Two experiments were carried out to evaluate the efficacy of the administration of active dry yeast and/or lactobacillus preparation (AVI-BAC), either before or after the infection with antibiotic resistant field strain of Escherichia coli O127 (E. coli O127) in controlling the severity of infection in quail chicks. The quail chicks of the different experimental groups were infected orally for two successive days with 3x107 CFU of E. coli O-127 as an individual dose. The used field strain proved to be highly pathogenic for quails. Probiotics were supplemented in the drinking water for the different treatment groups at a dose level of 0.5 gm/L. The results revealed that the inclusion of lactobacilli or active dry yeast before E. coli infection has been highly effective in reducing mortality rate, organ invasion and the number of E. coli positive quail chicks. In addition, it decreased the severity of macroscopic and microscopic lesions in different organs in the probiotic treated groups as compared
to the infected controls. Lactobacilli preparations were more efficient in controlling the severity of the infection. On the other hand, the administration of yeast and /or lactobacilli after inducing E. coli infection reduced the mortality rate and the severity of lesion score in different organs but probiotics failed to protect quail chicks against the infection. It has been proved that the two probiotics have synergistic effect in controlling collibacillosis in quails.