الفهرس 
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Abstract
The importance of Bacillus bacteria is increasing day after day. They are considered potential alternatives for antibiotics due to their antimicrobial activity against most pathogenic bacteria. The goal of the present study was to isolate and identify Bacillus species with antimicrobial activity. A total of 110 intestinal samples taken from broiler chickens of different ages (3- 5 weeks) from different retail markets in Cairo were examined bacteriologically to detect bacilli. Escherichia coli, Proteus species and Bacillus species were isolated. The Bacillus isolates were confirmed by VITEK, PCR, sequencing of the 16S rRNA gene and phylogeny. Thirty two bacilli species (17 Bacillus amyloliquefaciens, 7 Lysinibacillus sphaericus, 3 Bacillus cereus, 2 Bacillus licheniformis and 2 Lysinibacillus macrolides and one Bacillus altitudinis) were detected. The isolates were screened for their antimicrobial activity against indicator Gram negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Salmonella Enteritidis), Gram positive bacteria (Staphylococcus aureus and Listeria monocytogenes), and Yeast (Candida albicans) using cross streak, disc diffusion and well diffusion agar methods. The best inhibition results were achieved by cross streak method and disc diffusion method. S. aureus, L. monocytogenes and Candida albicans were the most sensitive indicator bacteria followed by Salmonella Enteritidis then Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli. Interestingly, using the cross streak method, and disk diffusion method of the whole bacterial culture, showed that nearly all the tested bacilli could possess their antimicrobial activity against the indicator bacteria. On the other hand, by using well diffusion method of the culture filtrate, all the tested bacilli couldn’t inhibit the growth of the indicator bacteria except Bacillus amyloliquefaciens that showed inhibition activity against S. aureus, and Escherichia coli. These findings demonstrate that the local spore forming isolates have probiotic properties which can be further developed as poultry feed additive or used in further industrial uses. In addition, the cross streak method and the disk diffusion method were suitable for a preliminary assessment of the antagonistic effects of the isolates.