الفهرس 
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Abstract
S.aureus is recognized worldwide as a pathogen causing intramammary infections in dairy cows and thus of economic significance to dairy farms, as it reduces milk quality and production. It has been found responsible for more than 80% of subclinical bovine mastitis, which may result in about $300 loss per animal (Wilson et al. 1997 & Dego et al. 2002).
So this research based on detection best tests to early detection S.aureus mastitic infection.
224 milk samples (146 clinical mastitic milk samples & 78 subclinical mastitic milk samples) were randomly collected from different small holder farms, firstly all were tested by CMT, as 155/224 (69.2%) sample were positive to CMT.
Subclinical mastitic milk samples 29/78 (37.17%) were positive to CMT, for further identification samples were undergone to conventional methods of isolation and identification as follow : cultivated on selective media to S.aureus as only 21/29 (72.41%) were positive producing S.aureus colonies, then directed to staphylococcal biochemical tests as only 16/21 (76.19) were positive S.aureus, followed by cultivation on blood sheep agar as 9/16 (56.25%) were positive haemolysin production. Number of sample produced slime layer production 13/16 (81.25%) were positive, and thermo-nuclease production 9/16 (56.25%) were positive. (7) isolates were selected randomly of surely positive subclinical S.aureus mastitis were subjected for gene-typical characterization for the presence of coagulase genes by PCR assay using oligo-nucleotide primers that amplified genes encoding coagulase (Coa) gene and m-PCR for detection S.aureus enterotoxin genes.The results of PCR assay revealed that (7) isolates of S.aureus were positive for coagulase gene while only one of them reveled present of enterotoxin-D gene.
On the other hand clinical mastitic milk samples 126/146 (86.3%) were positive to CMT, for further identification samples were undergone to conventional methods of isolation and identification as follow : cultivated on selective media to S.aureus as only 41/126 (32.54%) were positive producing S.aureus colonies, then directed to staphylococcal biochemical tests as only 17/41 (41.46%) were positive S.aureus, followed by cultivation on blood sheep agar as 16/17 (94.11%) were positive haemolysin production. Number of sample produced slime layer production 8/17 (47%) were positive, and thermo-nuclease production 4/17 (23.53%) were positive. Randomly, chosen (3) isolates of surely positive subclinical S.aureus mastitis were subjected for gene-typical characterization for the presence of coagulase genes by PCR assay using oligo-nucleotide primers that amplified genes encoding coagulase (Coa) gene and m-PCR for detection S.aureus enterotoxin genes. The results of PCR assay revealed that (3) isolates of S.aureus were positive for coagulase gene while all negative to enterotoxin genes primers.
The present study was carried out to study the presence of some virulence factors genes in S.aureus as slime layer, coagulase, haemolysin, thermo-nuclease, enterotoxin production.
Isolates from dairy sub-clinical mastitis which is very important prerequisites for implementation of effective control programs to face the economic losses due to subclinical mastitis caused by this microorganism and detection the best antibiotic used during dry phase .
S.aureus isolates were sensitive to different antibiotic discs recorded in the present study as follow 100% for gentamycin and cephradine, 94.7% for norofloxacin, 84.2% for vancomycin, 68.4% for cloxacillin and kanamycin, 57.9% for trimethoprim/sulphamethoxazol, 36.8% for amoxicillin, 31.6% for penicillin, 15.8% for lincomycin, 15.7% for cefotaxime, 5.3% for ampicillin.