Natural birth, caesarean section and the bacteria in between

What populations of bacteria accompany the baby born by natural birth compared to babies born by caesarean section, and where do the bacteria get to the baby's skin?

Dina Volodarsky Galileo

During birth, the newborn is exposed for the first time to various bacteria, first and foremost to bacteria from his mother's body when passing through the birth canal. This exposure may be a defining event in the life of the newborn, since the bacteria residing in our bodies have a great influence on our health. Thus, for example, the intestinal bacteria are known for their contribution to metabolism, to resistance to pathogenic bacteria, to the preparation of the immune system, and more.

Recently, many babies are born by caesarean section. In the United States, for example, about a third of births occur with the help of cesarean sections. In many studies in the past it was found that the population of bacteria in the intestines is affected by the mode of delivery. Now, researchers led by Maria Dominguez-Bello (Dominguez-Bello) from the University of Puerto Rico, report in an article published in June in the journal PNAS, that they discovered that the population of bacteria in the bodies of babies who are born naturally is quite different from the population of bacteria in the bodies of babies born by caesarean section, i.e. The difference is not only in the gut bacteria.

In the present study, the goal was not to focus on one type of bacteria or one organ, as was done in previous studies, but to check in general the population of bacteria in the baby's body as it depends on the mode of birth. Dominguez-Bello and her colleagues sequenced the 16s rRNA gene from samples collected near birth from the mothers and babies to characterize the bacterial populations in these samples.

16s rRNA is a component of the ribosomes of prokaryotic organisms such as true bacteria and "ancient bacteria" (archaebacteria). The ribosomes are protein "factories" of the living cell and they participate in the process where RNA is translated into protein. The gene encoding the 16s rRNA construct is used for many phylogenetic studies, because this sequence is characterized both by conserved regions, which allow it to be isolated from the rest of the genomic DNA, and by other regions in the sequence. These areas differ greatly from one taxonomic group to another, and allow identification of the bacterial species in the sample. Using such information allows reliable identification of the bacterial species.

The study was limited in scope and a total of nine women and their ten babies participated in it. Four of the women gave birth naturally, while the other five gave birth by caesarean section. The samples were taken from the skin, oral cavity and vagina of the mothers about an hour before the birth. Samples were taken from the babies' skin, oral cavity and nose five minutes after birth.

Meconium samples (the baby's first stool) were also taken within 24 hours of birth. DNA was extracted from the samples and the segments encoding the 16s rRNA construct were sequenced. At the end of the process, the exact DNA sequences of the gene coding for the 16s rRNA of the bacteria that were represented in the samples were decoded. These sequences serve as a kind of "fingerprint" of the bacteria in the sample, therefore the analysis of the sequences allows reliable identification of the variety of bacteria - the microbiome - in each of the samples.

From the findings, it appears that in mothers the bacterial populations changed mainly depending on the organ from which the sample was taken. For example, the population of bacteria on the skin of woman A was found to be more similar to the population of bacteria on the skin of woman B than to the one sampled from the oral cavity of woman A. Compared to the oral cavity where streptococci were mainly found, on the skin staphylococci were found, among others, and in the vagina (Laden) lactobacilli were mainly common.

In complete contrast to their mothers, in the babies the population of bacteria was similar between the different organs (oral cavity, skin, nose and intestine) and different between babies. These findings show that at this early stage in the baby the bacteria are uniformly distributed. An equally interesting finding is that the bacterial populations in babies born by natural birth were different from those of babies born by caesarean section. In babies who passed through the birth canal and were born naturally, bacterial populations similar to those sampled from the mothers' vaginas were found, as expected. In contrast, in babies born by caesarean section, bacteria similar to those sampled from the mothers' skin samples were found.

Moreover, in babies born by natural birth the bacteria were more similar to those sampled from their mother's vagina than to those sampled from the other mothers, while in babies born by caesarean section the bacteria were no more similar to bacteria from their mother's skin than to those sampled from the skin of the other mothers. This finding indicates that it is possible that the origin of the bacteria in these babies is not necessarily from their mother's skin, but from the hospital.

The findings described in the study may have an impact on the baby's health: the staphylococcus bacteria are usually harmless, but the MRSA strain is resistant to antibiotics and dangerous. In previous studies it became clear that 80-64% of the reported cases of MRSA occurred in newborns born by caesarean section.

Other studies have shown that babies born by caesarean section are more likely to suffer from allergies and asthma. Dominguez-Bello and her colleagues believe that the initial bacterial population affects both the patterns of bacterial settlement in the various organs over time and the developing baby's immune system.

However, the researchers are cautious in their conclusions because, as mentioned, this is a very limited study in scope, and further research is required. Moreover, interesting and important questions remain open; For example, when and how does the change from a uniform bacterial population, as found in babies, to populations adapted to the organ, as found in mothers, occur?

Dina Volodarsky has a master's degree in life sciences from the Weizmann Institute of Science and a bachelor's degree in life sciences from the Hebrew University.

The full article was published in Galileo magazine, August 2010