In general, a probiotic, is a live microorganism which beneficially affects the host animal by improving its intestinal microbial balance. The concept of probiotic evolved from Elie Metchnikoff's ideas that the bacteria in fermented products could compete with microbes that are harmful to host and are hence injurious to health. The term probiotic, meaning "for life," is derived from the Greek language. It is the antonym of the term antibiotics, was introduced in 1965 by Lilly and Stillwell as substances produced by microorganisms which promote the growth of other microorganisms. Since then several definitions for probiotics have been proposed (Table 1).

Year with reference

Lilly & Stillwell

Substances produced by microorganisms that promote the growth of other microorganisms


Schrezemeir & de Vrese

A preparation of, or a product containing, viable, defined microorganisms in sufficient numbers, which alter the microflora (by implantation or colonization) in a compartment of the host and as such exert beneficial health effects in this host


WHO/FAO report

Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host

International Life Science Institute (ILSI) Europe

a live microbial food ingredient that, when ingested in sufficient quantities, exerts health benefits on the consumer

Table 1. Some definitions of probiotic bacteria.

Table 1. Some definitions of probiotic bacteria.

The idea in the beneficial effects of probiotics is based on the knowledge that the intestinal flora can protect humans against infection and interruption of this flora can enhance susceptibility to infection. The most important sources of probiotics for humans are the bacteria in yogurt and fermented milk products.

The valuable effects of probiotics may be mediated by direct antagonistic effect against specific groups of organisms, resulting in a decrease in numbers or by an effect on their metabolism or by stimulation of immunity (Ouwehand et al.,2001; Teugheles et al., 2008; Millette et al., 2008; Tahmourespour & Kermanshahi, 2011).

Probiotics have been suggested to have the following properties and functions:

• adherence to host epithelial tissue,

• acid resistance and bile tolerance,

• elimination of pathogens or reduction in pathogenic adherence,

• production of acids, hydrogen peroxide and bacteriocins antagonistic to pathogen

• safety, non-pathogenic and non-carcinogenic, and

• Improvement of intestinal microflora (Kaur et al. 2002; Ouwehand et al. 2002).

Lactic Acid Bacteria or LAB, as the main probiotic species, are thought to be safe that have been ingested from foods without any problems for many years and are known as GRAS (Generally Recognized As Safe) bacteria that are important for animal health(Saito, 2004). The proposed mechanisms of the actions of probiotics are summarized in Fig. 5.


Maintenance of normal intestinal flora

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