الفهرس 
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Abstract
Eighty Five samples were collected from necrotic enteritis diseased broiler chicken comprising 39 liver and 46 intestinal samples from different farms at El-Behera Governorate then, cultured anaerobically and identified phenotypically by colony characters on blood agar and by traditional biochemical methods.
Twenty samples were confirmed by PCR for genotyping of Clostridium perfringens using a specific primer for alpha toxin gene and all samples were Clostridium perfringens. Fifteen isolates were genotyped by using ERIC PCR for detection of degree of similarity between isolates. The isolates were classified into 4 genotypes.
Fifteen Clostridium perfringens strains were used for antibiotic susceptibility testing using eight antimicrobial agents and results demonstrated that all Clostridium perfringens isolates were highly susceptible to Imipeneme. Also, isolates ranged from highly susceptible to susceptible to Ampicillin and Penicillin, most of isolates were resistant to Amoxycillin, all isolates were resistant to Cotrimoxazole, Colistin and Lincomycin. All isolates showed multidrug resistance.
Overnight blood culture of twelve isolates of Clostridium perfringens were inoculated into Tryptic soy broth supplemented with of 1 % glucose to optimize biofilm growth, then biofilms were quantified by Tissue culture plate method using Eliza reader and result showed that most of isolates were moderate biofilm producers except one isolate was weak biofilm producer.
Antibiotic susceptibility testing of biofilm cells was done to detect if sensitivity of isolates to antibiotics affected after biofilm formation or not, we found that the resistance increased after biofilm formation.
The use of nanoparticles now has been emerging to overcome antibiotic resistance since, we set a trial to see the effect of silver nanoparticles on C.perfringens strains through detection of Minimum Inhibitory Concentration (MIC) & Minimum Bactericidal Concentration and on the biofilm & biofilm cells under Scanning (SEM) and Transmission Electron Microscopes . The MIC against C.perfringens was 20 µg/ ml while MBC was 30 µg/ ml.
The cells were severely affected by silver nanoparticles under TEM (rupture of cells due to damage of cell wall, gaps and shrinkage of internal contents).
It’s noted that the amount of cells in biofilm is markedly decreased when the time of exposure to MIC (20µg/ml) of silver nanoparticles increase (from 20 minutes to 1 hour up to 24 hours).
Candida albicans:
Six isolates were obtained from crop samples and confirmed phenotypically (large creamy white pasty colonies), microscopically (large gram positive cocci) and by germ tube test (formation of germ tube when incubated with human serum for 3 hours).
Biofilm formation was done in microtiter plate and the six isolates were moderate biofilm producers.
Antifungal susceptibility testing was performed using Nystatine, Amphotericin B, Fluconazole and Voriconazole before and after biofilm formation. Increased levels of antifungal medication resistance were observed in C. albicans after biofilm formation.