Oligosaccharides in human milk: structural, functional, and metabolic aspects.
Kunz C, Rudloff S, Baier W, Klein N, Strobel S Institut fur Ernahrung, Universitat Giessen, 35392 Giessen, Germany. email@example.com
Annu Rev Nutr 2000;20:699-722
Research on human milk oligosaccharides (HMOs) has received much attention in recent years. However, it started about a century ago with the observation that oligosaccharides might be growth factors for a so-called bifidus flora in breast-fed infants and extends to the recent finding of cell adhesion molecules in human milk. The latter are involved in inflammatory events recognizing carbohydrate sequences that also can be found in human milk. The similarities between epithelial cell surface carbohydrates and oligosaccharides in human milk strengthen the idea that specific interactions of those oligosaccharides with pathogenic microorganisms do occur preventing the attachment of microbes to epithelial cells. HMOs may act as soluble receptors for different pathogens, thus increasing the resistance of breast-fed infants. However, we need to know more about the metabolism of oligosaccharides in the gastrointestinal tract. How far are oligosaccharides degraded by intestinal enzymes and does oligosaccharide processing (e.g. degradation, synthesis, and elongation of core structures) occur in intestinal epithelial cells? Further research on HMOs is certainly needed to increase our knowledge of infant nutrition as it is affected by complex oligosaccharides.
[Effects of oral administration of bifidobacteria on intestinal microflora in premature and newborn infants].
[Article in German]
Uhlemann M, Heine W, Mohr C, Plath C, Pap S Kinder- und Jugendklinik der Universitat Rostock.
Z Geburtshilfe Neonatol 1999 Sep-Oct;203(5):213-7
In a prospective, randomised study the effects of orally administered bifidobacteria on the intestinal microflora were investigated in 100 preterm and term neonates under intensive care conditions during the first 21 days of life. The 50 infants (group with bifidobacteria) received lyophilized bifidobacteria (Topfer Bifidus) via nasogastral tube with an initial dosage of 3 times daily 1.25 x 10(8) bifidobacteria on day 2 of life and a daily dosage of 6 times 1.25 x 10(8) bifidobacteria on day 3 until day 21 of life. The other 50 infants (control group) did not receive bifidobacteria. The preterm and term neonates were fed either with pasteurized mother's milk or milk from healthy female donors (n = 79) or with an infant formula (Alfare, n = 13) or initially with Alfare and thereafter with mother's milk (n = 8). The intestinal microflora of preterm and term neonates under intensive care conditions could be influenced by the oral administration of bifidobacteria. The administration of bifidobacteria resulted in the group of inoculated infants in a significantly earlier colonization of bifidobacteria (8.1 3.9 days of life) than in the control group (11.3 4.7 days of life). On day 7 a bifidobacterial dominance (> 90% of the intestinal microflora) could be found in 26% of infants with inoculation of bifidobacteria and only in 2% of the control group (p < 0.001). These significant differences could be shown until day 21 of life. A difference in septicemia frequency between the two groups could not be demonstrated. At the beginning of the infection a bifidobacterial dominance was found in only one of 23 cases of septicemia.
Protective effect of bifidus milk on the experimental infection with Salmonella enteritidis subsp. typhimurium in conventional and gnotobiotic mice.
