Several studies confirm that the microbiome in the first years of life is fundamental for health in future. Even if the most of oral microbial colonization is traditionally considered to take place after birth, the beginning of the development of the microbiome seems to takes place just at the fetal level with the passage of bacteria through the placenta and then becomes more complex from birth onward [18]. The human gut is the first most rich microbiome with a great diversied microbial community, meanwhile the second is the oral cavity [19]. Many studies have shown the presence of a rich microbiome just in intestinal fetus and newborn: it is very likely that this is due to the fact that the fetus ingests large amounts of amniotic fluid during the last trimester of pregnancy. Several mechanisms have been proposed to explain how bacteria may be able to colonize the uterine cavity during pregnancy. In relation to healthy pregnancies, two main pathways are currently considered: by blood, through the placenta after translocation from the digestive tract (oral cavity and intestines) or by vertical trasmission from the vaginal tract. A recent systematic review summarize studies on oral microbiome in infants, children and adolescents: evidence indicate that a stable core microbiome is present just in newborns and it becomes more differentiated within the first four years of life [20].

In our study, the microbiological test executed at full term birth by a salivary swab, shows us the density of microbiological population in the mouth of the neonates and their mothers. We examinated the richness of oral microbial community of the babies immediately after birth, before skin to skin contact with the mother and before start breastfeeding, to reduce the influence of them on the density of the microbial community in the mouth at birth, so to accurately reflect colonization prior to and during birth. It is discussed if the delivery mode influence oral microbiome, some recent studies conclude that newborn microflora isn’t related to the kind of delivery but instead primarily driven by body habitats [1, 21]. In any case, to riduce the influence of delivery mode on microbial density, the babies of the study were born exclusively by vaginal delivery. Furthermore mothers were not given antibiotics during delivery and hadn’t taken antibiotics during the last 6 mounths of pregnancy. In spite of everything samples from the oral cavity of our neonates showed low microbial richness, infact only 4 babies had a very rich microbiome with more than 106 copies per µl. There was a statistically significant difference in the richness of the microbiome from the 60 newborns and mothers (p = 0.0001). Even comparing the microbiological density in the oral cavity of the individual mother-child pairs, we did not find a significant concordance (33.3%). It is supposed that the presence of caries in mothers don’t influence microbiome density and composition in infants in the first year of life [22, 23], results of this study seem to suggest a low influence of maternal oral microbiome on the richness of oral newborns microbiome at birth too. A so low microbiological density in the mouth of the full term babies immediately after birth could also effort the consideration that, even if the the foetal microbiome colonization may begin already in utero, oral microbiome composition matures throughout the first period of life and it is shaped by factors including host genetics and the enviroment [14]. Microbiome is a dynamic ecosystem and most of the development of the composition and function of the child’s oral microbiome occurs in the first years [20] and in particular probably just in the first hours of life [3, 4, 24]. So, the contact with the mother and our interventions on the environment around the mother and the newborn just after birth are very important for future richness and composition of the infant oral microbiome: the initial microbial exchanges between mother and infant at birth are fundamental as these early colonisers play a very important role in the development of the neonate’s immune system and long term in the activity and function of the microbiome [25].

Oral microbiome is a complex community and its composition and persistence is strictly influenced by food, oral hygiene practices and salivary flow [26]. Several studies investigate oral microbiome composition using advanced techniques of DNA sequencing, they found that the main phyla present in oral cavity are: Firmicutes, Bacteroides, Proteobacteria, Actinobacteria, Fusobacteria and Spirochaetes [20, 24, 27, 28]. To show the influence of maternal oral pathogens on the babies, we analized the presence at full term birth of major pathogenetic bacteries in oral diseases: Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum ssp.

Oral diseases are progressive, cumulative and grow in complexity over time, which is why it is very important for good oral health to be established early in life. The etiology of both dental caries and periodontal disease is polymicrobial and occurs when there is a shift in the overall ecological balance of microbes in the oral cavity [29].

