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Compared with placebo, a heat-inactivated form of the probiotic Bifidobacterium bifidum MIMBb75 was associated with almost twice the reduction in abdominal pain, as well as significant relief of irritable bowel syndrome (IBS) symptoms during at least 50% of the treatment period, researchers reported.

Those receiving the inactivated probiotic had greater relief of individual IBS symptoms such as abdominal pain, distension and bloating, discomfort, painful bowel movements, and frequency of bowel movements, said Peter Layer, MD, of Israelitic Hospital in Hamburg, and colleagues.

In addition, as shown in their study online in several important parameters of treatment success showed significant improvement over placebo, including health-­related quality of life, IBS symptom scores, and global symptom relief.

"Because of these promising results, we expect more research will be done to understand the applications of non-viable bacterial strains in IBS and potentially in other gastroenterological diseases," the researchers wrote.

They noted that previous studies have found that the viable strain of B. bifidum, MIMBb75, IBS and its symptoms, but it was unclear whether the same would be true for the non-viable strain. Although generally safe, viable probiotic strains have been tied to infections and even septic complications in severely ill or immunocompromised patients.

"Therefore, non-viable bacterial strains could be a safe alternative and have further advantages over viable bacteria with regard to product stability and standardization, which could be particularly relevant for patients who are travelling or who are living in warm and humid climate zones," the researchers wrote.

They said the new results are the first to show that some beneficial bacterial effects may be mediated independent of cell viability, with the strong adhesive properties of viable B. bifidum to epithelial cells found to be preserved, and even increased, in the non-­viable form.

Study Details

The study participants were enrolled at 20 primary care and referral centers in Germany during 2016 and 2017; most patients were in their early 40s, and about 70% were women. IBS-diarrhea was the predominant form of the disease, affecting approximately 40% of the 443 participants overall, of whom 221 were assigned in double-blind fashion to active treatment and 222 to placebo. Patients recorded their pain levels and other IBS parameters daily. Median follow-up was 71 days.

The composite primary endpoint was reached by 74 of 221 patients (34%) in the probiotic group compared with 43 of 222 (19%) in the placebo group, for a risk ratio of 1.7 (95% CI 1.3-2.4, P=0.0007). A significantly greater proportion of patients in the probiotic arm (60%) reported adequate symptom relief, defined as a Likert score of 3 or less, than in the placebo group (44%).

No serious adverse events occurred in the active treatment group; there were seven adverse events suspected to be tied to the study product and eight in the placebo group, and no deaths were reported in either group. The most common reported adverse event was abdominal pain -- two patients in the treatment group and one in the placebo group (both representing less than 1% of the groups). Tolerability was rated as very good or good by 200 patients in the probiotic group (91%) versus 191 in the placebo group (86%).

In an , Nicholas J. Talley, MD, and colleagues, all from Newcastle University in New South Wales, Australia, said the results were of particular interest, especially since the investigators had examined the effect on all subtypes of IBS.

"The concept that a probiotic might be efficacious in IBS even if non-viable organisms are administered is an important observation," Talley and co-authors wrote. "However, the benefit over placebo of the probiotic used, B. bifidum HI-MIMBb75, was not as impressive as has been recently reported with fecal microbial transfer in IBS, suggesting that optimization of orally ingested bacterial therapy for IBS remains elusive."

In addition, the commentators explained, bacterial therapy does not appear to permanently change the patient's microbiome, with an effect seeming to depend on repeat administration and therapy cessation resulting in rapid cessation of relief. "The absence of fundamental knowledge in terms of how bacterial therapy alters mechanisms in IBS continues to hamper improvements in treatment, limiting any success to short-term symptom control rather than the true goal, reversal of disease," Talley and co-authors wrote.

A potential study limitation, they said, was the considerable placebo response, with a primary endpoint response rate of 19%.

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