الفهرس 
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Abstract
Concern has been rising with the respect to the capability of clinically important bacteria to acquire resistance against antibiotics and disinfectants. The present study was carried out to investigate biosecurity status of examined dairy farms, prevalence of MRSA in examined dairy farms, risks factors associated with presence of MRSA, antimicrobial sensitivity of MRSA against commonly used antibiotics, antiseptics and disinfectants in veterinary field. Moreover, molecular identification of isolated S. aureus by duplex PCR of mecA and IS431 genes was conducted. 925 samples were collected divided into 744 animal samples inludes (372 individual milk and 372 teat swabs), 181 environmental samples include (36 bedding, 37 BTM, 27 feed troughs, 27 water troughs, 27 milk linear and 27 worker’s nasal swabs). MRSA were isolated and identified conventionally by culturing of collected samples on selective media, biochemical testing and cefoxitin disk diffusion test, while molecular identification undertaken on 70 S. aureus isolates represents different samples and farms. Besides, suspension test was performed to test selected disinfectants and antiseptics in different dilutions and contact times, also kirby-bauer test performed to test selected antibiotics. MRSA recovered from total collected samples at rate 22.4% and from isolated S. aureus at rate of 37.7%, there is significant difference between MRSA isolated from different sources, according to CMT observation MRSA isolated from 41.4% mastitic milk followed by 31.6% from subclinically mastitic milk, then 17.6% from normal milk the difference was significant. Regarding to seasonal variation MRSA isolated in summer higher than the rest seasons. Molecularly, out of 70 isolates MRSA were detected in 24 isolates at percent 40%. According to antimicrobial sensitivity Ciprofloxacin and Trimethoprim- sulfamethoxazole antibiotics showed marked sensitivity on MRSA isolates, as well as iodine and Q.A.C. work effectively on tested MRSA isolates. Concerning risk factors, higher prevalence in cattle milk and farm environment reflecting a continuous state of presence of various sources of infection in dairy cattle farms including; animal and environmental reservoirs that could transmit MRSA regularly to cattle. Also, the higher prevalence in dairy cattle farms may be traced back to inadequate hygienic measures applied in these farms with unwise use of antibiotics as well as inadequate personal hygiene of farm workers. Moreover, the higher prevalence of MRSA among farms observed in this study may reflect lacking of record keeping, applying routine culturing and antibiotic sensitivity, un-restricted access of visitors and presence of veterinary supervision.