الفهرس 
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Abstract
Mastitis is one of the most important health problems of dairy cattle as it causes physical, chemical and bacteriological changes in the produced milk. A total of 480 different samples were collected from cows and their surrounding environment including 210 milk samples from apparently healthy cows, 60 milk samples from clinically mastitic cows, 60 teat swabs, 50 milking machines swabs, 50 worker’s hand swabs and 50 bedding samples from different farms containing small and large dairy herds located in El Dakhalia and Menoufiya Governorate. California mastitis test was carried out to detect subclinical mastitis in milk samples collected from apparently healthy cows, the prevalence of positive CMT was 60.48% (127/210). These samples were examined bacteriologically and biochemically for isolation and identification of mastitis causing bacteria. Our results revealed that the prevalence of E.coli was 33.33% (11/33), 21.74% (20/92), 16.67% (4/24), 18.52% (5/27), 13.33% (2/15) and 13.33% (4/30) in milk samples from clinically mastitic cows, milk samples from subclinically mastitic cows, teat swabs, milking machines swabs, worker’s hand swabs and bedding samples, respectively, while the prevalence of Staphylococcus aureus was 23.08% (9/39), 17.43% (19/109), 11.9% (5/42), 10.53% (4/38), 17.07% (7/41) and 10.53% (4/38), in the same groups respectively. The prevalence of Streptococcus agalactiae was 27.8%, 34.8%, 22.2%, 22.2%, 23.5% and 20.8% in milk samples collected from clinically mastitic cows, milk samples collected from subclinically mastitic cows, milking machines swabs, teat swabs, worker’s hand swabs and bedding samples, respectively, while, the prevalence of Streptococcus uberis was 22.2%, 17.4%, 38.9%, 37.04%, 47.06% and 37.5%, in the same groups, respectively. A significant variation of the number of these bacteria according to cows age, season, locality, herd size and hygienic condition of the farm was detected. Moreover, multiplex PCR was done on 14 isolates of E. coli for detection of ESBL producing E. coli. The results of PCR revealed that the prevalence of blaTEM and blaSHV was 64.3% (9/14) and 92.9% (13/14), respectively, while none of the isolates carried blaCMY-2. Conventional PCR was done on 28 isolates of Staph. aureus for detection of some genes responsible for antibiotic resistance. Our results revealed that the prevalence of bla (Z) was 14.3% (4/28).
Key words: Mastitis, E.coli, Staphylococcus aureus, Streptococcus agalactiae,
blaTEM, bla (Z).