Assessing the maternal transfer of Lactobacilli to the intestine of CD‐1 murine fetuses.
Authors: Hashemi Ashkan , Johnson‐Henry Kathene , Taibi Amel , Stinson Sara E. , Tompkins Thomas , Sherman Philip M. , Comelli Elena M. 
Published: November 2023

RationaleRecent research suggests that the fetus is not sterile; Gram‐positive and Gram‐negative bacteria have been detected in the human placenta, umbilical cord and meconium. In addition, maternally administered probiotic Lactobacillus rhamnosus GG during weeks 30–36 of gestation has been recovered from the feces of offspring up to 24 months of age. Similarly, in mice, Enterococcus faecium has been found in the meconium of pups whose mothers received the bacterium during pregnancy. However, this area of research is still at its infancy and mechanisms underlying maternal transfer of microorganisms still need investigation.ObjectiveTo assess whether there is maternal transfer of lactobacilli to the fetus during gestation.Study Design & Methods6‐week old female CD‐1 Elite (specific pathogen free) mice were randomized to receive probiotic Lacidofil® (a mixture of L. rhamnosus R0011 and L. helveticus R0052 in a 95:5 ratio) (1×109 CFU/mL, P; n= 6) or nothing (control, C; n= 4) in their drinking water for 1 week prior to mating and throughout pregnancy. Dams were sacrificed at E19 (full gestation) and the umbilical cord, and fetal small and large intestine were collected. All procedures were conducted in a sterile facility; mice received sterile chow and water and were dissected in a biosafety cabinet. DNA from collected tissues was isolated and digital droplet PCR used to quantify total bacteria and lactobacilli while L. rhamnosus R0011 was analyzed by qPCR with strain‐specific primers.ResultsBody weight increased throughout pregnancy independently of probiotic administration, and litter size did not differ between groups (C, 12±0.41 fetuses; P, 11.83±0.54 fetuses; p= 0.83). Lactobacilli were found in all tissues studied with no difference in % lactobacilli (normalized to total bacteria) between control and probiotic‐treated dams in umbilical cord (C, 55.32 ± 10.70%; P, 46.00 ± 13.04%; p= 0. 0.6008), fetal small (C, 25.66 ± 6.528%; P, 27.62 ± 4.463%; p=0.8025) and large (C, 37.26 ± 2.781%; P, 38.88 ± 5.270%; p= 0.8214) intestine. However, the specific strain L. rhamnosus R0011 was detected in the large intestine of fetuses derived from 50% of the probiotic‐treated dams (2.06×105CFU/g – 8.55×108 CFU/g) but not in controls. Future studies will assess the microbiome of other tissues.ConclusionThese data suggest that Lactobacillus may be a predominant genus in the umbilical cord and fetal gut at term. The presence of Lactobacillus DNA in the fetal intestine supports the emerging concept of in utero microbial exposure and the role it may play in health. Future studies will assess the viability of these bacteria. Although there were differences in the outcomes for maternal transfer of probiotic L. rhamnosus R0011 to the fetuses, these preliminary results provide proof that vertical transfer of microorganisms occur during gestation and that this can be modified by diet.Support or Funding InformationFunding: ‐NSERC Discovery Grant to EMC. ‐Lallemand Health Solutions donation in support of research program to EMC ‐AH is the recipient of a NSERC Canada Graduate Scholarship for Master's (CGSM) ‐SES is the recipient of an Ontario Graduate Scholarship (OGS) ‐PMS is funded by the Canadian Institutes of Health Research (MOP‐89894 and IOP‐92890) ‐EMC holds the Lawson Family Chair in Microbiome Nutrition Research at the University of Toronto.