الفهرس 
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Abstract
In this study a total number of 225 retail meat and offal samples (156 chicken meat and offal samples and 99 beef meat samples) were collected from tow governorates (Giza and Qalubia) for isolation of Bacillus spp samples were obtained either from butchers shops (chicken and local beef meat) and supermarkets (frozen imported meat) for one year. The meat samples consisted of 156 chicken samples (65 breast meat, 48 thigh meat, 29 livers and 14 hearts), 59 local beef meat (44 meat cut and 15 minced meats) and 40 imported frozen beef meat. Bacillus spp isolates were 48.6% from total samples (124 isolates), divided into 66 (42.3%) from chicken samples (26 from breast, 24 from thigh, 10 from liver and 6 from heart) and 58 (58.6%) from beef meat samples (23 from local meat cut ,7 from local minced meat and 28 from imported frozen meat cuts). Results of virulence assay showed that the majority of Bacillus isolates showed slime formation (63.7%) and biofilm formation (84.7%).The prevalence of the hemolytic activity of Bacillus spp isolates showed the total β- hemolysis activity of Bacillus spp reached 77.4% while the α- hemolysis activity and γ– hemolysis reached 16.1% and 6.5%respectively. Bacillus spp isolates showed the total Lecithinase activity of Bacillus spp reached 53.2%. The prevalence of production of -amylase Bacillus spp isolates showed the total hydrolysis 87.1% and all isolates of Bacillus cereus having ability to starch hydrolysis except one isolates with 96.3%. The cytotoxic activity of 94 Bacillus spp isolates supernatant fluid indicated 100% cytopathic effect on the Vero cell line with different degree 46.8%, 41.5% and 11.7% for (+++), (++) and (+) respectively. The highest percentage of resistance against examined antimicrobial agents was recorded in penicillin 100%, resistance against Cephalothin, Oxacillin, Sulfamethazole /Trimethoprim, and Nalidixic acid were 95.2% 94.4%, 77.4%, and 62.9% respectively. for genotypic detection of different distribution of virulence factors gene of isolated Bacillus spp revealed that the amplification for CytK, nheA, nheB, nheC, plc, entFM, hblA, hblC and hblD gene were 58.9%, 33.9%, 13%, 25%,40.3%, 35.5%, 45.2%, 29.8% and 20% respectively. Each isolates regardless of their origin harbored at least one of the enterotoxin. genes indicating their pathogenic nature, which must be considered as serious health hazard.