الفهرس 
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Abstract
840 milk samples from 220 lactating buffaloes with previous history of mastitis were examined for detection of recurrent clinical and subclinical mastitis, the clinical mastitis prevalence rates were 25.55% in Sharkia and 29.23% in Dakahlia governorates. The incidence of subclinical mastitis was 40% and 33.84% in Sharkia and Dakahlia governorates. E. coli was isolated from 63 (18.47%) mastitic milk samples out of 341 examined ones. 63 E. coli isolates were serotyped to O157, O153, O55, O18, O114, O126, O26, O1 and 21 untyped strains. Virulence tests were performed on E. coli serogroups isolated from mastitic cases. It was found 50 strains (79.37%) were serum resistant, 24 (38.1%) had Congo red binding activity, 20 (31.75%) were invasive and 8 (12.7%) had haemolytic activity. PCR was applied to detect the presence of stx2 and eaeA genes, stx2 was found in all strains tested while eaeA gene was found in 3 E. coli strains. Electrophoretic profiles of 10 E. coli isolates whole membrane protein gave 32 to 37 discrete bands with molecular weight ranged from 11.9 to 130.3 kDa.