الفهرس 
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Abstract
This study aimed to identify the profile of bacterial pathogens linked to clinical bovine mastitis in dairy cows including (Staph. aureus, E. coli and others bacteria) in addition, studying their virulence and antimicrobial resistance genes of Staph. aureus and E. coli isolates. Therefore, A total of 120 mastitic milk samples were collected under a septic condition from cattle and buffaloes showing signs of mastitis. All samples were subjected to bacteriological examination at Animal Health Research Institute, Damanhour branch. The following results were obtained:
Out of the 120 examined mastitic milk samples 80 samples were positive for bacterial isolation while 40 samples were negative for isolation.
Incidence of Staph. aureus from examined mastitic milk samples was 45% (36/80) as single culture and 12.5% (10/80) as mixed culture.
Incidence of E. coli from mastitic milk as a single culture was 30% (24/80) and as a mixed culture was 16.25% (13/80).
Incidence rate of Pseudomonas aeruginosa from mastitic milk was 5% (4/80).
Out 16 samples as mixed infections summarized as following: 7 samples Staph. aureus with E. coli and 3 samples Staph. aureus with Strept. and 6 samples E. coli with Strept.
The antimicrobial susceptibility test of 36 Staph. aureus isolates from mastitic milk showed that 41.6 % were resistant to tetracycline, 38.8% were resistant sulfa-trimethoprim and 33.3% were resistant to cefquinome. Whereas 55.5% of the tested strains were sensitive to marbofloxacin, Florfenicol 50% and amoxycillin 41.6%.
The antimicrobial susceptibility test of 24 E. coli isolates from mastitic milk showed that 50 % were resistant to tetracycline and Gentamycin 25%. Whereas 83.3% of the tested strains were sensitive to marbofloxacin, Florfenicol 50% and amoxycillin 50%.
Species-specific gene (23S rRNA) and antibiotic resistance gene (mecA) was detected in 100% of examined staph. aureus isolates from mastitic milk.
species-specific gene of E. coli (phoA) and antibiotic resistance gene (ampC) was detected in 100% of examined E. coli isolates from mastitic milk.