الفهرس 
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Abstract
Combinations of antimicrobials are used widely to treat mixed infections, to overcome drug resistance and obtain greater antimicrobial effect from two or more drugs acting together “synergistic effect”. The combination between spiramycin (macrolid) and amikacin (aminoglycoside) has not been used in Egyptian veterinary field for treatment of mixed infection of mycoplasma and E.coli in broiler chickens. For this reason, the present study was carried out to detect certain antimicrobial effects of this combination in-vitro and in-vivo. The in-vitro sensitivity of E-coli to amikacin and an other common amtimicrobial drugs were done .
A- Antibacterial activity in–vitro
The sensitivity test is of a great value in recommendation of the effective antibacterial agents . Our results revealed that the tested isolate of E.coli was most sensitive to enrofloxacin, amikacin and gentamycin .
The present study demonstrated that MIC of enrofloxacin and amikacin were much lower than that of other antimicrobial drugs (gentamycin, doxycycline, chlorampheni¬col, ampicillin, sulfa /trimethoprim and colistin ).