Title: Gut microflora and infant health


Key words: infant rearing, gut microflora, bottle feeding, bifidobactera, E. coli, breast feeding, lactobacilli, organic vegetable, vaginal flora, vegan, meat, clostridia, atopic, Th2, IgA, leaky gut, hygiene hypothesis, allergic, infectious, URTI, upper respiratory tract infections, ear infections, otitis, lactobacillus GG, rotavirus, gastroenteritis, probiotic, prebiotic, fructooligosaccharide, short chain fatty acid, vitamins,  


Date: Sept 2006


Category: The Gut


Nutrimed Module:


Type: Article


Author: Morgan, G


Gut microflora and infant health


Infant rearing practices are known to affect infant and childhood health and possibly to have longer-term effects. Differences in rearing practices between developing and developed countries reflect traditional and Westernised cultural traditions and these, as well as economic factors, have an impact on health issues. The effect of infant dietary practices on the gut microflora and the possible beneficial effects of manipulating this environment is reviewed in this article. 


The composition of the infant gut microflora has changed significantly over the last 50 years with the spread of Western dietary practices (Lundequist 1985). Increased bottle-feeding in developing countries is partly responsible for these changes (Yoshiota 1991). At birth the microflora consists predominantly of bifidobacteria, aerobes such as E. Coli and anaerobes such as bacteroides (Finegold 1983, Lundequist 1985). Breast-feeding helps to maintain higher levels of beneficial bifidobacteria (Kok 1996), but, regardless of feeding practice, there is a move towards increasing diversification of the flora in the first few months of life, anaerobes such as bacteroides becoming predominant (Lundequist 1985, Benno 1991).


Cultural factors other than bottle-feeding are also operative: bifidobacteria tend to predominate in Japanese infants (Yoshioka 1983), and lactobacilli in South Indian, Ugandan and Estonian infants (Sepp 1997), for example. These differences are thought to reflect a greater reliance on organic vegetable produce as against a more processed Western diet (Bjorksten 2001). Imprinting by the maternal vaginal flora may also be a factor (Lundequist 1985). In the Western context, differences between vegan and meat consuming parents and their offspring correspond to these epidemiological observations (Sepp 1997).


Variations in gut microflora are now known to impact on the maturation of the immune system. ‘Beneficial bacteria’ such as bifidobacteria and lactobacilli which flourish at low pHs exert an inhibitory effect on certain pathogenic strains of clostridia and E.Coli (Gibson 1994). Low bifidobacteria counts at 3 weeks, for example, is inversely related to clostridial counts and is a predictor of atopic disease at 12 months (Kalliomaki 2001a). Likewise lactobacilli supplementation during the first 6 months of life has been found to protect against later atopy (Kalliomaki 2001b).


There is now much evidence that the predominant Th2-type response characteristic of intra-uterine and neonatal life (Bjorksten 1997a), and which is associated with atopic and inflammatory diseases, is downregulated through the action of certain bacteria such as bifidobacteria and lactobacilli that promote Th1-type immunological responses (Bjorksten 1997b). Th2-type responses have also been linked to impaired IgA secretion in the gut and respiratory mucosa, predisposing to viral and bacterial infections, food intolerances and the ‘leaky gut syndrome’ (Wanke 2001, Kalliomaki 2001b).


The switch to a more Th1-modulated immune response may be modulated by a further subset of T-helper cells, the Th3 line (Murch 2000). Th3 cells have been shown to downregulate TGF-beta and IL-10 cytokine production (Murch 2000, Kalliomaki 2001b). Disturbances of these cytokines have been related to atopy, Th1 responses and bifidobacteria status (Hessle 2000, Kalliomaki 2001b). IL-12 production stimulated by gram-positive bacteria may also modulate these responses (Hessle 2000). Research findings such as these have led to the formulation of the ‘Hygiene Hypothesis’ (Holt 1997, Murch 2000), which proposes that a level of bacterial infection in early life is essential for the evolution of a normal ‘healthy’ bowel flora, the development of balanced Th1/Th2 responses, and the prevention of atopic, allergic, infectious and other diseases in later life.


In clinical practice, healthier immune profiles associated with favourable dietary practices have been associated with lower rates of atopic disease, upper respiratory tract and ear infections (Braback 1995, Bjorksten 2001). In the trial mentioned (Kalliomaki 2001b), supplementation with the strain lactobacillus GG during the first 6 months of life reduced the incidence of atopic eczema by half. In another trial (Hatakka 2001), supplementation with milk probiotics led to significant reductions in upper respiratory tract and otitis media infections.


Common bowel infections, such as rotavirus-associated gastoenteritis, have been shown to be benefited by probiotic treatment (Majamaa 1995). Work by Gibson and Roberfroid has shown the ability of prebiotics such as fructooligosaccharides to increase the numbers of beneficial bacteria such as bifidobacteria and to reduce those of pathogens such as clostridia (Wang 1993, Gibson 1995a, Gibson 1995b). Such changes lead to increased production of beneficial short chain fatty acids, vitamins and other substances (Gibson 1995a) which have a favourable effect on the immune system, the benefits of which have been pointed out. Their efficacy in modulating the infant gut microflora has been demonstrated (Gibson 1995b).


Further work needs to be carried out to demonstrate their clinical efficacy and the possible increased efficacy of combining prebiotics with probiotics as synbiotics.




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