See “Bacterial Community Structure Associated With Elective Cesarean Section Versus Vaginal Delivery in Chinese Newborns” by Yu et al on page 240.
Microbes that live on and inside the human body (microbiota) consist of more than 100 trillion microbial cells and outnumber the host cells. Commensal bacteria provide a wide range of metabolic functions that the human body lacks. They facilitate diverse processes such as digestion, absorption, and storage of nutrients, and protection against pathogen colonization through competition for nutrients, secretion of antimicrobial substances, and microniche exclusion. Commensal bacteria also promote angiogenesis and development of the intestinal epithelium and have been shown to be essential for the normal development and function of the immune system. Although we know the essential role of the microbiome in maintaining the health status of the host, little is known about when the initial colonization of gut microbiome occurs. Recent evidence suggested that the initial colonization may be before birth (1,2) and seeded from the maternal environment. Furthermore, in early childhood, the gut microbiome was unstable and affected by birth mode, antibiotic usage, changes on feedings, and many other environmental factors. In this issue of the Journal of Pediatric Gastroenterology and Nutrition, Yu et al describe how 41 Chinese newborns were recruited and their day 2 and day 4 postdelivery fecal samples were characterized to compare the composition and diversity of the intestinal microbiota by the delivery status, vaginally (VD) or by cesarean section (CD) (3). In spite of the experimental design in the Yu et al study using the denaturing gradient gel electrophoresis combined with culture-based colony polymerase chain reaction and Sanger sequencing being less informative than the bacterial 16S ribosomal RNA deep sequencing approach, it was concluded that the composition and overall structure of gut microbiome in infants were substantially different by delivery mode in Chinese newborns, which is consistent with the findings by other ethnic groups (4,5). In particular, a sample from VD infants showed enrichment of Escherichia coli and Bacteroides, which are commonly found in gut microbiota, whereas enriched Staphylococcus in CD infants was commonly found on skin. Those differential microbiome signatures suggest the possible seeding origins of varied bacterial strains in the infant gut; however, commonly found vagina-enriched Lactobacillus was observed in neither VD nor CD samples of the present study. Interestingly, when comparing day 2 and day 4 samples, it was observed that certain taxa such as Veillonella sp and a Neisseria mucosa strain were present only in day 4 samples and they are not differentiable by delivery mode. Those taxa may be seeded through later contact with the parents or the caregivers.
Overall, the Yu et al study demonstrated the effect of delivery mode on the diversified intestinal microbiota in Chinese newborns. With the economic expansion in the last 20 years in China, dramatic changes have occurred in the entire society, and increasing elective CD and many other environmental factors may affect the gut microbiome abundance and composition in early life and increase the risk in an infant's later development. Therefore, a more extensive multicenter study is essential to evaluate samples obtained from a larger Chinese population using more advanced technology with a high sensitivity and resolution to fully assess the impact of the delivery mode on the intestinal microbiota of Chinese infants.
1. Ardissone AN, de la Cruz DM, Davis-Richardson AG, et al. Meconium microbiome analysis identifies bacteria correlated with premature birth. PLoS One
2. Hu JZ, Nomura Y, Bashir A, et al. Diversified microbiota of meconium is affected by maternal diabetes status. PLoS One
3. Liu D, Yu J, Li L, et al. Bacterial community structure associated with elective cesarean section versus vaginal delivery in Chinese newborns. J Pediatr Gastroenterol Nutr
4. Azad MB, Konya T, Maughan H, et al. Gut microbiota of healthy Canadian infants: profiles by mode of delivery and infant diet at 4 months. CMAJ
5. Dominguez-Bello MG, Costello EK, Contreras M, et al. Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. Proc Natl Acad Sci U S A