Not all bacteria are created alike.
I’ve written about this issue previously, but it bears repeating, as so many people stumble in their health efforts because of it. It’s the issue of strain specificity when it comes to bacteria.
To illustrate, my favorite example is E. coli. You have E. coli, your family members have E. coli, neighbors and coworkers have E. coli. It is a common commensal species, i.e., a harmless species harbored in your gut. There are even species such as E. coli Nissle 1917 that yield substantial beneficial effects such as protection against ulcerative colitis and diverticular disease. But consume Romaine lettuce contaminated by so-called enteropathogenic strains of E. coli due to contamination from cow manure and you can develop intractable diarrhea, dehydration, kidney failure and death—same species, E. coli, different strain.
Lactobacillus rhamnosus provides another example. L. rhamnosus GG strain accelerates recovery from diarrhea that typically follows a course of antibiotics taken for, say, a urinary tract infection. This strain can also provide protection against infections, such as intestinal infection caused by Salmonella, a common source of food poisoning. Most other strains of L. rhamnosus, however, fail to provide these benefits. Take a look at the commercial probiotic you purchased (for a lot of money) that contains L. rhamnosus—is a strain specified? More than likely, no strain is specified.
Typically, strains that have an abundance of research validating their effects come with a higher price tag from the manufacturer. Probiotic retailers who purchase microbes from manufacturers often ignore issues of efficacy and opt instead to include lower cost strains. A strain with proven efficacy may cost, for instance, $700 per kilogram, while a strain without proven efficacy—or no efficacy at all for a specific condition—might cost something like $120 per kilogram. Probiotic retailers that sell products that list 10, 12, or more species usually purchase microbes based on price, not on efficacy. It therefore means that the probiotic you purchased to accelerate relief from diarrhea after taking an antibiotic may include L. rhamnosus but, without specifying the strain, it likely does not provide this benefit.
The same issue applies to more serious situations. One of the feared complications of taking an antibiotic is proliferation of Clostridium difficile that causes painful bloody diarrhea, even death. There are strains of L. rhamnosus and other species that have been shown to reduce the likelihood of C. diff infection. But, once again, buy a commercial probiotic that contains L. rhamnosus with no strain specified and you likely do not obtain protection against this feared complication.
Admittedly, this creates a real tangle in knowing which strains work and which do not. With our L. reuteri yogurt, for example, we know that the DSM 17938 and ATCC PTA 6475 strains increase oxytocin release from the pituitary gland and thereby yield effects such as smoother skin, reduced skin wrinkles, accelerated healing, increased feelings of empathy, restoration of youthful muscle and other benefits. Take another commercial strain of L. reuteri and maybe you experience these effects, maybe you don’t. (We are planning several studies to explore these strain-specific issues with L. reuteri.) It is therefore best to go with strains that you know yield the benefits you desire, rather than roll the dice in the hopes that the strain you have does the job.
For these reasons, whenever I discuss this or that microbe, you will see that I specify strains, else the discussion is useless. This is not to say that probiotics or fermented foods without known strains yield no benefit—they do provide modest benefits such as discouraging proliferation of various pathogens, increased production of healthy metabolites such as butyrate or vitamin B12, and encouraging intestinal mucus production. But if you are seeking specific benefits such as protection against C. diff, increased dermal collagen, or reduced muscle injury during strenuous exercise, then attention to strain is crucial.