During the first year of life, many factors can change the developing baby’s gut microbiome.
Genetics, mom’s health status, mode of delivery, gestational age, feeding regime, and antibiotic use are known to have an influence.
From birth through weaning, the intestinal microbiome composition has a significant impact on infant gut health. During this time, key microbial species are colonized – Streptococcus, Staphylococcus, and Enterobacter.
Initial exposure to the microbial environment around the infant can have a major impact on infant gut microbiota development. External factors, such as mom’s health status, mode of delivery (C-section or vaginal birth), gestational age, and feeding regime (breastmilk or formula) can impact colonization and flu of microorganisms during this critical life period.
GI MICROBIAL DEVELOPMENT AT BIRTH
Full-term C-section-delivered infants were found to have increased abundance of Firmicutes and lower abundance of Actinobacteria, evident even after the first week of life. Preterm infants, however, displayed a greater abundance of Proteobacteria compared to the infants who reached full-term. Also, the gut microbiota of full-term C-section infants resembled that of vaginally-delivered infants at 8 weeks of life.
Previously, preterm infant guts have been characterized by delayed microbial colonization with reduced levels of anaerobic taxa, such as Bifidobacterium and Bacteroides. Gut microbiota development in preterm infants have been found to correlated with the baby’s post-conceptual age.
Maternal-infant transmission of mother’s lactobacilli predominantly occurs when the baby is delivered vaginally. It is understood that the birth canal harbors lactobacilli to reduce the pH of the intestines and prevent growth of potentially pathogenic microorganisms in the baby’s gut.
A number of studies have also begun to look at the microbial communities found in breastmilk. Members of the “core” breastmilk microbiome include Streptococcus, Serratia, Pseudomonas, Corynebacteria, Ralstonia, Propionibacterium, Sphingomonas, and Bradyrhizobiaceae. Other studies have also identified horizontal transfer of Lactobacillus, Staphylococcus, Enterococcus, and Bifidobacterium from breastmilk to the infant gut.
Some studies have also begun to focus on microbial colonization that may occur during pregnancy. There is some evidence that the baby may be colonized at a low abundance prior to being born.
HUMAN MILK OLIGOSACCHARIDES (HMOs)
Prebiotics are described as “selectively fermented ingredients that result in specific changes in the composition and/or activity of the GI microbiota, thus conferring benefit(s) upon host health”.
Human breastmilk is a natural prebiotic that contains essential nutrients and growth factors required for development of a healthy gut microbiome. This is one of the reasons why exclusive breast feeding is thought to be so beneficial – the provision of HMOs and glycoconjugates to aid in the selective proliferation of healthy intestinal bacteria. HMOs are not digested by the baby. Instead, they reach the colon intact and act as an essential substrate for the growth of beneficial bacteria. Evidence suggests that breastmilk may be even more beneficial to C-section infants (who were not exposed to the same bacteria as their vaginally born cousins).
The infant gut microbiome does not fully develop until the baby reaches 2-3 years of age. Therefore, it is important to recognize the changes occurring in the baby’s gut during this transitional period from early infant feeding to solid foods. The World Health Organization states the appropriate age for complimentary feeding as typically “6 to 23 months of age”.
The transition from breastfeeding to “family” foods rich in fiber and protein significantly affects development of the infant gut microbiome. Digestion of these foods provides fermentable substrates necessary for the growth of colonic bacteria.
For formula-fed babies, evidence suggests the beneficial use of prebiotics, galacto- and fructo-oligosaccharides to help maintain a well-balanced microbial progression from infancy to early adulthood.
HEALTH BENEFITS OF PROBIOTICS
Probiotics – live microorganisms that, when administered in adequate amounts, confer a health benefit on the host – have been looked at as potential prophylactics and/or treatments to re-establish gut homeostasis. Probiotic treatment is being studied in different conditions associated with gut disturbances such as necrotizing enterocolitis (NEC), childhood obesity, and autism.
NEC is a condition where portions of the bowel undergo necrosis (cell death) and is the second most common cause of death in preterm infants. In a comprehensive review, it was found that enteral administration of probiotics reduced incidence of severe NEC and NEC-related mortality.
METABOLIC SYNROME AND OBESITY IN CHILDHOOD
metabolic syndrome relates to any case of insulin resistance found in the presence of at least two of the following risk factors: hypertension, obesity, high triglyceride levels, or reduced high-density lipoprotein cholesterol levels. While preliminary animal trails found probiotics to improve glucose-insulin levels and hepatic steatosis in a high-fat diet, human clinical trials have not produced adequate evidence.
The cause of autism spectrum disorder – characterized by a deficit in social and communicative interactions – is unclear. However, recent studies have shown a link between symptomatic cognitive dysfunction and GI distress through a connection in the central nervous system in what has become know as the “gut-brain axis”. There is some evidence that probiotics alleviate GI distress in various mouse models that mimic the symptomatic traits of autism.