الفهرس 
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Abstract
A total of 264 quarter milk samples from apparently healthy lactating cows were collected for detection and diagnosis of subclinical mastitis. Diagnosis of subclinical mastitis was performed by applying CMT, SCC test. Bacteriological examination was performed for isolation of S.aureus. Results revealed that S.aureus is the most important etiological microorganisms of subclinical bovine mastitis, and represent 31.5 % of subclinical mastitis and this results were confirmed by Coagulase test tube, Thermonuclease activity, and DNase test agar. Detection of S.aureus coagulase gene by PCR found to be sensitive and accurate method for identification of the isolates. Molecular evulation of S. aureus enterotoxines using muliplex PCR revealed presence of SEA, SEB, SEC, SED, and SEE respectively in (24.6 %, 33.4 %, 17.2 %, 26% and 14.7 %) of isolates. SDS were selected for study the severity of the cows response to the bacterial exosecretions four bands were detected between 36 and 31 kDa, where bands B and C present in most isolates.Purified S. aureus exosecretions injected in mice to understand an association between bacterial exosecretions and the severity of the cows’ response. Exposure of mice to a low bacterial dose of live homologous and heterologous S.aureus strains. This model assist to find S.aureus strains suitable for the development of vaccines against bovine mastitis caused by S.aureus, as well as more information for the understanding of the mammary gland immunity complex. Immunoblot tested present of S.aureus exosecretions antibodies and found some specific protein bands, blow the 36-kDa marker. ELISA tested the antibody levels against S.aureus exosecretions as antigens , antibodies were detected in all mice that were inoculated with the S .aureus exosecretions. Lymphocyte proliferation assays tested the role of S. aureus exosecretions for its ability to elicit in vitro proliferation of bovine blood lymphocytes and the results show that proliferation occur in most cases.