Placenta Discussion

Placenta has microbial communities with low biomass. We can found its composition with the help of DNA based techniques. In the term deliveries from the healthy women has high amount of Propionibacterium and Lactobacillus in their placenta.  In pre term cases, Lactobacillus bacteria are present in less amount. It shows its role as a commensal or positive bacteria in pregnancy.

Pre-term birth:

It is very difficult to found the exact mechanism which is involved in sudden preterm birth. Now we recognized that a preterm birth is due to an inflammatory response linked with mother immune system or infection caused by a bacteria or it may be colonizes in the fetus tissue leads to preterm birth. Birth becomes fast due to these facts. We have many proofs that shows that preterm delivery is caused by bacteria, that bacteria is very different from the bacteria in term delivery. In many cases the bacteria follows the ascending route for infection which is from vagina to cervical canal. These bacteria’s are similar to the bacteria which causes chorioamnionitis, a disease in which tissues of chorion and amnion are get inflamed.  It causes early delivery.

Pre term birth cases has placental microflora which is also differed according to the acerbity of chorionamnionitis. With the help of metagenomics analysis we have to know about some very definite metabolic reactions of bacteria in case of chorioamnionitis and also in normal condition which hypothesized as a cause for pre term birth. In a study, different roles are assigned to cohorts which based on histologic chorioamnionitis and gestational age. An increased number of inflammatory cytokines of cord blood was present in cases with severe funisitis and chorioamnionitis. As the chorioamnionitis becomes severe placental membrane microbial flora was altered too. In the literature, they found both oral commensals and urogenital bacteria in chorioamnionitis which followed to preterm birth. Placenta are colonized by bacteria just not in preterm and cases with chorioamnionitis but in normal deliveries and term birth too. In term and pre term birth they found that Gram negative and gram positive bacteria are colonize the 3rd of all the placentas. Interestingly, these bacteria are interacellular, present in cells of extravillous trophoblast in the decidua of mother. Mother immune and stromal cells are in direct contact with extravillous trophoblast, these are derived by fetus. Extravillous trophoblast has very different immunity advantage just because of its covering with self-antigens. Its include HLA-G, MAJOR antigen for histocompatibility, which is very important for the immunity of fetus.

Another study gives proofs for bacterial colonization in the placenta. They also identified a less abundant microflora which is very rich in metabolic activities. Method which are used for analysis was whole genome shotgun method based on DNA genome. They analysed samples of placenta in term and preterm deliveries. They identified some bacteria which are classified as commensals includes, Neisserialactamica,Bacteriodes species, Escherichia coli, Fusobacterium and Prevotella tannerae species.Escherichia coli was present in huge amount in placental samples. Before 28th weeks of period of gestation, placentas having intracellular microflora increased by half. When this study is compared with microflora of placenta in preterm and term, they came to know that placentas with pre term have abundance of bacteria Burkholderia species and in case of term paenibacilli bacteria was in abundance. Above mentioned extravillous trophoblast cells are known as sites for pathogen entry. These pathogens includes Toxoplasma gondii, Escherichia coli and Listeria monocytogenes. Extravillous trophoblast cells which are placed at basal plate of mother may work as protection for microbes of placenta. Placenta having microflora is not so surprising because it is primary organ used for nourishment and feed for the fetus. (1, 6, 7)


Term birth:

A study is designed for the determination of microbiota whether it exists in the placentas of term cases. Cesarean section which is without labor is analyzed asnormal term case. Different microbiological techniques was used for analysis includes, metagenomics, qPCR, cultivation and 16S rRNA gene sequencing. In this study, resident microbial community was not identified from the placentas which are delivered in cases of term without any labor. When background is controlled technically then placenta did not contains any microbial DNA. They cannot found any difference in structure and composition of bacteria which is present in technical control and placenta. In their study 28 cultures are negative out of 29 cultures.  When they analyzed placenta through metagenomics then find some sequences of bacteria from plant pathogens, aquatic bacteria, and cynobacteria. These bacteria are unlike human microbial communities so these are not considered. The basic find of this study is that the placenta of term patient without labor did not have microbiota. (2)


Placenta is not explored so much and it is unsure to exactly tell about the microbial composition and abundance. Recent researches shows that placenta is not sterile. Microbial composition in term and preterm delivery is also different. Some pathogenic microbes also colonize in placental membranes which leads towards chronic disorders related to pregnancy.


Literature explored that many scientists identified a distinct microbial community in the placenta and fetal membranes associated with severe chorioamnionitis and adverse birth outcomes. Bacteria in association with both severe poor birth outcomes and chorioamnionitis were phylogenetically different and not the most common and abundant microflora recovered in the chorioamnionitis membranes or placenta.

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