It is known that the oral health and oral microbiome of a woman may directly affect her pregnancy and her developing fetus: if the mother has periodontal disease, she has higher risk for giving preterm birth, for delivering a low-birth-weight infant, for preeclampsia, and 3.4 times higher risk for preterm birth plus delivery of an infant of low birth weight [15]. So, even if there is still insufficient evidence to conclude, it has been proposed that periodontal pathogens or their products some way reach the placenta and spread beyond it to the fetus [30].

Studies have found that in the case of oral diseases (gingivitis or periodontitis), bacteria in the oral cavity may reach amniotic fluid through transient bacteremia, indicating that maternal microbes may be transmitted to the amniotic fluid with blood.

The available studies have focused their attention on the immediate complications of fetal and neonatal colonization by these pathogenic germs of the oral cavity, but it isn’t yet understood whether transmission of these pathogens is possible even in uncomplicated pregnancies, in healthy full-term infants and it is not possible to exclude that a colonization already at birth can determine a worse prognosis of oral health in the child.

The genera considered in this study, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, are all Gram negative oral pathogens responsible for periodontal disease. They are characterized by the production of various metabolites and virulence factors that lead to the destruction of periodontal tissue or inactivation of the local defenses of the immune system.

We found that the newborns’ oral cavity microbiome was composed primarily by saprophytes. The analysis of the oral microbiome showed in fact a pathological composition only in 20% of babies, this data doesn’t correlate with the incidence of periodontal pathogens in the mothers (N = 48/60; 80%). So in our samples there weren’t significative trasmission of periodontal micro-organisms and we could conclude that the oral health and oral microbiome of the mothers don’t affect a full term pregnancy. So the hypothesis of colonization in utero is still controversial and these datas would make us suspect that in some pregnancies, but not in all, there may be a bacteremia which may be followed by a complication of gestation. However, from the analysis of these data it would not be clear what is the mechanism that leads to the unleashing of bacteremia, since the presence of pathogens of the oral cavity in our 12 children did not correlate with the highest maternal bacterial charges.

Fusobacterium nucleatum was the most frequent specie detected in both mothers and babies, although again there was no correlation in the dyads. Fusobacterium nucleatum is an opportunistic periodontal pathogen of the oral cavity, but the dysbiosis can determine its pathogenicity with local and systemic consequences. We can’t determinate what influence will have for the future the presence of Fusobacterium nucleatum in the oral cavity immediately at birth but it is interesting that, even if in few babies of our sample, this bacteria was in some way able to trough the placenta also in healthy gestations.

Analysis of the other pathogenic genera of the oral cavity of our study showed a lower incidence of presence than Fusobacterium nucleatum in the oral mouth at birth. Porphyromonas gingivalis showed an higher correlation mother-babies (N = 4/12; 33%) than all the other genera examinated, so it could be the bacteria with the higher possibility of trasmission, but it is at the moment a too low evidence to demostrate it. None of the babies showed the presence of Aggregatibacter actinomycetemcomitans in their oral microbioma. Even in mothers it was the bacterium with the lowest incidence in the oral cavity.

In 4 babies there was a polimicrobial contamination too. Sometimes the association between two or more pathogens can be even more aggressive and harmful, polymicrobial infections in fact can be more serious than those caused by a single pathogen, when the interactions between individual species turn a mixed infection into a synergistic infection.

We cannot still know exactly what influence the presence of Fusobacterium nucleatum and other periodontal microorganisms in the oral cavity just at birth will have for the future infant oral health, but we could assume for these newborns a greater future risk of pathology if the balance between the different species of the microbiome under the influence of environmental factors will be broken.

In conclusion, in our study maternal oral microbiome doesn’t influence healthy, full-term newborn’s oral microbiome. There are currently not enough studies that analyze the oral microbiome at full-term birth and compare it with the maternal one. Research into oral pathogenic microorganisms in newborns has also focused on the effects on gestation, but the possible transmission to healthy full-term infants and its possible effects on long-term health has not yet been investigated. Further studies are needed.