Background: It has been demonstrated that the addition of a specific prebiotic mixture of galacto- and fructo-oligosaccharides to an infant formula can change the intestinal flora of formula-fed infants. The microbial composition, the metabolic end products and the pH of the feces shift in the direction of values typical for breast-fed infants. To test the relevance of the observed changes, the effect of the different short chain fatty acids, lactate and pH on the growth of opportunistic pathogens and gut commensals was tested in vitro.
Methods: Representative concentrations of D- and L-lactate and SCFA's (acetate, propionate and butyrate), either individually or in combinations, were tested in Tryptic Soy Broth in a pH-range of 5 to 7.5. Inhibition of several opportunistic pathogens (Salmonella typhimurium, Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Klebseilla pneumoniae) and some gut commensals (Lactobacillus rhamnosus, Lactobacillus plantarum and Bifidobacterium breve) by these metabolic end products was tested by comparing the individual growth curves as determined by turbidity measurements (OD600).
Results: The different SCFA's, and especially acetate, gave a concentration dependent inhibition of the different pathogens. The growth inhibition was most pronounced at lower pH values. The combination of lactate (12.5 mM), SCFA's (Acetate 25 mM, Butyrate 2.5 mM, Propionate 5 mM) and a low pH (5.5) as found in the feces of breast- and prebiotic-fed infants, almost completely inhibited all tested pathogens. The tested commensal bacteria were only slightly affected by these combinations, and in these cases sometimes even a stimulation of growth was observed.
Conclusion: Acetate, an end product of bifidobacteria in the gut of breast-fed and prebiotic-fed infants, is an efficient growth inhibitor of many common pathogens. Especially at lower pH values the growth in vitro is strongly reduced. The other SCFA's and lactate have an additive effect on the inhibition of the pathogens tested. Growth of commensals, like bifidobacteria and lactobacilli, is hardly affected under these conditions. The physiological changes induced by a mixture of galacto- and fructo-oligosaccharides can therefor be considered as an important mechanism for the inhibition of pathogens in the gut.
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van Limpt, C., Crienen, A., Vriesema, A. et al. 134 Effect of Colonic Short Chain Fatty Acids, Lactate and PH on The Growth of Common Gut Pathogens. Pediatr Res 56, 487 (2004). https://doi.org/10.1203/00006450-200409000-00157