Probiotics are products with a sufficient number of viable micro-organisms that can alter the host's microflora to confer beneficial health effects. They are generally from human origin and are considered non-pathogenic. Prior investigators have mainly focused their research on bacteria producing lactic acid, including lactobacillus spp. and bifidobacteria spp. The mechanism of action of probiotics by which they may protect the host against a number of diseases is not fully understood but some of the suggested mechanisms are: production of antibacterial substances, modification of luminal PH, blocking bacterial adhesion sites, competition for nutrients, and reinforcement of the immune system.