General:

Mother-to-Infant Microbial Transmission from Different Body Sites Shapes the Developing Infant Gut Microbiome (2018): https://www.cell.com/cell-host-microbe/fulltext/S1931-3128(18)30317-2 Maternal skin and vaginal strains colonize only transiently, and the infant continues to acquire microbes from distinct maternal sources after birth. Maternal gut strains proved more persistent in the infant gut and ecologically better adapted than those acquired from other sources. The maternal gut microbiome is the source of the majority of transmitted strains.

Strain-Level Analysis of Mother-to-Child Bacterial Transmission during the First Few Months of Life (2018): https://www.cell.com/cell-host-microbe/fulltext/S1931-3128(18)30319-6 Varying inheritance, likely driven by functional selection.

Selective maternal seeding and environment shape the human gut microbiome (2018): https://genome.cshlp.org/content/early/2018/03/14/gr.233940.117.abstract "we show strong evidence of selective and persistent transmission of maternal strain populations to the vaginally born infant and their occasional replacement by strains from the environment, including those from family members, in later childhood. Thus, the infant gut is seeded by selected maternal bacteria, which expand to form a stable community, with a rare but stable continuing strain influx over time"

Differences in the fecal microbiota of neonates born at home or in the hospital (2018): https://doi.org/10.1038/s41598-018-33995-7

Does the maternal vaginal microbiota play a role in seeding the microbiota of neonatal gut and nose? (2017) http://www.wageningenacademic.com/doi/10.3920/BM2017.0064 "The sources of a large proportion of infant microbiota could not be identified in maternal microbiota, and the sources of seeding of infant gut and nasal microbiota remain to be elucidated."

Only 30% of the gut microbiome is seeded from breast milk (July 2017): https://jamanetwork.com/journals/jamapediatrics/article-abstract/2625334

Study of human milk functional activity vs actual breastfeeding (latching). Infants unable to actively suck were fed mother's milk. Feeding directly from the breast can contribute to the preterm infant’s microbiome assembly, in addition to the intrinsic health-promoting effects of milk itself. The milk microbiome composition seemed to change following the infant’s latching to the mother’s breast, shifting toward a more diverse microbial community https://doi.org/10.3389/fmicb.2018.02512. Microbial Community Dynamics in Mother’s Milk and Infant’s Mouth and Gut in Moderately Preterm Infants (2018). Additional supporting studies.

A prokaryotic viral sequence is expressed and conserved in mammalian brain (2017): http://www.pnas.org/content/114/27/7118

Review, 2015: On the origin of species: Factors shaping the establishment of infant's gut microbiota: http://onlinelibrary.wiley.com/doi/10.1002/bdrc.21113/full

vaginal birth did not result in infant mycobiomes that were more similar to the mother’s vaginal mycobiome. Therefore, although vertical transmission of specific fungal isolates from mother to infant has been reported, it is likely that other sources (environment, other caregivers) also contribute to early-life mycobiome establishment (2018): http://msystems.asm.org/content/3/3/e00140-17

Bifidobacteria isolated from vaginal and gut microbiomes are indistinguishable by comparative genomics (2018): http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0196290 "results of this study support the hypothesis that the vaginal and gut microbiomes are colonized by a shared community of Bifidobacterium, and further emphasize the potential importance of the maternal vaginal microbiome as a source of infant gut microbiota"

The influence of maternal vaginal flora on the intestinal colonization in newborns and 3-month-old infants (2018): https://doi.org/10.1080/14767058.2017.1319352 "Vaginal flora is a potent factor influencing the development of bacterial flora in the neonatal and infantile gut"

Preterm infants have distinct microbiomes not explained by mode of delivery, breastfeeding duration or antibiotic exposure (2018): https://academic.oup.com/ije/advance-article-abstract/doi/10.1093/ije/dyy064/4980972

Strain-specific DNA analysis has shown that at least some of the microbiota can be maintained across hundreds of thousands of host generations (2018): https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-018-0457-9