Silva AM, Bambirra EA, Oliveira AL, Souza PP, Gomes DA, Vieira EC, Nicoli JR Departamento de Microbiologia, Faculdade de Medicina, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
J Appl Microbiol 1999 Feb;86(2):331-6
The ability of Bifidobacterium bifidum from a commercial bifidus milk to antagonize Salmonella enteritidis subsp. typhimurium in vivo, and to reduce the pathological consequences for the host, was determined using conventional and gnotobiotic mice. Conventional animals received daily, by gavage, 0.1 ml bifidus milk containing about 10(9) cfu B. bifidum and germ-free animals received a single 0.1 ml dose. The conventional and gnotobiotic groups were challenged orally with 10(2) cfu of the pathogenic bacteria 5 and/or 10 d after the beginning of treatment. Control groups were treated with milk. Bifidus milk protected both animal models against the challenge with the pathogenic bacteria, as demonstrated by survival and histopathological data. However, to obtain the protective effect in gnotobiotic animals, the treatment had to be initiated 10 d before the challenge. In experimental and control gnotobiotic mice, Salm. enteritidis subsp. typhimurium became similarly established at levels ranging from 10(8) to 10(9) viable cells g-1 of faeces and remained at these high levels until the animals died or were sacrificed. It was concluded that the protection against Salm. enteritidis subsp. typhimurium observed in conventional and gnotobiotic mice treated with bifidus milk was not due to the reduction of the intestinal populations of the pathogenic bacteria.
Modification of colonic fermentation by bifidobacteria and pH in vitro. Impact on lactose metabolism, short-chain fatty acid, and lactate production.
Jiang T, Savaiano DA Department of Pediatrics, University of Iowa Hospitals and Clinics, Iowa City 52242, USA.
Dig Dis Sci 1997 Nov;42(11):2370-7
Colonic fermentation plays an important role in the prevention of lactose intolerance and intestinal disorders. The objectives of this study were to evaluate whether supplementation with bifidobacteria modify colonic fermentation of lactose and short-chain fatty acid production and to assess influence of the pH in an in vitro continuous culture system. There was a significantly greater reduction in lactose concentrations at pH 6.7 than that at either pH 6.2 or pH 5.7, accompanied by the highest beta-galactosidase activity and D-lactate production. Bifidus supplementation reduced lactose and D-lactate concentrations and increased acetate production at pH 6.7. The study demonstrates that lactose is rapidly metabolized by colonic bacteria and lactose fermentation in vitro is pH dependent with a maximum rate at pH 6.7. Bifidobacteria supplementation may have the potential to improve lactose fermentation and to manipulate SCFA and lactate production.
Effect of yogurt and bifidus yogurt fortified with skim milk powder, condensed whey and lactose-hydrolysed condensed whey on serum cholesterol and triacylglycerol levels in rats.
Beena A, Prasad V Department of Dairy Science, Veterinary College, Kerala, India.
J Dairy Res 1997 Aug;64(3):453-7
The possible hypocholesterolaemic properties of milk and fermented milk products have been investigated in groups of albino rats given a basal diet, basal diet plus cholesterol, and basal diet plus cholesterol together with whole milk or standard or bifidus yogurt. The yogurts were fortified with skim milk powder, condensed whey or lactose-hydrolysed condensed whey. After 30 d, triacylglycerols, total cholesterol, HDL-cholesterol and LDL-cholesterol were measured in serum. Whole milk and ordinary yogurt had no hypocholesterolaemic effect, but standard yogurt containing lactose-hydrolysed condensed whey and all bifidus yogurts lowered serum cholesterol. In general, yogurts changed HDL-cholesterol little, but tended to raise triacylglycerols. There was marked lowering of LDL-cholesterol in rats given either type of yogurt fortified with whey proteins. This study has demonstrated in a rat model that bifidus yogurts and yogurts fortified with whey proteins can reduce total and LDL-cholesterol, and suggests that if they have the same effect in human subjects they have potential value in cholesterol-lowering diets.
In vitro inhibition of Helicobacter pylori NCTC 11637 by organic acids and lactic acid bacteria.
Midolo PD, Lambert JR, Hull R, Luo F, Grayson ML Department of Microbiology, Monash Medical Centre, Clayton, Victoria, Australia.
