Strain-Specific Systematic Review with Meta-Analysis of Probiotics Efficacy in the Treatment of Irritable Bowel Syndrome

<b>Background</b>: Many probiotic strains have been studied in relation to irritable bowel syndrome (IBS). The aim of this study was to identify probiotic strains demonstrating efficacy in the management of IBS based on meta-analyses of randomized placebo-controlled trials (RPCTs). <b>Methods</b>: This systematic review was registered in the PROSPERO database (CRD420251047092). Searches were conducted in PubMed and Scopus on 8 April 2025. Additional completed studies with available results were identified through ClinicalTrials.gov. An additional search of the Cochrane Central Register of Controlled Trials (CENTRAL), including records indexed in EMBASE, was conducted in December 2025 and did not identify any additional studies. RPCTs were included if they evaluated single-strain probiotics without additional active components compared with a placebo in patients with IBS. Studies whose results could not be meta-analyzed were excluded. <b>Results:</b> A total of 2643 records were identified; 32 articles evaluating 10 probiotic strains were included in the meta-analyses. Meta-analyses demonstrated the efficacy of <i>Bifidobacterium longum</i> (formerly <i>Bifidobacterium infantis</i>) 35624, <i>Lactobacillus rhamnosus</i> GG, <i>Lactiplantibacillus plantarum</i> 299v (DSM 9843), <i>Saccharomyces cerevisiae</i> CNCM I-3856, and <i>Bacillus coagulans</i> Unique IS2 (MTCC 5260) in improving key IBS symptoms. Meta-analyses also demonstrated that <i>Bacillus coagulans</i> MTCC 5856 improved quality of life for those with IBS. Conflicting results were observed for <i>Saccharomyces boulardii</i> CNCM I-745. Meta-analyses did not demonstrate the efficacy of <i>Escherichia coli</i> Nissle 1917, <i>Lactobacillus gasseri</i> BNR17, or <i>Lactobacillus casei</i> Shirota. <b>Conclusions:</b> Several probiotic strains demonstrated efficacy in the treatment of IBS in meta-analyses of RPCTs.