Analysis of 1,174 time-series metagenomes from 161 premature infants revealed fungal colonization of 13 infants, primarily in the first two weeks of life. Nearly all 24 NICU samples contained eukaryotes, and the most diverse communities were in NICU sinks. highlighting the potential of hospital-associated fungi to colonize hospitalized infants (2018): https://www.biorxiv.org/content/early/2018/05/17/324566

Shared and Distinct Features of Human Milk and Infant Stool Viromes (2018): https://www.frontiersin.org/articles/10.3389/fmicb.2018.01162/full - "viral communities were mostly distinguishable between milk and infant stool, but each was quite distinct from adult stool, urine, and salivary viromes. There were significant differences in viral families in the infant stool (abundant bacteriophages from the family Siphoviridae) compared to milk (abundant bacteriophages from the family Myoviridae), which may reflect significant differences in the bacterial families identified from both sites. Despite the differences in viral taxonomy, we identified a significant number of shared viruses in the milk and stool from all mother-infant pairs"

Neonatal selection by Toll-like receptor 5 influences long-term gut microbiota composition (2018): https://www.nature.com/articles/s41586-018-0395-5 | News article on this study: https://www.nature.com/articles/d41586-018-05861-z

Early-life exposure to gut microbiota from disease protected mice does not impact disease outcome in type 1 diabetes susceptible NOD mice (2018): https://doi.org/10.1111/imcb.12201

Researchers found that differences in the first microorganisms that arrive in the gut after birth, and their order of arrival, have a lasting impact on how gastrointestinal system looks later in life. https://www.upi.com/Health_News/2018/09/18/First-gut-bacteria-may-affect-future-ability-to-fight-chronic-diseases/6661537289989/ Experimental evaluation of the importance of colonization history in early-life gut microbiota assembly https://doi.org/10.7554/eLife.36521

Mouse Microbiomes Are Mostly Inherited. Transmission modes of the mammalian gut microbiota (Oct 2018). The microbiota of the two mouse lineages remained distinct even after 10 generations. Most microbiota genera transmitted vertically. Those taxa that transmitted horizontally through the shared environment of the animal facility tended to be those that include pathogens. https://www.the-scientist.com/news-opinion/mouse-microbiomes-are-mostly-inherited-64998

Neonatal gut and respiratory microbiota: coordinated development through time and space (2018): https://doi.org/10.1186/s40168-018-0566-5 "community state types of any one body site was highly predictive of the CSTs at other body sites. Findings suggest that early microbiota is shaped by neonatal innate and adaptive developmental responses"

"breastfeeding duration in early life and pre-school dietary lifestyle correlated with the composition and functional competences of the gut microbiota in the children at school age (6–9 years of age). Our work highlights the persistent effects of breastfeeding duration and pre-school dietary lifestyle". Impact of early events and lifestyle on the gut microbiota and metabolic phenotypes in young school-age children (2019): https://doi.org/10.1186/s40168-018-0608-z

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Fish:

"the dominant taxa residing in the gut do not share their niche habitats with the abundant microbiota in the surrounding environment [...], complex gut microbiota could not be simple reflections of environmental microbiota. We further conclude that microbial changes in ontogenesis can be independent of the effects of dietary shifts " (2018): https://www.frontiersin.org/articles/10.3389/fmicb.2018.00495/full

Diet and other environmental factors shape the bacterial communities of fish gut in an eutrophic lake (2018): https://onlinelibrary.wiley.com/doi/abs/10.1111/jam.14064 "fish harbored specific groups of bacteria that do not completely reflect the microbiota of the environment or prey"

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Drosophila:

Researchers at Umeå university in Sweden have published a new study showing that the gut bacteria can carry information of past experiences of an altered environment from parents to offspring. Eggs and sperm are not the only information carriers from one generation to the next. "The gut microbiome participates in transgenerational inheritance of low temperature responses in Drosophila melanogaster (2018)" https://phys.org/news/2018-11-parents-guts-tales-children.html - http://dx.doi.org/10.1002/1873-3468.13278

