Development of Microflora

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The GI tract is essentially sterile at the time of birth and bacterial colonization begins upon exposure to the environment. Progression of colonization is initially fast, followed by a gradual process of modification over the first few years of life. As the baby passes through the birth canal bifidobacteria and lactobacilli are typically acquired and rapid colonization of mainly enterobacteria occurs. The hospital environment, type of feeding, and type of delivery affect the early colonization of the intestine after birth. Normal vaginal birth permits the transfer of bacteria of the mother as the infant passes through the birth canal. However, with Cesarean delivery this transfer is absent and the hospital or other immediate environment can have a more significant effect on colonization. In these infants, colonization with anaerobic bacteria, especially Bacteroides, occurs later than with vaginally delivered infants.

Within the first few days and with introduction of feeding, the newborn intestine (through oxidation-reduction) promotes the establishment of aerobic bacteria, predominantly enterobacteria, Enterococcus and staphylococci, and anaerobic bacteria, bifidobacteria, Bacteroides and Clostridia. As the aerobic bacteria consume oxygen the intestinal milieu becomes more amenable to anaerobic bacteria and aerobic bacteria in turn decline. In breast fed infants bifidobacteria counts increase dramatically and account for 80-90% of the total fecal flora. Lactobacilli and Bacteroides also increase but to a lesser extent, while enterobacteria decrease. In formula fed babies Enterococcus is the predominant bacteria present with significantly less bifidobacteria and Bacteroides than the breast-fed infant. It is the difference in microflora, especially in the greater presence of bifidobacteria, and the presence of oligosaccharide and other bifido-genic factors in breast milk that likely confer a protective effect to the infant against infection, particularly against diarrheal disease.

With the introduction of weaning foods the fecal flora of babies begins to change resembling that of adults by 1 year of age. Concentrations of aerobes decrease and anaerobes (streptococci, Enterobacter, Escherichia coli, Bacteroides, and Lactobacillus) increase and predominate by 1-2 years of age. Bifi-dobacteria concentration also decreases but is generally maintained throughout adulthood (Figure 1).

Once well established the microflora is unique to each individual and maintained fairly undisturbed throughout adult life. Changes in general health



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Birth Breast feeding Adult Senescence

Figure 1 The intestinal flora and its relation to age. (purple), Bacteroides, Eubacteriae, Peptococcaceae; (red), Bifidobacteriae; (orange), E. coli, streptococci; (blue), lactobacilli; (green), Clostridiae.

and wellbeing, exposure to toxins in the food supply, and utilization of medications, particularly antibiotics, all transiently alter the colonic flora, often profoundly. When the equilibrium of this complex system occurs the host is potentially compromised. However, recovery to the original state of colonization usually occurs upon removal of the altering factors.

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Pregnancy And Childbirth

Pregnancy And Childbirth

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