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The microbiome changes with age. In general, the diversity of microbiota composition is significantly higher in adults than in children. Much of the maturation of microbiota into an adult-like configuration happens during the three first years of life.

During birth and rapidly thereafter, bacteria from the mother and the surrounding environment colonize the infant’s gut. Immediately after vaginal delivery, babies may have bacterial strains derived from the mothers’ feces in the upper gastrointestinal tract.

Infants born by caesarean section may also be exposed to their mothers’ microflora, but the initial exposure is most likely to be from the surrounding environment such as the air, other infants, and the nursing staff, which serve as vectors for transfer. The initial inoculum of babies born by cesarean section is typically dominated by Staphyloccocus, Corynebacterium and Propionibacterium species.

The primary gut flora in infants born by caesarean delivery may be disturbed for up to six months after birth, whereas vaginally born infants take up to one month for their intestinal microflora to be well established. After birth, environmental, oral and skin bacteria are readily transferred from the mother to the infant through suckling, kissing, and caressing.

In some countries there has a marked in increase in Cesarean births to  50% in countries such as China. In the US about 33%. However, research suggests that children delivered by cesarean section have an increase of asthma, and obesity, most likely due to the changes in their microbiota.

Aging does tend to decrease the diversity of the gut bacteria diversity. For example, populations of a particular group of bacteria known as bifidobacteria are known to decrease markedly after the age of about 60. This particular bacteria are known inhibitors of harmful microbes and a decline in their activities may increase susceptibility to infections.

 

References:

Arrieta, MC et al., The intestinal microbiome in early life: health and disease, Frontiers in Immunology September 2014; 5, 427

Mueller, NT et al., Prenatal exposure to antibiotics, cesarean section and risk of childhood obesity. J Obes (Lond) 2015; 39 (4): 665-670

Mesquita, DN et al., Cesarean Section Is Associated with Increased Peripheral and Central Adiposity in Young Adulthood: Cohort Study. PLoS ONE 2013; 8(6): e66827

Feehley, T et al., Microbial regulation of allergic responses to food. Semin Immunopathol September 2012; 34(5)

Wegienka, G et al., The Role of the Early-Life Environment in the Development of Allergic Disease. Immunol Allergy Clin North Am 2015; 35(1):1-17