Probiotic Use in Gastrointestinal (G.I.T.) Infections

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1. Introduction

Gastrointestinal (GIT) infections — including acute infectious diarrhoea, antibiotic-associated diarrhoea (AAD), Helicobacter pylori-related disease, and Clostridioides difficile-associated diarrhoea (CDAD) — remain a major cause of global morbidity and healthcare utilisation, particularly among children and hospitalised adults. Management relies on rehydration, supportive care, and antimicrobial therapy where indicated; however, rising antimicrobial resistance and antibiotic-associated dysbiosis have intensified interest in adjunctive, non-antibiotic strategies. Probiotics are defined by the International Scientific Association for Probiotics and Prebiotics (ISAPP), building on the FAO/WHO definition, as live microorganisms that confer a health benefit on the host when administered in adequate amounts [1]. Commonly studied genera include Lactobacillus, Bifidobacterium, and the yeast Saccharomyces boulardii, acting through competitive exclusion, antimicrobial metabolite production, barrier enhancement, and immunomodulation [14,15] (Figure 1). A substantial body of randomised controlled trials, systematic reviews and meta-analyses has examined probiotics across acute infectious diarrhoea, AAD, CDAD prevention, adjunctive H. pylori eradication, and traveller's diarrhoea (TD) prevention, but conclusions have not been uniform; some earlier positive findings have been tempered by larger trials and updated reviews accounting for publication bias [2,3,8,9]. This review synthesises current evidence on probiotic use in gastrointestinal infections, summarising the strains and indications with the strongest data, the magnitude of reported effects, underlying mechanisms, and clinical caveats.

2. Methodology

A narrative review was conducted using PubMed, the Cochrane Library, and Google Scholar for publications from January 2003 to mid-2026, combining “probiotics” with “gastrointestinal infection,” “acute diarrhoea,” “antibiotic-associated diarrhoea,” “Clostridioides difficile,” “Helicobacter pylori,” and “traveller's diarrhoea.” Priority was given to Cochrane systematic reviews, meta-analyses, large multicentre RCTs, and guidelines from recognised gastroenterology/paediatric societies [2-13]. Inclusion criteria: human studies, English-language, a defined GIT infectious indication (acute infectious diarrhoea, AAD, CDAD, H. pylori infection, or TD), and a quantifiable outcome (duration, incidence, eradication rate, or relative/odds risk). In vitro and animal studies, case reports, and non-infectious indications (e.g., irritable bowel syndrome, inflammatory bowel disease) were excluded as outside the stated scope.

For each source, the probiotic strain(s), GIT indication, effect estimate (with 95% CI where available), and proposed mechanism were extracted and tabulated (Tables 1-3, Figures 1-2). Given the narrative, rather than formal PRISMA-based systematic, design, findings were synthesised qualitatively, with quantitative estimates drawn directly from the cited meta-analyses for illustrative comparison.

3. Results

Table 1 summarises the probiotic strains/formulations most frequently studied across the five GIT infection contexts identified, with their reported clinical effects.

Table 1: Major probiotic strains/formulations studied in gastrointestinal infections and their primary clinical indications Strain / formulation Primary GIT indication Reported clinical effect Ref. Lactobacillus rhamnosus GG Acute (largely viral) paediatric gastroenteritis Earlier meta-analyses: ~1-day shorter diarrhoea; large 2018 ED trial found no benefit 7, 8 Saccharomyces boulardii Antibiotic-associated diarrhoea; adjunct in CDAD/recurrent CDI Significant reduction in AAD incidence (21 RCTs); only agent with evidence for recurrent CDI 5, 6 Multi-strain Lactobacillus mixtures CDAD / AAD prevention during antibiotic exposure Pooled RR reduction in CDAD and AAD incidence vs placebo 4, 5 Multi-strain Lactobacillus + Bifidobacterium Adjunct to H. pylori eradication therapy Modest improvement in eradication rate; consistent reduction in antibiotic-related side effects 12 S. boulardii / Lactobacillus-Bifidobacterium combinations Prevention of traveller's diarrhoea (TD) Significant overall reduction in TD incidence; smallest effect size of all indications reviewed 13 Acute infectious diarrhea: The largest evidence base concerns acute infectious (largely viral) diarrhoea, mainly in children. The original Cochrane review by Allen et al. [2] (63 RCTs, >8,000 participants) found probiotics reduced the risk of diarrhoea persisting ≥3 days (RR 0.66, 95% CI 0.55-0.77) and shortened mean duration by roughly one day (Table 2, Figure 2). However, the 2020 update by Collinson et al. [3] (82 RCTs, 12,127 participants), after identifying substantial publication bias among smaller trials, concluded the overall evidence was no longer clinically convincing under GRADE assessment (Table 2).

