Perhaps the most studied site for investigating probiotic efficacy is the gastrointestinal tract (GIT) and inflammatory conditions such as Crohn’s disease (CD), ulcerative colitis (UC) and irritable bowel syndrome (IBS). Patients diagnosed with inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS) have been reported to present with increased pro-inflammatory or potentially pathogenic bacterial species such as Escherichia coli,1,2 members of the genus Bacteroides3 and Enterococci; and decreased Bifidobacteria and Lactobacilli species.4,5 For example, the etiology of IBD is not fully understood, but is considered to be a T-cell-driven inflammatory response resulting from a persistent preponderance of pro- anti-inflammatory cytokine production,6 whereas, Crohn's disease (CD) is reported to be driven by an T-helper 1 (TH1) immune response7,8 that can affect any part of the GIT, i.e., from the mouth to the anus. By contrast, UC is a T-helper 2 (Th2) driven response, and is restricted to the mucosa of the colon and rectum.8,9
Role of Probiotics in Gastrointestinal Conditions
It has been reported that probiotic bacteria may operate on three levels of host functionality via their metabolite production that enhances GIT and extra-intestinal activity namely by (a) interfering with the growth of pathogenic bacteria in the lumen of the GIT; (b) strengthening gut epithelial barrier function and mucosal immunity as well as mucus production; and (c) beyond the gut-brain, and heart. A series of clinical trials reviewed elsewhere10,11 that implemented various combinations of probiotic species frequently demonstrated efficacy in treating GIT conditions/diseases and various other end-organ tissues.10,11 The core notion emanating from the reviews was the administration of multi-species probiotic formulations could, in addition to improving GIT function, influence numerous end-organ tissues beneficially. Furthermore, clinical studies indicate that administration of probiotic bacterial species provides efficacious results in restoring the GIT microbiome to a more balanced metabolic state. This possibly achieved in part by reducing pathogenic bacterial overgrowth and the resulting adverse localized effects that in turn affect end-organ physiology.
Role of Probiotics in IBD
Probiotics have been shown to reduce abdominal pain, discomfort, and symptom scores in patients with IBS when administered Lactobacillus acidophilus,12 Lactobacillus plantarum,13 or ProSymbioflor (a combination of E. coli DSM and Enterococcus faecalis)14 compared with a placebo (see Table 1). In contrast, Drouault-Holowacz and colleagues15 found that Bifidobacterium longum, L. acidophilus, Lactobacillus lacti and Streptococcus thermophilus were not superior to the placebo treatment for relieving disease symptoms except that of abdominal pain, due to a strong placebo effect. Further analysis of the IBS subgroups revealed that patients with changing bowel habits (alternating between constipation and diarrhea and those with short durations of symptom exacerbation and remission) reported significantly less abdominal pain with constipation-predominant IBS patients reporting improved bowel motions. These results indicate that different disease etiologies may exist between IBS subgroups and that some probiotics may be more efficient than others for treating symptoms within these subgroups. These findings also point to the need to further classify patients into relevant sub groups whenever possible for assessing the efficacy of a probiotic.
Table 1. Role of probiotics in human clinical studies on GIT disorders.
A number of studies investigating the effects of probiotics within specific sub-groups of IBS have shown the beneficial effects of probiotic supplements. Therefore, Zeng and colleagues16 first separated patients with IBS into sub groups (those with increased small bowel permeability and those with increased colonic permeability), treating diarrhea-predominant IBS patients with S. thermophilus and Lactobacillus bulgaricus, Lactobacillus bulgaricus and B. longum. The proportion of patients with increased small bowel permeability (lactulose/mannitol ratio >0.025) decreased significantly (p < 0.023) after treatment. These patients also demonstrated improved IBS scores with diminished abdominal pain and flatulence. Similarly, symptoms improved after treatment with the probiotic VSL#3 in subjects with either diarrhea-predominant IBS17 or IBS with bloating.18 In subjects complaining of IBS with bloating, the VSL#3 reduced flatulence scores and retarded colonic transit time, without altering bowel function. In patients with diarrhea-predominant IBS, VSL#3 only relieved abdominal bloating, having no effect on mean transit measures, bowel function scores or satisfactory relief of symptoms. VSL#3 has also been shown to be superior to a placebo in children with IBS. VSL#3 supplementation improved overall IBS symptoms as assessed by abdominal pain/discomfort, abdominal bloating/gassiness, and on family life disruption.
It is therefore evident, that a multi-species probiotic consisting of multiple species from the genera of Lactobacillus, Bifidobacteria, Streptococcus and Saccharomyces demonstrates numerous therapeutic effects in relieving symptomologies associated with IBS and UC, with limited evidence for their use in CD.
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