الفهرس 
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Abstract
Objectives of the present study were to investigate the prevalence of clostiridium perfringens among broiler with or without coccidial infections in Assiut Governorate, isolate and identify the causative agent associated with NE from various farm of different ages, detect the toxin genes in the isolate by The polymerase chain reaction assay (PCR), investigate the occurrence of C. perfringens NetB toxin gene, Determination of the in-vitro resistance of C. perfringens to some antibiotics which are relevant to poultry production (for treatment, prophylaxis and growth promotion) and evaluation of some antibiotics and probiotics for control of C. perfringens. To achieve these objectives a total of 120 intestines from freshly dead and sacrificed broiler chicken (2 – 6 weeks old) were collected from private farms in Assuit Governorate. The collected samples were classified to groups according to coccidial infestation. Collected samples were examined bacteriologically for possible recovery of C. perfringens.
The current study revealed the following results:
• A number of 35 C. perfringens isolates were successfully isolated with an incidence of 29.17%. All isolates were morphologically and biochemically identified.
• The incidence of C. perfringens was 48.57% (17/35) in the group of birds showing necrotic enteritis and positive for coccidiosis and 51.43% (18/35) in the group of birds showing necrotic enteritis and negative for coccidiosis.
• According to age susceptibility, the highest incidence of C. perfringens was detected in older birds (29 – 35 day - old), while the incidence was low in young birds (15 – 22 days old )
• Toxin genotyping of 22 C. perfringens isolates by uniplex and multiplex PCR revealed that 11 isolates were only positive to alpha toxin gene and indicated that type A was the most predominant etiology in the occurrence of NE in Assuit Governorate.
• 2 (18%) of the selected toxigenic C. perfringens type A isolates were positive for NetB toxin indicated that there may be other factors, besides NetB, that allow C. perfringens type A to cause tissue damage similar to necrotic enteritis.
• Calculation of multidrug resistant index (MDRI) revealed that all C. perfringens isolates demonstrated multiple resistances ( resistant to about 5 to 15 of antibiotics).
• High prevalence of resistance were observed to Neomycin, Sipramycin, Lincomycin and Clindamycin (100%), Flumiquine and Erythromycin (90. 09%) Streptomycin, Florfenicol and Doxycyclin (81.82%), Gentamycin, Colistin, Cephradine and Naledixic acid (72.73%), however, resistance to Amoxicillin (45.5%) and Ampicillin (63.6%) were low (beta- (β-) lactamase was not demonstrated in C. perfringens isolates in Assuit Governorate).
• Amoxicillin was effective in control of C. perfringens induced necrotic enteritis as expressed by reduction of clinical signs, mortalities and intestinal lesion scores as well as improving the performance parameters in broiler chickens.
• Evaluation of the effect of lactobacillus probiotic on expirmentally infected chicks indicated that use of lactobacillus as probiotic has great effect in protection against challenge with coccidian oocyst and toxigenic C. perfringens by increase body weight and decrease feed conversion rate and necrotic enteritis lesion score.