Antibiotic-associated and C. difficile-associated diarrhea: For AAD, McFarland's meta-analysis [5] reported a pooled RR ≈ 0.43 favouring probiotics, with Lactobacillus combinations and Saccharomyces boulardii the most consistently effective. S. boulardii specifically reduced AAD incidence across 21 RCTs with no excess adverse events [6]. For CDAD prevention, Goldenberg et al. 4 (23 RCTs, 4,213 participants) found probiotics safe and effective, with the largest relative-risk reduction examined here (RR ≈ 0.36, 95% CI 0.26-0.51) (Table 2, Figure 2).

Fig 1: Pooled relative-risk estimates for probiotic supplementation across selected gastrointestinal infection outcomes (RR < 1.0 favours probiotics; 95% CI shown)

Table 2: Pooled effect estimates from key systematic reviews and meta-analyses of probiotic use in GIT infections Outcome Source review Trials / N Pooled estimate (95% CI) Direction Acute infectious diarrhoea (≥3 days) Allen et al., 2010 63 RCTs; ~8,014 RR 0.66 (0.55–0.77) Reduced risk Acute infectious diarrhoea (update) Collinson et al., 2020 82 RCTs; 12,127 No convincing effect (publication bias; GRADE) Uncertain Antibiotic-associated diarrhoea McFarland, 2006 Pooled RCTs RR ≈ 0.43 (0.31–0.58) Reduced risk C. difficile-associated diarrhoea Goldenberg et al., 2013 23 RCTs; 4,213 RR ≈ 0.36 (0.26–0.51) Reduced risk Traveller's diarrhoea prevention McFarland, 2007 12 treatment arms RR 0.85 (0.79–0.91) Reduced risk Paediatric acute gastroenteritis (ED)

Schnadower/Freedman, 943 + 886 children No significant reduction in moderate-severe AGE No effect Helicobacter pylori eradication: Adjunctive probiotics during standard triple/quadruple eradication therapy modestly improve eradication rates and, more consistently, reduce therapy-related adverse effects such as diarrhoea, nausea and vomiting [12]. Multi-strain Lactobacillus/Bifidobacterium combinations given for >2 weeks, before or alongside antibiotics, appear most beneficial (Table 1).

Traveller's diarrhea: McFarland's meta-analysis of 12 treatment arms [13] found probiotics significantly reduced TD risk (RR 0.85, 95% CI 0.79-0.91) — the smallest relative effect summarised here — with S. boulardii and specific Lactobacillus/Bifidobacterium combinations performing best (Table 1, Figure 2).

Paediatric trials and mechanisms: Two large 2018 multicentre placebo-controlled ED trials — Schnadower et al. 8 (L. rhamnosus GG, 943 children) and Freedman et al. [9] (L. rhamnosus/L. helveticus, 886 children) — found no significant reduction in moderate-to-severe gastroenteritis, despite earlier positive meta-analyses [7] (Table 2). The mechanisms underlying the effects above — competitive exclusion, antimicrobial production, toxin neutralisation, barrier enhancement, and immunomodulation 14,15 — are summarised in Figure 1 and Table 3, with their relative contribution varying by strain and infection context.

