Probiotics: quality matters

Probiotics are bacteria with beneficial health effects. Their efficacy and safety have been evaluated positively by the Cochrane Collaboration for several indications such as acute infectious diarrhea [1]. However, the Cochrane Collaboration has also noted that individual preparations can differ and “more research is needed to guide the use of particular probiotic regimens”. As highlighted in two recent review articles [2, 3], the efficacy and safety of probiotic depends not only on the biological properties of specific bacterial species and their strains, but also on the compositional quality of the preparations and their ability to persist in the gut.

Pharmaceuticals licensed as drugs are subject to rigorous quality controls; this applies not only to small molecules and antibodies, but also to probiotics. However, less stringent regulations are generally applied to preparations categorized as dietary supplement or functional foods. A recent review [2] based on 38 evaluations of 31 marketed probiotic drugs found that in 37% (14/38) of the evaluations the included product contained microorganisms other than those listed in the label, with 18% (7/38) found with contaminants. Moreover, only 29 products declared expected amounts on their label, for which 48% (14/29) were found to have differing amounts of bacteria compared to their respective labels. In total, only 29% (9/31) of the drug products consistently satisfied all three criteria in all studies (Tab. 1). The most often tested preparation was a Bacillus clausii product (Enterogermina®) that was found to satisfy all three criteria consistently across five separate studies.

Tab. 1. Compliance with the label claims of probiotic drugs marketed worldwide with focus on microbial composition, amount of living cells and presence of contaminant microorganisms. Reproduced with permission from [2].

A key challenge to orally administered probiotics is that they must survive the passage through the hostile (highly acidic) environment of the stomach to reach the gut in sufficient numbers to become biologically active. This is illustrated by an experimental study in which the survival of several marketed probiotic preparations was tested in three different simulated conditions (two gastric and one intestinal juices) [4]. Among the 10 tested preparations, only three maintained the initial number of microorganisms in two distinct simulated gastric juices and only two in simulated intestinal juice The B. clausii product Enterogermina® was the only product which conserved its biological activity in all three tests (Fig. 1), which can be attributed to its spore-forming capabilities [4].

A recent systematic review has assessed the survival rate of orally administered probiotic bacteria during gastro-intestinal transit based on clinical studies with 17 studies of single strains and 13 studies of multi-strain products [3]. When the administered dose was higher than 1010 colony-forming units/day, the probiotic could be recovered from stool regardless of the strain used. This was independent of treatment duration.

The B. clausii product Enterogermina®, despite being studied only after a single administration and at a lower dosage (6 billion CFU [colony forming units] versus probiotics administered up to 100 billion CFU), was among the ones with the highest amount recovered [3]. Such a result appears to confirm in a clinical setting the results observed in the preclinical model [4] and suggests that spores are highly resistant to the harsh conditions of gastro-intestinal transit.

The authors in the end concluded that general dosage recommendations for probiotics by regulatory agencies are not high enough for a strain to survive, persist and be efficacious in the gut. Additionally, it was noted that resistance to gastro-intestinal transit is strain specific, with spore-forming bacteria among the ones with higher survivability and persistence. Of interest, among spore formers included in the study, B. clausii appears to have better ability to resist to the gastrointestinal tract [3].

We conclude that greater rigor is required in controlling the pharmaceutical quality of marketed probiotic products and that the same attention should be reserved to fully elucidate the ability of the strain to reach and persists and multiply in the intestine. Such a latter characteristic appears to be strain dependent and poorly affected by the matrix or by the dosage, especially when probiotics are administered in dosages lower that 10 billion CFU. The B. clausii product Enterogermina® appears to be one of the few preparations consistently fulfilling the required criteria on compositional quality, survivability and persistence.

_{Conflict of interest: P. Pellegrino and M. Perez III. are employees of Sanofi.}

_{Disclosures: Medical writing and publication funded by Sanofi.}