ne of the most interesting aspects

ne of the most interesting aspects of probiotic supplementation is directed towards the immune response.
In a human trial, 24 subjects were fed 450 g of yoghurt
per day for 4 months, and showed signi"cant increase in
the production of c-interferon (Halpern, Vruwink, Van
de Water, Keen & Gershwin, 1991). In animal models,
probiotics have been shown to stimulate the production of antibodies (local and systemic), enhance
the activity of macrophages, increase c-interferon levels
and increase the concentration of natural killer cells.
Obviously, the non-pathogenic nature of the probiotic is
crucial.
6. Mechanisms of probiotic activity
The exact manner in which probiotics may achieve
their e!ect(s) is still uncertain. However, a number of
mechanisms may be speculated upon:
6.1. Biochemical ewects
One mechanism by which organisms may inhibit one
another is via the production of bacteriocins (Meghrous,
Euloge, Junelles, Ballongue & Petitdemange, 1990). Gibson and Wang (1994) suggested that some strains of
bi"dobacteria could inhibit a variety of pathogenic bacteria, through a non-pH related e!ect. However,B. bixdumwas found to excrete a bacteriocin which a!ected
Listeria, Enterococcus, Bacillus, Lactobacillus, Leuconstoc
andPediococcus(Anand, Srinivasan & Rao, 1984). Other
bacterial species known to produce bacteriocins, include
lactobacilli and lactococci (Talarico & Dobrogosz, 1989).
Short chain fatty acids (SCFA) are also produced in
varying quantities as metabolic end products by
probiotic bacteria, and it is thought that these may induce an antagonistic e!ect against other organisms.
A lowering of the gut pH may act directly to inhibit the
growth of harmful and pathogenic organisms.
6.2. Competition for nutrients
Certain bacterial species have exact nutritional requirements and it is likely that one population utilises
nutrients at the expense of other species. This competitive
interaction may be forti"ed through probiotic use.
6.3. Immune ewects
The potential of the immune response to control the
growth of micro-organisms in the gut is an important
consideration. Further work may establish how stimulation of the systemic components of the immune system,
through non-pathogenic means, can help regulate the gut
micro#ora.
6.4. Colonisation
One possible mechanism for the action of probiotics is
their ability to adhere to the intestinal mucosa. As such,
they can resist peristalsis and occupy a niche at the
expense of harmful organisms.
7. Prebiotics
As the viability of live bacteria in food products and
during transit through the gastrointestinal tract may be
variable, the prebiotic concept has been developed. Here,