The intestinal ecosystem consists of three components that interact closely: the host cell, nutrients and microflora. Knowledge of the interactions among these components may be applicable for disease prevention.¹

INTESTINAL MICROFLORA

The microflora of adult humans are found primarily in the colon and distal small intestine, and consists of >10¹³ microorganisms, comprising nearly 500 species.^1,2 The microflora exist in a mutually beneficial relationship with the host, are metabolically active, and allow for the synthesis and breakdown of numerous dietary compounds. Hence, the host does not need to adapt to perform these functions. In return, the intestinal bacteria are provided a protected, nutrient-rich environment. This mutual relationship may be important in the immature or neonatal intestine, because microbial digestion avoids the need for a mature enzyme capability. For example, a major nutritional effect of intestinal microflora is the metabolism of unabsorbed carbohydrates to short-chain fatty acids, an energy source for intestinal cells, and the production of vitamin K, the predominant source of this vitamin for the infant.

In a newborn, the intestine is colonised by 12–24 h. Infant diet determines the early content of the intestinal microflora.³ Stools of breastfed infants have a predominance of Bifidobacterium and Lactobacillus species, which compete with Bacteroides, Clostridia and Enterobacteriaceae found as intestinal flora in formula-fed infants.² The bifidobacteria and lactobacilli ferment carbohydrates to produce lactic acid, creating an acidic intestinal milieu that favours the growth of non-pathogenic bacteria.⁴ By contrast, the flora of formula-fed infants ferment carbohydrates to produce carbon dioxide and water, resulting in a neutral intestinal pH. The microflora also enhance intestinal barrier function to prevent bacteria from traversing through the intestine to extraintestinal sites: a process called bacterial translocation. The lactic acid bacteria do not translocate, and they produce bacteriocins that have antimicrobial functions and …