Abstract
Bacterial mastitis is one of the most important diseases in high-production dairy cows which causing high economic losses. Staph. aureus and E. coli considered most common mastitis-causing bacterial pathogens. Therefore, 120 mastitis milk samples were collected from mastitic cattle to identify the profile of bacterial pathogens especially Staph. aureus and E. coli, in addition, studying their antimicrobial resistance. The obtained results revealed that incidence of Staph. aureus from examined mastitis milk samples was 45% (36/80) as single culture and 12.5% (10/80) as mixed culture. Incidence of E. coli from mastitis milk as a single culture was 30% (24/80) and as a mixed culture was 16.25% (13/80). In addition, out 16 samples as mixed infections summarized as following: 7 samples Staph. aureus with E. coli and 3 samples Staph. aureus with streptococcal species and 6 samples E. coli with streptococcal. Regarding to antimicrobial susceptibility, Staph. aureus was sensitive to tetracycline 41.6% followed by sulfa-trimethoprim 38.3% while E. coli strains were sensitive to tetracycline 50 % followed by Gentamycin 25%, both strains were resistant to marbofloxacin at rate 55.5 and 83.3%, respectively. Virulence genes including 23S rRNA, phoA related to specie-specific for Staph. aureus and E. coli in addition antibiotic resistant genes mecA and ampC, respectively were detected in 100% of examined strains. Detection of virulence and antibiotic resistance genes may be helpful for effective control of mastitis.

Key words: Mastitis milk, E. coli, Staphylococcus aureus, antibiotic resistance genes