الفهرس 
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Abstract
In this study, 338milk samples collected from buffaloes were identified as 104 normal milk samples,148 subclinical mastitic milk samples and 86 clinical mastitic milk samples .While the total 48 cow’s milk samples were differentiated as 20 normal milk samples,18 subclinical mastitic milk samples and 10 clinical mastitic milk samples. Bacterial isolation and identification indicated that 88 and 6 coagulase negative staphylococci (CNS) isolates recovered from buffalo’s and cow’s milk samples respectively. We differentiate 94 isolates of CNS by API .Using the disc diffusion test for investigating the in vitro sensitivity of 94 CNS against 10 antimicrobial drugs revealed a resistance to Oxacillin, Ampicillin, Penicillin, Tetracycline, Vancomycin and Rifamin in an incidence of 46 (48.9%), 40 (42.6%), 30 (32%), 24 (25.5%), 8 (8.5%) and 4 (4.3%) respectively. Most of the CNS species were Congo red positive and constituted 66 isolates in a percentage 70.2%. Also testing the ability of CNS isolates to produce slime by Christensen’s tube (CT) method was done. Most of isolates showed absent and week degree constituted 42(44.7%) and 28 (29.8%) respectively, while both moderate and strong degrees constituted 12(12.8 %) of the isolates. It was obvious that the cytopathic effect of the isolates on MDCK cells were 100%in S. lugdunensis, S. sciuri, S.caprae, S. lentus, S. hyicus, S. chromogenes and S. xylosus to decrease to 80% in S. intermedius and S. epidermidis to the lowest percentage in S.hominis (60%).Using PCR, the 16s rRNA gene was detected in all the CNS while the nuc gene not expressed in all CNS species. For genotypic detection of six antibiotic resistance genes indicate that mec A gene was expressed in 58 isolates (61.7%) , blaz gene was expressed in 46 isolates (48.9%),tet K gene was expressed in 28 isolates (29.8% )while 100% negative amplification of tet M, tet O and tet L genes was observed in all the isolates of CNS .For genotypic detection of biofilm production from CNS species, the results revealed that ica D gene was (76.6%) and ica A gene was (13.8%).