Irritable bowel syndrome (IBS) is a widespread chronic functional gastrointestinal disorder affecting individuals worldwide. In some developed countries, it is more commonly diagnosed in women than in men. The diagnosis relies on the ROME IV criteria, which define IBS by symptoms such as irregular bowel movements—ranging from constipation to diarrhea—abdominal pain or discomfort that eases after passing gas or stool, and the exclusion of underlying organic conditions like inflammatory bowel disease (IBD), celiac disease, and colorectal cancer (1, 2). Symptoms must have been present for at least 6 months before diagnosis and follow specific clinical patterns. IBS is categorized based on the dominant symptomatology into IBS with diarrhea (IBS-D), IBS with constipation (IBS-C), and a mixed type (IBS-M) characterized by alternating constipation and diarrhea (2, 3). Additionally, psychological factors significantly influence the onset, persistence, treatment-seeking behavior, and response to therapies (4–6).

The impact of IBS on the quality of life of affected individuals is not negligible. IBS is often associated with other comorbidities such as pain syndromes, migraine, depression, and visceral sensitivity. The impact of IBS on quality of life is considered comparable to that of other chronic diseases that are more widely recognized by the population, such as diabetes mellitus and hepatitis. Moreover, since there is currently no treatment capable of curing individuals affected by IBS, symptom improvement remains the most important goal. This is especially crucial because when symptoms improve, quality of life consequently improves, allowing affected individuals to lead a life as normal as possible (3). Among the various elements and strategies involved in the development and management of IBS, dietary, pharmacological, nutraceutical, and probiotic approaches have been proposed (1, 7, 8). In particular, nutraceuticals and botanical food supplements commonly used for weight management have been shown to exert prebiotic effects, modulating key bacterial populations such as Bifidobacterium spp., Lactobacillus spp., Akkermansia muciniphila, and Faecalibacterium prausnitzi, which are implicated in gut health and metabolic balance (9). These findings suggest that certain nutraceutical compounds may play a role in IBS management through microbiota modulation. Probiotic approaches have progressively shifted over the years from more generalist strategies to solutions increasingly tailored to specific objectives, introducing concepts such as bacterial therapy (10), bioprotic therapy, or precision probiotics (11). Recent studies have shown that multi-strain preparations containing Lactobacillus spp., Enterococcus faecium, and Saccharomyces boulardii can significantly reduce IBS symptoms, especially in patients with SIBO, improving abdominal pain, stool consistency, and overall satisfaction with intestinal function, although some methodological limitations have been acknowledged (12). Martoni et al. (13) evaluated the effects of Lactobacillus acidophilus DDS-1 and Bifidobacterium lactis UABla-12 on IBS symptoms. Both probiotics significantly improved abdominal pain, symptoms, and quality of life, with Lactobacillus acidophilus DDS-1 showing a higher response rate (52.3%) compared to Bifidobacterium lactis UABla-12 (28.2%). Additionally, both probiotics normalized stool consistency over time. Considering the natural evolution in the use of probiotics, the aim of this study is to investigate whether a specific, precision-based probiotic strategy, employing dedicated bacterial strains, can effectively manage symptoms in IBS-C and IBS-D patients, thus providing new insights into the real-life application of targeted microbiota modulation.

Probiotics, by modulating the intestinal microbiota, can be useful in various conditions, improving metabolic aspects, reducing subclinical inflammation, and positively influencing the onset and progression of oncological diseases. Similarly, nutraceuticals like berberine, through microbiota modulation, could complement these benefits (14). In addition, probiotics have garnered significant interest for the treatment of various intestinal conditions. They have shown effectiveness in reducing the duration of acute infectious diarrhea, whether bacterial or viral in origin, as well as in preventing traveler’s diarrhea. Studies have also highlighted benefits in treating acute diarrhea in children, with a significant reduction in the number of days of illness. Moreover, probiotic supplementation during Helicobacter pylori treatment can improve eradication rates, reduce side effects of the therapy, and alleviate associated clinical symptoms. However, the results should be interpreted with caution, given the heterogeneity among the studies included in this analysis (15). In this meta-analysis (16), 15 RCTs with 2,963 participants showed that Lactobacillus GG significantly reduces the duration of diarrhea (−1.05 days) compared to placebo. The best results were obtained with daily doses ≥10¹⁰ CFU, especially in patients treated in Europe. However, due to methodological limitations, the results should be interpreted with caution (17). Although probiotics have shown some potential in various clinical fields, current evidence does not support their use in the management of functional constipation in children: a recent review of randomized trials found no significant benefits compared to placebo or laxative monotherapy, highlighting the need for further studies to define optimal strains, doses, and treatment durations (18). Experimental evidence suggests that changes in the gut microbiome, caused by environmental or dietary factors, may play a role in the etiopathogenesis of IBD. Probiotics, such as Lactobacillus and Bifidobacterium strains, act by suppressing pathogen growth, modulating the immune system, and improving the intestinal barrier (19). A promising advancement in this area is the genetic engineering of Escherichia coli Nissle 1917 (ECN), which has been modified to overexpress antioxidant enzymes like catalase and superoxide dismutase, potentially enhancing its ability to treat intestinal inflammation and improve gut health (20, 21).

