Within each species of bacteria there is a multitude of strains. Some strains within a given species are strong and resilient, with a demonstrated capacity to survive the trip through the upper GIT, interact with the immune system, and inhibit pathogenic bacteria, whereas other strains are weak and cannot even survive transit through the stomach or small intestine. This is an extremely important concept to know, as it means that just because one strain of bacteria in a given species has a proven action or characteristic, it does not mean that another strain will too, even if they are closely related. if you are currently taking probiotics, take a look at the back of your bottle and identify whether the exact strain is listed.
Strains of bacteria within the same species can have significantly different actions, properties and characteristics, as many of these characteristics are strain-specific qualities. As an example, Lactobacillus plantarum strain 299v has been shown to effectively reduce IBS symptoms, whereas administration of L. plantarum strain MF1298 may actually worsen IBS symptoms. To achieve desired therapeutic outcomes, it is vital to have the specific probiotic strains that have demonstrated the therapeutic qualities required. Strains of bacteria, even those within the same species, can have significantly different therapeutic actions, properties and characteristics.
A probiotic strain that works in one condition will not necessarily be effective for other conditions. One example is the capacity of Lactobacillus rhamnosus GG to effectively prevent antibiotic-associated side effects, but not urinary tract infections.
Unfortunately, the concept of strain specificity is not well known amongst clinicians or consumers. Sometimes this leads to misleading information provided to consumers from supplement manufacturers. For example, a study that utilized a specific strain such as L. rhamnosus strain HN001 will be quoted on their probiotic supplement that contains a strain of L. fermentum or another strain of L. rhamnosus as doing the same. Unless proven, one cannot assume that a given strain of L. rhamnosus, L. acidophilus, B. bifidum or any other species of lactic acid bacteria will survive transit through the upper GIT, let alone have specific therapeutic actions.
When treating specific disease conditions, due to the potential for substantial differences between strains, it is recommended to utilize those strains with demonstrated efficacy in that condition.