS-induced colitis mouse model to evaluate effects on disease phenotype, gut microbiota diversity/composition, and metagenomic functional potential.

The paper contextualizes probiotic use and associated safety concerns, citing increased mortality in a probiotic arm of severe acute pancreatitis and rare bloodstream infections linked to probiotic administration. It reviews the ISAPP definition and purported advantages of postbiotics, including reduced safety risks, absence of horizontal gene transfer from live organisms, and storage stability. For UC, the authors summarize evidence implicating the gut microbiota and prior rodent studies demonstrating probiotic efficacy in DSS-induced colitis (Table 1), including improvements in inflammatory markers, barrier function, and microbiota composition across various strains (e.g., Lactobacillus, Bifidobacterium, Akkermansia, Clostridium butyricum, Saccharomyces boulardii). They also cite emerging postbiotic-related studies (e.g., bacterial components, extracellular vesicles, enzymes) that ameliorate colitis or promote mucosal healing. The identified gap is the lack of direct, parallel comparisons of probiotics versus postbiotics from the same strain in the same experimental setting.

Design: Male SPF C57BL/6J mice (6–8 weeks, 18–22 g) were acclimatized for one week and then randomized into four groups (n=7/group): Control, DSS, Postbiotic, and Probiotic. UC induction: DSS 2.5% (w/v; 36–40 kDa) in drinking water ad libitum for 7 days. Interventions (following DSS phase): daily oral gavage for 7 days with 0.2 mL sterile saline (Control and DSS), postbiotic suspension (non-viable B. adolescentis B8589, 2×10^9 cells/day), or probiotic suspension (live B. adolescentis B8589, 2×10^9 CFU/day). Outcomes: Daily body weight; disease activity index (DAI) from weight loss, stool consistency, and fecal occult blood; colon length at sacrifice (day 15); histopathology of mid-colon (H&E staining, standardized histological scoring). Fecal samples collected aseptically and stored at −80 °C for metagenomics. Metagenomics: DNA extracted with QIAamp Fast DNA Fecal Mini Kit; library prep with NEBNext Ultra DNA Library Prep; Illumina NovaSeq 6000 paired-end 150 bp. Quality control with KneadData; host read removal via Bowtie2; taxonomic profiling by mOTUs; functional profiling by HUMAnN with UniRef90 and MetaCyc pathway mapping. Statistics: R software; PCoA (Bray–Curtis) with vegan; Adonis for beta-diversity; between-group comparisons with Student’s t-test or Wilcoxon rank-sum test; multi-group with ANOVA or Kruskal–Wallis followed by pairwise tests; P<0.05 significant. Ethics: Approved by Experimental Animal Ethics Committee of Inner Mongolia Agricultural University; conducted under NIH guidelines.

- Disease phenotype: DSS caused weight loss and disease signs. Postbiotic and probiotic interventions did not significantly improve body weight loss or colon length and showed non-significant DAI reductions; however, both significantly reduced histological scores versus DSS (P<0.05), indicating amelioration of colitis-associated tissue damage. - Alpha diversity: Shannon and Simpson indices were numerically reduced in DSS and restored numerically by postbiotics but not probiotics; differences were not statistically significant. - Beta diversity: Significant divergence between Control and DSS (Adonis R^2=0.195, P=0.011). Postbiotic versus DSS showed a significant difference (R^2=0.158, P<0.024), while Probiotic versus DSS did not (R^2=0.068, P=0.561), indicating stronger postbiotic effects on community structure. - Taxonomic composition: Eight phyla identified; Bacteroidetes (57.24%) and Firmicutes (22.92%) dominant. No significant phylum-level differences between DSS and Postbiotic or Probiotic groups. At species level (117 species total), 13 differential species in Postbiotic vs DSS and 6 in Probiotic vs DSS. Both treatments had fewer Bacteroidaceae sp. and more Escherichia coli, Peptostreptococcaceae sp., and Bacteroides thetaiotaomicron vs DSS (P<0.05). Postbiotic group uniquely showed increases in Bacteroides intestinalis, Lactobacillus animalis/murinus, and Romboutsia timonensis, and decreases in Bacteroidales bacterium M12, Muribaculum intestinale, and Bacteroidaceae sp. (P<0.05). - Functional metagenomics: 286 MetaCyc pathways detected; 217 (81.3%) common to DSS, Probiotic, and Postbiotic; pathways unique to DSS (15), Probiotic (5), Postbiotic (2). Differential pathways vs DSS: Control (40), Postbiotic (144), Probiotic (61), indicating a stronger modulatory effect by postbiotics. - Microbe–function associations: In postbiotic-fed mice, most top metabolic pathways were positively correlated with Bacteroidales bacterium M9 and Muribaculaceae sp., and negatively with Helicobacter bilis, Bacteroides intestinalis, and Escherichia coli. Probiotic-fed mice showed fewer/weaker correlations, with positive associations mainly with Akkermansia muciniphila and Bacteroidales bacterium M10, and negative with Bacteroides intestinalis and Bacteroides uniformis. Several shared taxa exhibited opposite correlation directions between postbiotic and probiotic groups, supporting divergent ecosystem effects.

The study directly addressed whether postbiotics can match or exceed probiotics in mitigating DSS-induced colitis and modulating the gut microbiome when derived from the same strain. Both interventions reduced histopathological damage, indicating comparable clinical phenotype improvement. However, postbiotics exerted stronger effects on gut microbiota structure (beta diversity), species-level composition, and functional pathway profiles, suggesting that inactivated cells and/or their components may produce more pronounced ecosystem-level modulation than live cells in this model and regimen. These findings align partly with prior probiotic studies that often found limited phylum-level shifts but species-level and functional changes, and they expand the literature by providing a head-to-head comparison. The divergence in microbe–function correlation patterns indicates distinct network re-wiring under postbiotic versus probiotic conditions, which could underpin differences in host effects. Given known safety advantages of postbiotics (no risk of bacteremia, lower risk of gene transfer, improved stability), the results support prioritizing postbiotics as biotherapeutics for UC management, while emphasizing the need to elucidate mechanisms and validate in larger preclinical and clinical settings.

Using Bifidobacterium adolescentis B8589-derived preparations, both probiotics and postbiotics attenuated DSS-induced colitis histopathology, but postbiotics more robustly modulated gut microbial community structure, composition, and metagenomic functional potential. These data support postbiotics as promising next-generation biotherapeutics for UC, potentially preferable to probiotics due to reduced safety concerns and stronger microbiome modulatory effects observed here. Future work should include mechanistic studies to identify active components and pathways, standardized protocols for dosing and animal models, rigorous quantification of live vs dead cells in preparations, strain screening for potency, and large-scale preclinical and human clinical trials to confirm efficacy and safety.

- Mechanistic ambiguity: The precise mechanisms by which probiotics and postbiotics improved colitis and altered the microbiome were not delineated. - Safety not directly tested: Although postbiotics are presumed safer, this study did not experimentally assess safety differences. - Model and regimen constraints: Lack of significant effects on body weight, DAI, and colon length may reflect strain-specific effects, dosing, timing, or DSS protocol differences versus other studies. - Generalizability: Results are in a single mouse strain and model; translation to humans requires clinical validation. - Standardization gaps: Variability in dosing, duration, and model construction across studies complicates comparisons; need for universal assessment standards. - Strain specificity: Effects likely vary by strain; broader screening is needed. - Enumeration issue: Probiotic preparations contain both live and dead cells; accurate quantification of each fraction is necessary to disentangle contributions.