الفهرس 
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Abstract
In this study a total of 20 and 78 milk samples were collected from animals showed clinical and sub clinical mastitis criteria respectivelyintended for isolation and identification of different pathogens causing clinical and subclinical mastitisin some dairy farms of Beni-Suef Governorate, and investigation of their in vitro sensitivity. The most prevalent microorganisms recovered were Staphylococcal species (no=79, 80.61%) followed by Enterococcus spp. (n=28,28.57% ),Pseudomonasaeruginosa ( n=7 , 7.14%),CAMP negative Streptococci (n=6, 6.12%),E.coli (n=3 ,3.06%) and Proteus vulgaris (n=1, 1.02%).
Staphylococcal species (no=79, 80.61%) were characterized as coagulase- negative staphylococci (n=45, 45.92%), Staphylococcus aureus (n=23, 23.47%) and Staphylococcus intermedius (n=11, 11.22%).
The in-vitro sensitivity tests revealed thatall isolates of S. aureus were sensitive to vancomycin(100%) and the majority of isolates showed high sensitivitytociprofloxacin,doxycycline(73.9%)Followedbygentamicin(69.5%),rifampicin(60.86%),cefoxitin(52.17%). On the contrary, S.aureus isolates were highly resistant to penicillin(82.6%) followed by cefoxitin (47.8%) and spectinomycin(21.7%).
All S. aureusisolates which were resistant to penicillin and cefoxitin are phenotypically considered as MRSA. Therefore, out of 23 tested isolates, 11 were categorized phenotypically as MRSA in a percentage of 47.83%.
Multi drug resistance (MDR) was detected amongst 6 isolates (26.09%). The corresponding values for S. intermedius were vancomycin (100%),gentamicin(72.73%), ciprofloxacin, doxycycline, rifampicin(63.64%)followedbycefoxitin(54.54%) on the contrary S.intermedius isolates were highly resistant to penicillin(90.91%) followed by spectinomycin(27.28%).while results showed that the majority of coagulase- negative Staphylococci were highly sensitive to vancomycin (100%)followed by ciprofloxacin,gentamicin(73.33%),doxycycline and cefoxitin(62.22%).On the other side coagulase- negative staphylococci isolates were highly resistant to penicillin (82.22%) and rifampicin(77.78%) followed by spectinomycin(40%) . Multi drug resistance (MDR) was detected amongst 16 isolates (35.55%).
The majority of Streptococcus isolates highly sensitive to ampicillin, ciprofloxacin, vancomycin(66.66%) followed by doxycycline(50%)and gentamicin(33.33%) On the contrary streptococcus isolates were highly resistant to erythromycin (50%). While, the majority of Enterococcus spp. were highly sensitive to doxycycline (67.86%)in the other hand isolates were highly resistant to ampicillin,gentamicin(50%),vancomycin(46.42%), ciprofloxacin (39.28%).With lower resistant to erythromycin (17.85%).Multi drug resistance (MDR) was detected amongst 4 isolates (14.28%).
All isolates of E.coli No(3)and Proteus vulgaris NO(1) showed sensitivity (100%) towards amoxicillin-clavulanic acid, aztreonamm , cefotaxime, cefoxitin ciprofloxacin, ceftazidime, cefepime, doxycline , gentamicin and trimethoprim-sulfamethoxazole .
While all isolates of Pseudomonasaeruginosa No(7) showed senstivity (100%) to ciprofloxacin, ceftazidime, cefepime, colistin,doxycline and gentamicin On the contrary all the isolates showed resistant(100%) to amoxicillin-clavulanic acid aztreonamm , cefotaxime, cefoxitin and trimethoprim-sulfamethoxazole. All isolates showed multiple drug resistance(MDR).
All the recovered S.aureus isolates were seeded on Congo red agar media to detect their biofilm forming ability. All the tested isolates showed biofilm forming ability either strong or intermediate. 13(56.52%) of them were strong biofilm producer, while 10 (43.48%) were intermediate biofilm producer. Genotypic detection of some biofilm associated genes (icaA, icaD and bap genes) for 19 out of 23 isolates of S.aureus showed that only two isolates(10.53%) out of 19 were negative for all the tested genes, 16 isolates (84.21%) harbored both icaA and icaD gene while only one isolates harbored all the tested genes (5.26%).
All the recovered S.aureus and CNSisolates were seeded also on blood agar to detect their hemolytic activity and results showed that the highest prevalence of α-hemolytic activity (narrow zone of incomplete hemolysis) was detected amongst CNS (64.44%) while the highest prevalence of ᵦ - hemolytic activity (wide zone of complete hemolysis) was detected amongst S. aureus isolates (82.61%).