The ability of probiotics to protect chicks against S.typhimurium was evaluated. Challenge experiment was designed using
120 one day old chicks divided into 4 groups. The challenging S. typhimurium was counted in liver and cecum samples
and the results shows that counts of the probiotics pre-treated group were significantly reduced when compared to those
of positive control group. The phagocytic percent of chicks of positive control group were 38.40%, 26% and 18% while
that of pre-treated group were 54.20%, 38.10% and 36.40% in 7, 14 and 21 days old respectively. Phagocytic indexes
(PI) of positive control group were 1.0±0.10, 1.0±0.20 and 1.0±0.0 while those of pre-treated group were 1.50±0.20,
1.10±0.08 and 1.10±0.04in 7, 14, and 21 days old respectively. S. typhimurium from ceacal digesta were used for
extraction of total RNA to assess the expression of 4 virulence genes (hilA, hilC, hilD and sipC) using Real Time PCR.
The obtained data revealed that CT means of hilA, hilC, hilD and sipC of control group and pre-treated group were as
follow 20.31 and 17.68, 17.43 and 16.85, 17.03 and 16.72 and 18.78 and 17.98 respectively. It was concluded that
probiotics has an impact on S. typhimurium and caused an imbalanced virulence gene expression.