Probiotics are defined as the viable microorganisms that exhibit a beneficial effect on the health of the host by improving its intestinal microbial balance. Probiotic strains, which are commonly use include Lactobacillus sp. (L. johnsonii, L. acidophilus, L. casei), Bifidobacterium (B. bifidum, B. infantis B. animalis) and the only fungal strain Sacharomycesboulardii. Following FAO recommendations probiotic strains must be able to be manufactured under industrial conditions and have to survive and retain their functionality during storage of the products: genera of the human or animal origin; stability against bile, acid and enzyme; non-pathogenicity and antibiotic resistance characteristics; ability to adhere to intestinal mucosa; colonization potential in gastrointestinal tract; production of antimicrobal substances and demonstrable efficacy and safety [1].
During the past ten years, a large number of extensive scientific researches have been carried out to demonstrate the beneficial effects of probiotic lactic acid bacteria both in humans and specially domestic animals. The main reported beneficial effects including: antimicrobial activity, enhanced immune system, balancing of colonic microbiota, reduction of fecal enzymes involved in cancer initiation, treatment of diarrhoea associated with antibiotic therapy, control of colitis and prevention of ulcers related to Helicobacter pylori.
There are different mechanisms: the competition for substrates, the prevention of pathogen adherence by specifically competing for the same receptor sites on the epithelium or mucus, or alternatively by providing an aspecific steric hindrance as a barrier to mucosal colonization, an enhancement of the host immune response against pathogens, the production of antimicrobial substances (inhibitory metabolites like organic acids (e.g. formic acid), ethanol, carbon dioxide, diacetyl, hydrogen peroxide; bacteriocins, bacteriocin-like, or non-bacteriocin substances) to remove pathogens from the intestine [2].
In addition, bacteriocins produced by lactic acid bacteria are in general active towards Gram-positive bacteria, but when the structure of their cell surface is disturbed, also Gram-negative bacteria can become sensitive. On the other hand, several probiotic strains produce antibacterial, acidic, low-molecular-mass, heat-stable, non-proteinaceous compounds with an inhibitory spectrum including both Gram-positive and Gram-negative bacteria [3].
However, the challenge for the food and pharmaceutical industries will be to conduct well-designed, multidisciplinary and multicenter clinical investigations to ascertain the health benefits or therapeutic efficacy of selected lactobacilli and bifidobacteria strains to be used as functional additives or biotherapeutic agents [4].
References:
1. K. Kailasapathy, J. Chin. Immunology Cell Biology 2000, 78(1), 80-8.
2. I.P. Kaur, K. Chopra, A.Saini, European Journal of Pharmaceutical Sciences 2002, 15, 1-9.
3. C.E. McNaught, J. MacFie, Nutrition Research 2001, 21, 343-353.
4. L. Kopp-Hoolihan, Journal of The American Dietetic Association Feb 2001, 1001(2), 229-241. |