Different groups of antibiotics (quinolones, macrolides, penicillin and cephalosporins) were chosen and used in this study. These antibiotics included ciprofloxacin, erythromycin, amoxycillin, cephalexin and cephradine respectively. Twenty six bacterial species were collected from urine, milk, rectal swabs, liver, wounds, intestine and also from isolated culture which were supplied by the department of microbiology, faculty of veterinary medicine, university of Khartoum, Sudan. Identification was done by using identification kits namely Quick GN "Nissui" and also by using biochemical tests as confirmatory tests. The bacterial species were found to be: Klebsiella pneumonaie, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and six strains of Salmonella species. Sensitivity tests were performed for all these organisms against various antibiotics with different concentrations using standard disk diffusion method. Ciprofloxacin was found to be the most effective drug against all the organisms tested even at a very low concentration (0.781 µg /ml), all the Gram-negative bacteria were found to be resistant to erythromycin. Pseudomonas aeruginosa strains were found to be highly sensitive to ciprofloxacin and resistant to the most of the other groups of antibiotics. Quinolon group (Ciprofloxacin, ofloxacin and pefloxacin) was found to be the most effective group against Salmonella typhi

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Mastitis is the most important disease in dairy farms worldwide causing significant economic losses. Sixty milk samples were collected from mastitic cows and submitted to the laboratory for further bacteriological examinations, Staphylococcus spp. (45%), Bacillus spp. (22.5%), Enterobacter spp. (14.5%), Pseudomonas spp. (8%), Acinobacter spp (5%) and Micrococcus spp (5%) were found in bacteriological examination of all milk samples. Staphylococcus aureus was the most prevalent among Staphylococci isolates (45%), followed by Staphylococcus intermedius (22%), Staphylococcus warneri (11%), Staphylococcus hyicus (11%), Staphylococcus chromogenes (11%) and Staphylococcus lentus (11%) Also Bacillus spp were found to be: Bacillus alvei (40%) Bacillus thermophilus (20%), Bacillus coagulans (20%) and Bacillus firmus (20%). Sensitivity tests were conducted using 12 different antibiotics including Tetracycline and Gentamicin. The sensitivity was determined for each antibiotic by using disc diffusion technique according to Kirby-Bauer method. The isolated bacteria were highly sensitive to Ciprofloxacin, Ifovluxtsen, Linezolid, Gentamicin and they were found to be resistant to Cloxacillin, Cephalexin, followed by Tetracycline, Lincomycin. Roxithromycin. This study showed that the most causative agent of mastitis in south Khartoum is Staphylococcus aureus. Hygienic practices procedure in dairy farm must be sustainable to reduce this disease and to be aware about the suitable antibiotics to be used using antibiotic sensitivity test. The present study was designed to investigate the sensitivity of different antibiotics against bacteria isolated from suspected mastitic cows in dairy farms in south Khartoum, Sudan.