RESUMEN
Twenty-five bacterial samples were isolated from buffalo faeces. Twenty strains out of twenty -five strains were identified as Escherichia coli. Antibiotic susceptibility tests and plasmid analysis carried on the E.coli isolates. Antibiotic susceptibility tests of the isolated strains of E. coli were done by antibiotic disc diffusion method. The antibacterial agents were ampicillin, amoxicillin, neomycin, kanamycin, streptomycin, tetracycline, nalidixic acid, flumequine, erythromycin and enrofloxacin. Plasmid DNAs were extracted from each of the drug resistant E.coli strains. All of the collected E.coli strains were resistant to ampicillin, amoxicillin, neomycin, kanamycin, streptomycin, tetracycline, nalidixic acid, flumequine, erythromycin and enrofloxacin at 90,80,100,50,100,75,75,60,100 and 35% respectively. From the results it was revealed that molecular size of the plasmid DNAs extracted from twenty different drug resistant E.coli varied from 9.162 to 13.000 Kb. In this investigation it was revealed that each of the twenty drug resistant E.coli harbored a single plasmid. It can be said that increasing incidence of drug resistance in E.coli to different antibiotics including the broad spectrum antibiotics tetracycline, nalidixic acid and. heralds the coming therapeutic problem in the treatment of infections cause by this micro-organism