الفهرس 
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Abstract
In this study, the role of commercially used probiotic (Biogen, Kyolic) products in controlling the process of colonization of pathogenic E. coti and S. Enterthdis in the bird intestine. The effect of probiotics on the immune system was also investigated.
One hundred and sixty one—day—old chicks divided into 4 groups were used. The description of experimental design of these groups is presented in Table 1.
The adhered bacteria (probiotic and pathogenic) were enumerated using competition assay technique to
demonstrate the bacterial interaction during the infection process. The evaluation of humoral immune response of chicks was performed using the haemagglutination inhibition and ELISA tests. Also, the relative immuno— organs weights and food conversion ratio of the birds for each group were determined. Furthermore, tracing the changes occurring in the intestinal tract and bacterial interaction was performed using transmission electron microscope (TEM) and scanning electron microscope (S EM) techniques.
The results obtained in this work revealed that when the chicks were challenged with the enteropathogens (E. coli or S. Enteritidis) and fed with the probiotic products (Biogen or Kyolic), E. coil and S. Enteritidis were both observed to coaggregate with both probiotic products as demonstrated by scanning