I find the word probiotic to be inherently problematic. It includes any and all microorganisms that have a single positive health benefit, whether or not they're detrimental in other regards. That if a bacteria were to penerate gut epithelium (very bad), it would still be a probiotic if it reduced constupation.

Even if the research supporting the health benefits of a supplemental bacteria is sound, a single study always has a restricted scope.

It's saddening that 'probiotics' have found their way to products such as baby formula, while there is pretty much no regulation governing their sales and use (at least in Europe).