Colonization of pathogenic bacteria in the gastrointestinal tract ( g.i.t. ) of the bird has been a persistent problem faced by the poultry industry. The enteropathogenic and enteroinvasive bacteria entering into the digestive tract of the chicken constantly assault the gut epithelium. The normal flora of chicken gut is a complex and dynamic ecosystem of varied microbial populations. This microflora helps in digestion and prevents colonization like Clostridium, E.coli and Salmonella. Predominant members of normal flora include microaerophilic lactic acid bacteria like lactobacilli, bifidobacteria and streptococci.
Frequent and prolonged use of gut acting antibiotics and systemic antibiotics invariably bring down the normal population of these desirable bacteria.