Probiotics are used for both generally healthy consumers and in clinical settings. However, theoretical and proven adverse events from probiotic consumption exist. New probiotic strains and products, as well as expanding use of probiotics into vulnerable populations, warrants concise, and actionable recommendations on how to work toward their safe and effective use. The International Scientific Association for Probiotics and Prebiotics convened a meeting to discuss and produce evidence-based recommendations on potential acute and long-term risks, risks to vulnerable populations, the importance for probiotic product quality to match the needs of vulnerable populations, and the need for adverse event reporting related to probiotic use. The importance of whole genome sequencing, which enables determination of virulence, toxin, and antibiotic resistance genes, as well as clear assignment of species and strain identity, is emphasized. We present recommendations to guide the scientific and medical community on judging probiotic safety. What is the context? Probiotics, available to healthy consumers as both dietary supplements and foods, are also used by some patient populations. The goal of this paper is to determine if any new factors have emerged that would impact current views about probiotic safety for both these populations. What is new? The authors conclude that established practices are sensibly addressing factors important to the safety of traditional probiotics used by the general population. They also make recommendations regarding emerging safety considerations. Probiotics targeted for patient populations should undergo stringent testing to meet quality standards appropriate for that population, preferably verified by an independent third party. The safety of probiotics derived from species without a history of safe use must be considered on a case-by-case basis. Research is needed to address some gaps, for example which best animal models to use for safety assessment of live microbes, the possibility of antibiotic resistance gene transfer via transformation, and potential impact of probiotic-induced changes in microbiomes, interactions with drugs, and probiotic colonization. What is the impact? Probiotics of sufficient quality for patient populations are being developed and should be used accordingly. Long-term safety assessments for probiotics should be consistent with, and not more stringent than, current regulatory requirements for biologic drugs, including fecal microbial transplants. Rigor in collecting and reporting data on adverse events is needed. The authors confirm the need for understanding the entire genetic makeup of a probiotic as a cornerstone for assessing its safety.

This randomized, double-blind, placebo-controlled, multi-center study investigated the clinical efficacy of two probiotic strains on abdominal pain severity and symptomology in irritable bowel syndrome (IBS). Three hundred and thirty adults, aged 18 to 70 years, with IBS according to Rome IV criteria were allocated (1:1:1) to receive placebo, Lactobacillus acidophilus DDS-1 (1 × 10¹⁰ CFU/day) or Bifidobacterium animalis subsp. lactis UABla-12 (1 × 10¹⁰ CFU/day) over six weeks. The primary outcome was the change in Abdominal Pain Severity - Numeric Rating Scale (APS-NRS). Over the intervention period, APS-NRS was significantly improved in both probiotic groups vs. placebo in absolute terms (DDS-1: −2.59 ± 2.07, p = 0.001; UABla-12: −1.56 ± 1.83, p = 0.001) and in percentage of significant responders (DDS-1: 52.3%, p < 0.001); UABla-12 (28.2%, p = 0.031). Significant amelioration vs. placebo was observed in IBS Symptom Severity Scale (IBS-SSS) scores for L. acidophilus DDS-1 (−133.4 ± 95.19, p < 0.001) and B. lactis UABla-12 (−104.5 ± 96.08, p < 0.001) groups, including sub-scores related to abdominal pain, abdominal distension, bowel habits and quality of life. Additionally, a significant normalization was observed in stool consistency in both probiotic groups over time and as compared to placebo. In conclusion, L. acidophilus DDS-1 and B. lactis UABla-12 improved abdominal pain and symptom severity scores with a corresponding normalization of bowel habits in adults with IBS.

Objective: To investigate the clinical efficacy of a multi‐strain probiotic product on bowel habits and microbial profile in participants with functional constipation.Methods: This was a randomized, double‐blind, placebo‐controlled and parallel‐arm study. Altogether 94 otherwise healthy adults aged 18 to 65 years with symptoms of functional constipation were randomized as part of the intention‐to‐treat population. The participants received a placebo or the probiotic product (1.5 × 10¹⁰ CFU/day), consisting of Lactobacillus acidophilus DDS‐1, Bifidobacterium animalis subsp. lactis UABla‐12, Bifidobacterium longum UABl‐14 and Bifidobacterium bifidum UABb‐10 over 4 weeks. Outcomes included the patient assessment of constipation‐symptom (PAC‐SYM) questionnaire, stool frequency and consistency, and microbial profile.Results: There were no significant between‐group differences in the PAC‐SYM score, despite significant within‐group differences (P < 0.001) over the study period. The probiotic group showed a faster normalization of stool frequency and consistency, with most participants achieving a normalized profile after 1 week. Fecal samples of the probiotic group exhibited higher relative abundance of Ruminococcaceae (P = 0.0047), including the Ruminococcus genus, and lower relative abundance of Erysipelotrichaceae (P = 0.0172) at end‐point compared with baseline. Placebo group samples showed similar abundance profiles over the study, with the exception of Clostridiaceae, which was lower at the study end‐point (P = 0.0033). Among treated participants, all four probiotic strains were significantly more abundant after the intervention.Conclusions: No significant differences were observed in symptomology, with both groups showing a more than 20% improvement. However, the probiotic helped modulate bowel function earlier than the placebo, with a corresponding shift to a more fibrolytic microbiota.