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Placental microbiome:

Article: Could baby’s first bacteria take root before birth? The womb was thought to be sterile, but some scientists argue that it’s where the microbiome begins. (2018): https://www.nature.com/articles/d41586-018-00664-8

Microbiome in normal and pathological pregnancies: A literature overview (2018): https://onlinelibrary.wiley.com/doi/abs/10.1111/aji.12993 "We present data suggesting that, contrary to traditional understanding, the placenta is not sterile but has a microbial community. Several factors influence the bacterial profile of these women and may explain, at least in part, some of the discrepant findings between studies. Many factors, including genetics, BMI, ethnicity, diet, the use of antibiotics, and environmental conditions, may influence the bacterial profile of pregnant women and help explain some discrepancies in results."

Commentary: Uterine Microbiota: Residents, Tourists, or Invaders? (2018): https://doi.org/10.3389/fimmu.2018.01874 - includes semen as a transmitter of microbes.

Initial microbial community of the neonatal stomach immediately after birth (2018): https://www.tandfonline.com/doi/full/10.1080/19490976.2018.1520578 "Total microbial content was low in many samples, with a substantial number sharing taxonomic composition with negative controls. qPCR targeting the 16S rRNA gene showed that infants delivered vaginally had a higher microbial load than infants delivered by C-section. Samples from many infants had low microbial load near the edge of the detection limit."

Review, 2018: Uterine microbiome—low biomass and high expectations https://doi.org/10.1093/biolre/ioy257

For:

Review, 2018: The Prenatal Microbiome: A New Player for Human Health https://www.mdpi.com/2571-5135/7/4/38/htm

Characterisation of the bacterial microbiome in first-pass meconium using propidium monoazide (PMA) to exclude non-viable bacterial DNA (2019): https://doi.org/10.1111/lam.13119 "Our findings suggest that the fetal gut is seeded with intact bacterial cells prior to birth. This is an important finding, as exposure to live bacteria during gestation might have a significant impact on the developing fetus"

Bacterial DNA is present in the fetal intestine and overlaps with that in the placenta in mice (2018). http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0197439

Conclusion: The female upper genital tract is not sterile. Distinct microbial community profiles in the fallopian tubes of healthy women suggest that this genital tract site supports an endogenous microbiota. (2018): http://www.oncotarget.com/index.php?journal=oncotarget&page=article&op=view&path%5B%5D=25059

Microbiome in normal and pathological pregnancies: A literature overview (2018): https://onlinelibrary.wiley.com/doi/abs/10.1111/aji.12993 "We present data suggesting that, contrary to traditional understanding, the placenta is not sterile but has a microbial community. Several factors influence the bacterial profile of these women and may explain, at least in part, some of the discrepant findings between studies. Many factors, including genetics, BMI, ethnicity, diet, the use of antibiotics, and environmental conditions, may influence the bacterial profile of pregnant women and help explain some discrepancies in results."

Seeding of the Fetal Gut Microbiome: Insights Into Origins and Significance (2018): https://onlinelibrary.wiley.com/doi/full/10.1111/jpc.13882_7 "All meconium samples contained detectable levels of bacterial DNA and the immunomodulatory SCFAs acetate and propionate, confirming the hypothesis that the fetal gut is inoculated with bacteria in utero. Seeding of the fetal gut microbiome commences prenatally and may originate from the endometrial microbiome present at time of conception; vaginal contribution appears minimal"

HPV infection and bacterial microbiota in the placenta, uterine cervix and oral mucosa (2018): https://www.nature.com/articles/s41598-018-27980-3#Sec7 - "Our data may be interpreted to corroborate the hypothesis of a distinct microbiota of placenta"

Maternal influence on the fetal microbiome in a population-based study of the first-pass meconium (2018): https://sci-hub.tw/https://www.nature.com/articles/pr201829 "The microbiome of the first-pass meconium was not altered by immediate perinatal factors but was affected by maternal factors during pregnancy implying the in utero transfer of microbes and the development of the gut microbiota niche in fetal life"