Fig 2: Schematic overview of proposed mechanisms by which probiotics counter enteric pathogens in gastrointestinal infections Table 3: Reported mechanisms of action of probiotics relevant to gastrointestinal infections Mechanism Description Example strains Competitive exclusion Competes for mucosal adhesion sites and nutrients, limiting pathogen colonisation Lactobacillus, Bifidobacterium spp.

Antimicrobial production Bacteriocins, organic acids and H2O2 inhibit growth of pathogenic organisms L. casei, multi-strain mixtures Toxin neutralisation Degrades/neutralises bacterial toxins, e.g. C. difficile toxins A and B Saccharomyces boulardii Barrier enhancement Upregulates tight-junction proteins and mucin secretion, reducing pathogen translocation Multi-strain formulations Immunomodulation Modulates cytokine profile, secretory IgA and regulatory T-cell responses Lactobacillus rhamnosus GG

4. Discussion

Probiotic efficacy in GIT infections is strain-, dose- and indication-specific rather than uniform. The largest relative-risk reductions were for CDAD (RR ≈ 0.36) 4 and AAD (RR ≈ 0.43) 5 prevention — contexts where the probiotic's task (limiting antibiotic-induced dysbiosis) aligns with competitive exclusion, antimicrobial metabolite production and toxin neutralisation, particularly by S. boulardii [6,15] (Figure 1). The smaller effect for TD (RR 0.85) 13 reflects the more heterogeneous, less predictable pathogen exposure during travel.

The evidence trajectory for acute infectious diarrhoea is instructive: earlier reviews [2] suggested moderate benefit, but the 2020 Cochrane update [3], incorporating large low-risk-of-bias trials and formally assessing publication bias, substantially weakened this conclusion — reinforced by two large 2018 paediatric ED RCTs [8,9] that found no benefit for L. rhamnosus GG or L. rhamnosus/L. helveticus combinations despite earlier positive meta-analyses [7]. This illustrates how pooled small-trial estimates can overstate effects not replicated in adequately powered studies. Clinically, ESPGHAN/ESPID [10] and AGA [11] guidelines reflect this nuance, avoiding blanket recommendations for acute paediatric gastroenteritis while supporting strain-specific use (e.g., S. boulardii or Lactobacillus mixtures for AAD/CDAD prevention) where evidence is stronger. For H. pylori, probiotics are best framed as an adjunct reducing side effects and supporting antibiotic adherence rather than a substitute for standard regimens [12].

Mechanistically (Figure 1, Table 3), this variability reflects strain specificity: toxin neutralisation and competitive exclusion are well-documented for specific organisms (e.g., S. boulardii against C. difficile toxins 15) but cannot be generalised across all “probiotic” products, which differ in species, strain, dose and viability. Safety data were reassuring for immunocompetent hosts, with no significant excess adverse events [4,6], though probiotic-associated bacteraemia/fungaemia in severely immunocompromised patients warrants caution [11].

Limitations include this review's narrative rather than systematic design, reliance on published pooled estimates rather than individual-patient data, and cross-study heterogeneity in strains, doses and formulations, which limits direct comparability of the Figure 2 estimates.

5. Conclusion

Probiotic supplementation has a defensible, evidence-based role in selected gastrointestinal infections — most notably prevention of antibiotic-associated and Clostridioides difficile-associated diarrhoea, and as an adjunct reducing side-effect burden during Helicobacter pylori eradication. Evidence for acute infectious and traveller's diarrhoea is more modest and increasingly nuanced following recent large trials. Recommendations should be strain- and indication-specific rather than generic, favouring formulations (e.g., Saccharomyces boulardii, specific Lactobacillus combinations) with the strongest evidence for the intended indication, with future research prioritising adequately powered, strain-specific trials with standardised outcomes.