Construction of a gyrA plasmid for genetic characterization of fluoroquinolone-resistant Staphylococcus aureus.

We have constructed a gyrA trans-complementation plasmid, pAT512, by cloning the wild-type gyrA gene of Staphylococcus aureus into the expression vector pAT392. Introduction by electrotransformation of pAT512 into a high-level fluoroquinolone resistant mutant of S. aureus (ciprofloxacin MIC = 16 micrograms ml-1) having a gyrA mutation which results in a Ser-84 to Leu substitution, reduced the MICs of norfloxacin and ciprofloxacin for the host of four- and eight-fold, respectively.