Interaction of bifidobacteria with ferric iron

Bifidobacteria are probiotics that have been implicated in a number of beneficial actions in humans and animals. It is estimated that 20-30% of bifidobacteria consumed will enter the colon from the ileum, and that this quantity is sufficient to exert an influence on colon physiology. There are many reasons why probiotics exert a beneficial effect on their host organism. This paper focuses on one of them: the interaction of bifidobacteria with ferric iron in the form of Fe(OH)(3) and iron-saturated lactoferrin. Lactoferrin can donate its iron to Bifidobacterium breve for growth purposes, and so can its C-terminal domain fragment. Fe(OH)(3) is surface-bound by Bifidobacterium thermophilum in a biphasic manner: the rapid initial phase and a slower process, the extent of which may depend on the presence of free radicals in the medium. The latter alter the bacterial surface, resulting in greater binding of Fe(OH)(3) by the bacteria. Free radical scavengers such as lactate and g(l)ucose counteract cell surface damage and lower the extent of Fe(OH)(3) binding. Free radicals thus serve to increase iron binding by bifidobacteria making it less available to pathogens. (C) 1998 Elsevier Science Ltd. All rights reserved.