I have written frequently about probiotics,(1,2) and the health effects of microorganisms seems a promising area of research. The current evidence for meaningful beneficial effects, however, is quite limited. There is reasonable evidence for some benefit in treating antibiotic-associated diarrhea or acute diarrhea of unknown cause(3). The evidence is not very good for many other claimed benefits, such as strengthening of immune system function, treatment of kidney disease(4,5), management of feline upper respiratory viral infections(6), and so on. And there are serious problems with irresponsible, excessive hype(7) and poor quality control(8) for probiotics.
One product I have written about, and used in my own patients, is Prostora from the Iams company. This product is attractive in several ways. It has good quality control and some supportive clinical trial evidence. However, I recently ran across an evaluation of the product produced in 2012 by the European Food Safety Authority (EFSA), which rejected the company’s application for approval to market Prostora in the European Union.
In terms of the efficacy of the product, the EFSA concluded that it could not reach a definitive judgment. According to the report, eight research studies were submitted in support of efficacy. Five of these were rejected for inadequate methodology (lack of a control group, for example). The three evaluated (including one I have reviewed here) did show some evidence of a beneficial effect. However, the effects were inconsistent and not always strong enough to be meaningful even if statistically significant.
More interesting to me was the concern raised in the report about the issue of antibiotic resistance. Apparently, the organism in Prostora has shown some resistance to the antibiotic clindamycin. A number of genes that confer antibiotic resistance have been identified, and some of these can be transmitted from one bacterium to another. The specific source of the resistance to clindamycin seen in the Prostora bacterium is not known, so it is not clear if this resistance could be transmitted to other bacteria in animals or people exposed to Prostora.
Because of this uncertainty, and the serious and growing problem of antibiotic resistance in infectious organisms, the EFSA chose not to approve the sale of Prostora in the EU. It has been approved here in the U.S. under the much less strict laws governing dietary supplements.
The EFSA in general has taken a conservative stance on probiotics, which some argue is appropriate based on the currently available evidence, and which others, notably probiotic manufacturers, have claimed ignores relevant science. There is some scientific evidence indicating that antibiotic resistance can be exacerbated by the use of probiotic organisms with such resistance, though the extent of the risk is not well-documented.
As I have often said about probiotics, because they clearly have the ability to affect the health of people and animals, they undoubtedly have risks as well as benefits. The devil is in the details, and they should neither be rejected out of hand nor embraced unquestioningly as beneficial. The specific risks and benefits of particular organisms for particular health conditions in particular species have to be understood through the careful and laborious process of scientific research. There is nothing intrinsically “alternative” about the use of microorganisms to affect health, but the indiscriminate use of them in the absence of appropriate scientific evaluation would be a mistake in the tradition of the worst kind of alternative medicine.