Among the various approaches proposed for managing IBS, the low FODMAP diet is currently one of the most effective strategies. Literature reviews encompassing several thousand patients, have demonstrated a significant reduction in associated symptoms and symptom severity (8, 22). In the absence of celiac markers, some IBS patients may benefit from a gluten-free diet (GFD). Although the mechanism is not clear, studies suggest that gluten may increase intestinal permeability in IBS-D. However, the reduction of fructans in the GFD could be the main cause of the observed benefits, making it as useful as the low FODMAP diet (23). In a systematic review, Ley et al., analyzed different intervention strategies and reported that a low FODMAP diet is associated with a symptom reduction of 70.8%, while probiotic treatment is associated with a reduction of 65.1%. The combination of a low FODMAP diet and probiotic treatment leads to an 80.4% reduction in symptoms. Considering the reduction in IBS-SSS, the low FODMAP diet is linked to a 90.5% decrease in the score, while probiotic treatment results in a 62.3% reduction, and the combination of both treatments leads to a 90.5% reduction, proving to be the most effective solution (22). Given these findings, the use of probiotics with a targeted approach in IBS treatment represents a particularly promising area of investigation. Moreover, rifaximin, a nonsystemic gut-selective antibiotic, has demonstrated efficacy in clinical trials for improving global symptoms, bloating, abdominal pain, and stool consistency in patients with IBS-D. Its effects on gut microbiota are modest and transient, suggesting symptom relief may involve mechanisms beyond microbial modulation (23, 24).

When considering the incidence of IBS in the two analyzed subtypes, it is important to discuss the crucial role of age: in the systematic review by Pittayanon et al. (25), a significant prevalence is observed in adult subjects (aged between 20 and 50 years), while only three studies included pediatric participants and two did not report the age of participants. It is also important to highlight that more than 40% of the included studies did not specify whether case and control groups were age-matched, thus limiting conclusions regarding the influence of age. Further data helping to better delineate the phenomenon can be found in the study by Wilkins et al. (26), which indicates that the peak incidence of IBS occurs between the ages of 20 and 39. This is consistent with the statements found in the Rome IV criteria, where the typical age of onset for IBS is between 20 and 40 years, with a progressive decline after age 50. It is also noted that, although less commonly diagnosed after age 60, the disorder may persist if previously established (27).

A total of 24 subjects with diarrhea-predominant IBS (IBS-D) took the supplement CBM588 at a dosage of 3 tablets per day for 3 consecutive months, while 27 subjects with constipation-predominant IBS (IBS-C) took 1 stick of the supplement W11 for the same period. The group treated with CBM588 had a mean age of 54.4 ± 19.8 years (min-max 23–86), while the group treated with W11 had a mean age of 55.3 ± 20.2 years (min-max 18–85). Differences between the two groups were tested using an independent samples t-test, and no statistically significant differences were identified in any case, allows us to perform comparisons between the two groups. The sample characteristics are reported in Table 1.

The mean differences between post- and pre-treatment were first evaluated for each individual supplement and were assessed both in relation to the individual items and the final score of the IBS-SSS questionnaire. Using GLM, time effect was statistically significant for all scores, indicating a clear reduction in IBS severity scores in the post-treatment period. These results are reported in Table 2, where Cohen’s d coefficient for the estimate Effect Size is interpreted as follows: 0.2 small, 0.5 medium, 0.8 large (46).

To gain an even clearer view of the decrease in the score for each individual item, the data presented have been gathered in Figures 1, 2.

Since all individual items of the SSS questionnaire are significant, the same applies to the final scores, presented in Figure 3.

Regarding the W11 supplement, in addition to the significance observed between pre- and post-treatment scores, a significant effect of time * age was identified for the variables: bloating (F = 8.36, p = 0.008), interference with life in general (F = 6.40, p = 0.02), and IBS-SSS total score (F = 7.56, p = 0.01). This indicates that the evolution of bloating symptoms, interference with daily life, and the total score over time varies depending on the subjects’ age. The impact of the time factor, and thus the improvements following treatment in relation to these variables, differs based on age. Regarding the CBM588 supplement, a significant effect of the time on the following variables: bloating (F = 4.63, p = 0.04), interference with life in general (F = 6.40, p = 0.02), and total score (F = 4.73, p = 0.04), indicating a significant influence of time on these variables, suggesting a beneficial effect of the CBM588 supplement. Interesting between-subject effect for age was found on abdominal pain frequency (F = 12.17, p = 0.002), Bloating (F = 16.17, p = 0.001), dissatisfaction of bowel habits (F = 10.72, p = 0.004), total score (F = 15.40, p = 0.001). Indicating that these variables are significantly influenced by age, independently of the treatment and time.

Figure 4 provides a schematic summary of the study design and the main findings.