Comparison of Meconium DNA Extraction Methods for Use in Microbiome Studies (2018): https://www.frontiersin.org/articles/10.3389/fmicb.2018.00270/full

Streptococcus mutans in Umbilical Cord Blood, Peripheral Blood, and Saliva from Healthy Mothers (2018): https://link.springer.com/article/10.1007/s00284-018-1532-y

Fallopian tube microbiota: evidence beyond DNA (2018): https://doi.org/10.2217/fmb-2018-0118 "In the absence of inflammatory pathology, the fallopian tube harbors a visually observable microbial population, which correlates with cultivation-dependent and -independent data, further refuting the sterility of this anatomical niche"

"The intestinal tract of an unborn is, despite general belief, not sterile, but contains bacteria that have been transferred from the mother." (Review, Oct 2017): http://www.wageningenacademic.com/doi/10.3920/BM2017.0066 - https://sci-hub.cc/http://www.wageningenacademic.com/doi/10.3920/BM2017.0066

Microbial communities in placentas from term normal pregnancy exhibit spatially variable profiles. Yet another study showing a placental microbiome (Sept 2017). https://archive.is/W17tE

Contributions of the maternal oral and gut microbiome to placental microbial colonization in overweight and obese pregnant women (June 2017): https://www.nature.com/articles/s41598-017-03066-4

These data showed that BCG L-forms have the capacity to pass trans-placental barrier and that maternal BCG vaccination affects the placentobiome (2017): https://www.nature.com/articles/s41598-017-17644-z

A 2014 article on this topic: https://www.newscientist.com/article/dn25603-babys-first-gut-bacteria-may-come-from-mums-mouth/

Bacteria Found in Women’s Upper Reproductive Tracts. A new study identifies microorganisms residing in the human fallopian tubes and uterus, but some researchers are skeptical of the findings. 2017: http://www.the-scientist.com/?articles.view/articleNo/50665/title/Bacteria-Found-in-Women-s-Upper-Reproductive-Tracts/

Microorganisms in the human placenta are associated with altered CpG methylation of immune and inflammation-related genes (2017): http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0188664

The same thing was thought about breast milk: https://www.ncbi.nlm.nih.gov/pubmed/22974824

Phage passing the gut barrier when bacteria can't: https://www.theatlantic.com/science/archive/2017/12/we-might-absorb-billions-of-viruses-every-day/547415/

Zika virus crosses into the amniotic fluid: http://www.miamiherald.com/news/health-care/article209671964.html

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Against:

We conclude that for this sample set, using the methods described, we could not distinguish between placental samples and contamination introduced during DNA purification. (April 2016): https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-016-0172-3

A critical assessment of the “sterile womb” and “in utero colonization” hypotheses: implications for research on the pioneer infant microbiome. Conclusion: evidence is weak. (April 2017): https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-017-0268-4

Amniotic fluid from healthy term pregnancies does not harbor a detectable microbial community (2018): https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-018-0475-7 "bacterial microbiota of amniotic fluid was indistinguishable from contamination controls. Viral reads were sparse in the amniotic fluid, and we found no evidence of a core viral community across samples"

Lack of detection of a human placenta microbiome in samples from preterm and term deliveries (2018): https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-018-0575-4

Variations in placental microbiota appear related to premature birth. Enrichment of clinically relevant organisms in spontaneous preterm delivered placenta and reagent contamination across all clinical groups in a large UK pregnancy cohort (2018): http://aem.asm.org/content/early/2018/04/30/AEM.00483-18 - https://www.sciencedaily.com/releases/2018/05/180518133622.htm "analyses of overall community structure did not reveal convincing evidence for the existence of a reproducible ‘preterm placental microbiome’"

Is amniotic fluid of women with uncomplicated term pregnancies free of bacteria? (2018): https://www.ajog.org/article/S0002-9378(18)30438-1/fulltext

Bacterial communities found in placental tissues are associated with severe chorioamnionitis and adverse birth outcomes (2017): http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0180167