In the resistance induction procedure, there was a constant reduction in the sensitivity zone over each doubling of enrofloxacin concentration. The colonies found to be resistant at each concentration were sequenced. A comparison of the sequences of the colonies obtained at each step revealed that with respect to the initial E.coli ATCC25922 strain, resistance induction had resulted in a gyrB mutation at the Lys447 residue, which had been substituted for arginine