Probiotics Just Passing Through

Twenty years ago, the conventional wisdom was that colonization is a requirement for probiotics. In vitro cell culture assays were considered evidence of colonization. Once human feeding trials were conducted, strain-specific assays showed that probiotics were recovered at most for a couple of weeks from feces of adults who consumed the probiotic. This was true even for strains with robust ability to colonize in cell culture assays. This pattern was found for different strains of Lactobacillus species, Bifidobacterium species, Bacillus coagulans and Saccharomyces boulardii.  Today, probiotics are considered to be transient colonizers, although longer-term colonization has been reported on rare occasions.

A recent paper by Dotterud et al. (2015) looks at the issue of probiotic colonization from a different angle.  The authors examined if maternal perinatal probiotic supplementation altered the intestinal microbiota of the mother or the child and if probiotic strains could be identified in fecal samples. This study is important because it addresses if probiotics might colonize more permanently if they are being administered to the naïve, sparsely colonized gut of the infant through maternal exposure. If they are introduced to the pregnant mother, would microbial transfer through the placenta, through breast milk or direct transfer through maternal:infant contact enable the probiotic to permanently colonize?

To address this question, Dotterud et al. randomized 415 pregnant women to a double-blind trial. From 36 weeks gestation through 3 months postnatally, they received either sterile milk or milk containing 5×1010 cfu Lactobacillus rhamnosus GG, 5×1010 cfu Bifidobacterium animalis subsp. lactis Bb-12 and 5×109 cfu Lactobacillus acidophilus La-5. The microbiota of feces from both the mother and infant were analyzed.

The probiotic strains were found during probiotic feeding in the mothers, but only one of the probiotic strains, Lactobacillus rhamnosus GG, was found in the infants – at 10 days and 3 months of age. However, probiotic strains were not recovered from the infants at 1 or 2 years of age.

This study demonstrates that colonization ability differs among different strains and is not permanent, even when exposure occurs prenatally to the naïve gut. The study also confirms that the probiotic can be transferred maternally to the infant. One confounder of this study is that La-5 was administered at a 10-fold lower dose than the other 2 strains, so the failure of La-5 to be recovered may be due to strain-specific or dose-specific factors. Finally, the study reinforces findings of other studies (see Probiotics impact gut microbiota: not what’s there but what they are doing) that administration of traditional probiotics do not alter microbial composition.


Dotterud CK, Storrø O, Johnsen R, Oien T.  Probiotics in pregnant women to prevent allergic disease: a randomized, double-blind trial.  Br J Dermatol. 2010 Sep;163(3):616-23

Dotterud CK, Avershina E, Sekelja M, Simpson MR, Rudi K, Storrø O, Johnsen R, Øien T. Does Maternal Perinatal Probiotic Supplementation Alter the Intestinal Microbiota of Mother and Child? J Pediatr Gastroenterol Nutr. 2015 Aug;61(2):200-7. doi: 10.1097/MPG.0000000000000781.