J Appl Bacteriol 1995 Oct;79(4):475-9
In this study the effects of both pH and organic acids on Helicobacter pylori NCTC 11637 were tested. Lactobacillus acidophilus, Lact. casei, Lact. bulgaricus, Pediococcus pentosaceus and Bifidobacterium bifidus were assayed for their lactic acid production, pH and inhibition of H. pylori growth. A standard antimicrobial plate well diffusion assay was employed to examine inhibitory effects. Lactic, acetic and hydrochloric acids demonstrated inhibition of H. pylori growth in a concentration-dependent manner with the lactic acid demonstrating the greatest inhibition. This inhibition was due both to the pH of the solution and its concentration. Six strains of Lact. acidophilus and one strain of Lact. casei subsp. rhamnosus inhibited H. pylori growth where as Bifidobacterium bifidus, Ped. pentosaceus and Lact. bulgaricus did not. Concentrations of lactic acid produced by these strains ranged from 50 to 156 mmol l-1 and correlated with H. pylori inhibition. The role of probiotic organisms and their metabolic by-products in the eradication of H. pylori in vivo remains to be determined.
[Development, equilibrium and role of microbial flora in the newborn].
[Article in French]
Ducluzeau R Laboratoire d'Ecologie et de Physiologie du Systeme Digestif, INRA-CRJ, Jouy-en-Josas.
Ann Pediatr (Paris) 1993 Jan;40(1):13-22
Development of the digestive tract intestinal flora is the result of a specific selection process to which the multiple maternal or environmental bacteria that penetrate into the neonatal gut are subjected. In breast-fed infants, Escherichia coli and streptococci are the first bacteria to appear in the gut. They are usually, but not always, followed by a population of Bifidobacterium which quickly becomes predominant. In bottle-fed infants, the intestinal flora is more variable and often includes, in addition to the organisms mentioned above, other enterobacteria and a wider range of obligate anaerobes. Studies of experimental models have shown that the nature of milk fed to the offspring and even the lactating mother's diet have substantial effects on the sequence of development of the neonatal intestinal flora. A large number of factors capable of inhibiting or permitting in vitro growth of various bacterial species have been identified in milk. However, no in vitro activity of these factors added to milk has ever been demonstrated. These factors include "bifidus factors", which promotes the growth of Bifidobacterium, and lactoferrin and immunoglobulins, which prevent colonisation of the gut by pathogenic enterobacteria. Immune factors in milk play a key role in interactions between the microbial flora and gut mucosa. However, they seem to have no effect on the growth of bacterial populations in the gut lumen. A number of pioneer bacteria, which are the first to arrive in the gut, are capable of effectively blocking growth of other bacteria introduced later in the ecosystem. In some instances, these pioneer bacteria also inhibit production of toxins by pathogenic species. Consequently, it is important to adhere to the recommended gradual changes in diet which allow these species to sequentially colonize the gut.
Iron-binding proteins and other factors in milk responsible for resistance to Escherichia coli.
Ciba Found Symp 1976;42:149-169
Human milk contains large amounts of the iron-binding protein lactoferrin. This is normally unsaturated with iron. It also contains large amounts of IgA and small amounts of IgG and IgM. A combination of lactoferrin and specific antibody has a powerful bacteriostatic effect on Escherichia coli. In sucking infants the milk proteins probably reach the small intestine intact. Experiments with sucking guinea pigs show that milk suppresses E. coli in the gut and that the unsaturated iron-binding protein plays an essential role in the bacteriostatic reaction. Inhibited E. coli appear to be acutely iron deficient. E. coli growing slowly in iron-deficient media show abnormal forms of certain aminoacyl tRNAs. In bacteria inhibited by colostrum the proportion of abnormal tRNA is as high as 90%. These abnormal tRNAs are converted to the normal form by the addition of iron. This occurs in the absence of further RNA synthesis and is accompanied by renewed bacterial growth. The normal flora of the gut also plays an important role in resistance. Human milk has a low buffering capacity and bacterial fermentation of lactose produces a low pH.e. coli is inhibited by acetic acid/acetate buffer at pH 4.8-5.6, whereas these conditions allow normal growth of Lactobacillus bifidus. The faeces of babies fed on breast milk have a low pH, low counts of E. coli and high counts of L. bifidus. Artificially fed babies have more alkaline faeces which contain few L. bifidus and large numbers of E. coli.