الفهرس 
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Abstract
In the present study bacteriological examination of a total of 210 deudenal samples of broiler chickens of ages (3-4weeks) with lesions of thin-walled duodenum filled with gasses, mucosal necrosis covered by yellow-brown membrane, with or without velvety appearance and revealed that 70 samples were positive for Clostridium perfringens with a prevalence of 33.3%.
The in-vitro antimicrobial susceptibility test of 17 isolates against 10 antimicrobial agents revealed that the majority of C. perfringens isolates were multidrug resistance (MDR) with an incidence of (20%) and the higher resistance was recorded with (100%) against amoxicillin and amoxicillin-clavulanic acid, followed by cefotaxime (82.3%), ceftriaxone (76.4%) and sulfamethoxazole/trimethoprim (70.5%). While the sensitivity was (76.4%) to apramycin, (70.5%) for each of kanamycin and fosfomycin.
The biofilm formation on CRA was evaluated for 20 isolates and revealed that the isolates were 60% Positive biofilm formation.
The antimicrobial activity of (cinnamon, oregano, thyme, eucalyptus) oils were tested at concentrations of (0.5%, 0.1%, and 0.05%) against 10 MDR isolates.
The results revealed that cinnamon and oregano oils showed significant inhibitory effect at concentration of (0.5%, 0.1%, and 0.05%) on all tested isolates. Thyme oil showed significant inhibitory effect at concentration of (0.5%, 0.1%) on all tested isolates, while at (0.05%) only effect on 50%. On the other hand, the eucalyptus oil had no effect at any concentration.
The virulence of C. perfringens was examined by PCR on 5 MDR and positive biofilm activity isolates for detection of 2 virulence genes (alpha and net B) toxins. The results revealed that the tested isolates were harbored to both genes with a percentage of 100%.