In this study, we analyzed the efficacy of Clostridium butyricum CBM588 and Bifidobacterium longum W11 in managing IBS in its IBS-D and IBS-C variants, respectively. Both strains demonstrated good efficacy in alleviating symptoms and improving clinical scores, without significant side effects. A key innovative aspect of this study is the approach that considers the dual nature in which IBS can manifest itself. One of the firsts findings concerns the relationship between age and symptom perception prior to treatment. In the group treated with CBM588, regression analysis showed that younger individuals reported more pronounced symptoms—such as dissatisfaction with bowel habits, more frequent abdominal pain, and greater interference with daily life—which tended to decrease with age (Figure 4). This may be explained by lifestyle differences: IBS-D may be more disruptive for younger individuals who typically lead busier lives and spend more time away from home, increasing their perception of discomfort.

In contrast, within the group treated with W11, elderly participants experienced significant improvements in bloating (p < 0.01) and interference with daily life (p < 0.05). The greater reduction in bloating was anticipated, as this symptom tends to be more pronounced with age, as shown in Figure 4 and supported by regression analysis comparing pre-treatment scores with symptom change (delta scores). For both supplements, the reduction in symptom scores after treatment was strongly correlated with baseline severity (Figures 6, 7). This indicates that a higher pre-treatment score results in a greater improvement in symptom perception, leading to a reduction in the interference of IBS symptoms with daily life and overall quality of life. This highlights how efficacy is closely correlated with the initial severity of symptoms (as indicated in Figures 6, 7). Interest in this type of intervention is growing, with several studies exploring the role of probiotics and dietary strategies in IBS management. These approaches act both at the organ level and on the gut microbiota, generating substantial data suitable for reviews and meta-analyses (7, 22). IBS, when correctly diagnosed according to Rome IV criteria, affects 3–5% of the global population and significantly impacts quality of life, healthcare resource use, and productivity (47). Approaches that target the gut microbiota are especially relevant, given its role in modulating immune and inflammatory responses and preserving intestinal epithelial function (48, 49). Maintaining a balanced microbiota, particularly with appropriate levels of Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria (49) is crucial, along with the presence of beneficial strains such as Lactobacilli and Bifidobacteria (50). Recent studies have highlighted the microbiota’s involvement in intestinal motility, visceral sensitivity, and even brain function, underscoring a bidirectional gut-brain communication pathway involving immune, metabolic, and neurological signals (51). These mechanisms align with the known effects of C. butyricum CBM588 and B. longum W11, especially in IBS patients who often exhibit reduced microbial diversity, increased pro-inflammatory species, and decreased populations of anti-inflammatory, butyrate-producing bacteria (52). Notably, IBS-D has also been associated with small intestinal bacterial overgrowth (SIBO) (53). The ability to produce butyrate and SCFAs is particularly interesting for restoring epithelial integrity, as their levels are linked to the increased expression of tight junction proteins such as occludin and claudins and the production of E-cadherin (50, 54). This may explain the clinical benefits observed in IBS-D patients treated with C. butyricum CBM588. Regarding Bifidobacteria, numerous strains have shown promising results in IBS management. Benefits include the regulation of μ-opioid and cannabinoid receptor expression, which contribute to reduced bloating, improved transit time and evacuation frequency, pain relief, better global symptom control in IBS-C, and improved quality of life (33, 47, 55). These findings are consistent with the results observed in our study with B. longum W11. Lastly, a final consideration should be made regarding the reduction in total IBS symptom scores. Both probiotic treatments resulted in statistically significant reductions (p < 0.01), and beyond statistical significance, meaningful clinical improvements were also observed. However, a more detailed assessment of symptom severity is essential. According to standard scoring criteria, severity is defined as follows: 75–174 = mild, 175–299 = moderate, and >300 = severe (56). Overall, the results of our study are in line with the existing literature on similar probiotic strains and support a more targeted use of specific microbial agents for managing distinct IBS variants. A key strength of this study lies in its innovative design, which addresses the two predominant subtypes of irritable bowel syndrome, IBS-D and IBS-C, through a targeted and differentiated probiotic intervention. By evaluating Clostridium butyricum CBM588 and Bifidobacterium longum W11 in patient groups stratified by symptom profile, the study adopts a precision approach that mirrors the growing need for individualized treatment strategies in functional gastrointestinal disorders. Unlike many previous investigations that consider IBS as a single, homogeneous entity, this study highlights how distinct pathophysiological mechanisms may respond to specific microbial strains. The age-related differences in symptom perception, the correlation between baseline symptom severity and treatment response, and the absence of significant side effects further enhance the study’s relevance. Overall, the findings support the idea that precision probiotic therapy represents a valuable addition to the therapeutic arsenal for IBS, offering a tailored, microbiota-targeted strategy that aligns with the broader evolution of personalized medicine in gastroenterology.

This study demonstrated that Clostridium butyricum CBM588 and Bifidobacterium longum W11 are effective in managing IBS-D and IBS-C, respectively, significantly improving symptom severity and quality of life without notable side effects. The results highlight a direct correlation between symptom severity and treatment efficacy, reinforcing the potential of targeted probiotic interventions in IBS management. The observed improvements, particularly in bloating and overall symptom scores, align with existing literature, supporting the rationale for strain-specific probiotic strategies, also to improve the impact of symptoms on quality of life at any age.