الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
A total of 415 lactating Holstein cows from different localities in Delta area, Egypt including 345 cows from four dairy farms at Damietta (farm A, 60 lactating cows, farm B, 65 lactating cows and farm C, 120 lactating cows) and El-Sharkia (farm D, 100 lactating cows) Governorates in addition to 70 individual cases of dairy cows at El-Dakahlia Governorate; were examined for clinical and subclinical mastitis during the period from October 2014 to June 2018. Concerning to the prevalence rate of clinical and subclinical mastitis, it was found that the overall prevalence of mastitis in this study was 224 (54%) at the cattle level, 50 (12%) were clinical and 174 (42%) were subclinical cases. The prevalence rate at the quarter level was 467 (52.1%), 106 (11.8%) were clinical and 361 (40.3%) were subclinical. All the potential risk factors considered in the present study namely, season of the year, hygienic measures and age of the cow affected prevalence of mastitis. from etiological point of view, the current bacteriological examinations revealed that CNS were the predominant bacteria isolated from mastitic cases (32%) followed by, E. coli (24.8%), S. aureus (15.4%), Str. agalactiae (13.4%), Str. dysgalactiae (8.8%), E. faecalis (2%), Str. uberis (2%), Enterobacter aerogenes (0.66%), Micrococcus (0.66%), Enterobacter agglomerans (0.22%) and Klebsiella spp. (0.22%).In the present study, the results of antibiotic sensitivity test for Staphylococcus spp. revealed that oxacillin was the most resistant antibiotic (92%), followed by ampicillin (90%), cefoxitin (86%), cefotaxime (70%), tetracycline (70%), ampicillin/sulbactam (64%), sulphamethoxazole/trimethoprim (64%), erythromycin (58%), gentamicin (50%), ofloxacin (42%), chloramphenicol (40%), ciprofloxacin (34%) and vancomycin (2%).In respect to using PCR for confirmation of Staphylococcal infections, the nuc gene and coa genes were used for confirmation of the isolated S. aureus. Results revealed that all the recovered S. aureus harbored the amplified products of both genes. On the other hand, the tuf gene was used for confirmation of CNS species where all of them were positive for this gene. Regarding to the prevalence of antibiotic resistance genes of Staphylococci spp., the obtained results revealed that all of the 25 Staphylococcal isolates were found to be positive for the presence of mecA (100%) and 24/25 isolates were positive for the presence of blaZ gene (96%) where 19/25 isolates were phenotypically resistant to β-lactam antibiotics, 3/25 expressed intermediate resistant phenotype for ampicillin and also, 3/25 were intermediate resistant for oxacillin. Detection of tetK gene in 17/25 isolates (68%) where 15/17 were resistant phenotypically to tetracycline, one isolate was intermediate resistant and one isolate was sensitive to tetracycline although carrying tetK gene. Only 6/25 isolates were positive for the presence of fexA gene (24%) where three isolates were phenotypically resistant to chloramphenicol, one isolate was intermediate resistant and two isolates were sensitive although carrying fexA gene.