Abstract
A total of 10Staphylococcusaureusisolates were recovered from 117 milk samples which were obtained from 93 dairy cows indifferent farms suffered from clinical mastitis, these isolates were phenotypically characterized and identified based on colony morphology andbiochemical tests. In addition, antibiotic susceptibility pattern of these strains was investigated and a trial to investigate the mechanism of the isolated bacterium to antibiotic resistance by PCR detection of class 1 integron. The milk samples were examined bacteriologically: Thirty-three out of 117 samples (28.2%) were positive for staphylococcus. Ten out of 33 samples (30.3%) were coagulase positive staphylococcus. The S. aureus isolates were highly sensitive to Cephalothin (DF30), Ampicillin/sulbactam (SAM), Methicillin(DP5µg), Amoxicillin-Clavulanic acid (AMC30) and Trimethoprime-Sulphamethaxole (SXT25µg), Susceptibility rates of S. aureus to these antibiotics were: 90, 80, 80, 70 and70%, respectively. Higher resistance was observed to Streptomycin (S10µg), Kanamycine (K30µg), Tetracycline (Te30µg), Erythromycin (E15µg), Cefotasime (CTX30µg), Cefoperazone (CFP75µg), Ampicillin (AMP10µg), Gentamycine (GN10µg), Amoxicillin (AX25µg) and Ciprofloxacin(CIP5µg), Susceptibility rates of S. aureus to these antibiotics were: 30, 30, 30, 30, 40, 40, 40, 40,40 and 50%, respectively. The molecular detection of S. aureus specific sequence gene(Sa), genes encoding clumping factor A (clfA), gene encoding S. aureus protein A (spa)and the class 1 integron using Polymerase Chain Reaction were carried out. A total of 10 Staphylococcus aureus isolates were negative for the presence of class 1 integron but yielded an amplicon size of about107 bp in case of S. aureus specific sequence gene (Sa), an amplicon size of about 638bp in case ofclfA gene. Amplification of the(spa) gene encoding S. aureus protein A was detected in 9 strains out of 10 (90%)and yielded an amplicon size of about 226bp. The data in this study provided an overview on the incidence of staphylococcus aureus in clinical mastitis and the distribution of virulence determinants and antibiotic resistance of these S. aureus strains.

Key words: Molecular detection, class 1 integron,(Sa), clfA, (spa),S.aureus isolates, mastitic cows