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Reprod Sci. 2019 Aug;26(8):1045-1053. doi: 10.1177/1933719118804411. Epub 2018 Oct 11.

Antenatal Microbial Colonization of Mammalian Gut.

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1 Dipartimento di Scienze della Salute, Università degli Studi di Milano, Milan, Italy.
2 Institute of Biomedical Technologies, National Research Council, Milan, Italy.
3 Centro Ricerca Tettamanti, Clinica Pediatrica, Dipartimento di Medicina e Chirurgia, Università degli Studi di Milano-Bicocca, Fondazione MBBM, Monza, Italy.
4 Dipartimento di Scienze e Politiche Ambientali, Università degli Studi di Milano, Milan, Italy.


The widely accepted dogma of intrauterine sterility and initial colonization of the newborn during birth has been blurred by recent observations of microbial presence in meconium, placenta, and amniotic fluid. Given the importance of a maternal-derived in utero infant seeding, it is crucial to exclude potential environmental or procedural contaminations and to assess fetal colonization before parturition. To this end, we analyzed sterilely collected intestinal tissues, placenta, and amniotic fluid from rodent fetuses and tissues from autoptic human fetuses. Total bacterial DNA was extracted from collected samples and analyzed by Next Generation Sequencing (NGS) techniques using hypervariable 16S ribosomal RNA (rRNA) regions (V3-V4). Colonizing microbes were visualized in situ, using labeled probes targeting 16S ribosomal DNA by fluorescent in situ hybridization. The NGS analysis showed the presence of pioneer microbes in both rat and human intestines as well as in rodent placentas and amniotic fluids. Microbial communities showed fetus- and dam-dependent clustering, confirming the high interindividual variability of commensal microbiota even in the antenatal period. Fluorescent in situ hybridization analysis confirmed the microbes' presence in the lumen of the developing gut. These findings suggest a possible antenatal colonization of the developing mammalian gut.


16S rRNA gene sequencing; embryonic development; mammalian gut; microbiota

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