For resistance induction, and initial bacterial suspension of E.coli ATCC 25922 was prepared at a concentration of 0.5McFarland. This was sown onto 50brain infusion both agar (Becton Dickinson, StLouis, Missouri) dishes using a calibrated 10μl loop and aerobically incubated at 37°C for 18h to 24h. The resulting colonies were then diluted in brain infusion broth (Becton Dickinson, StLouis,Missouri)and sown on brain infusion agar (Becton Dickinson, StLouis, Missouri) with an initial enrofloxacin concentration of 0.008μg/ml, which was doubled up at each step to 655.36μg/ml (11thstep, T11) in which resistant strains were obtained