Hi Aalaa,

The ciprofloxacin resistant Staph aureous GyrA gene had been found to be mutated at codon 84 (Ser to Leu) and codon 85 (Ser to Pro). These mutations are absent in the ciprofloxacin sensitive susceptible strains. Mutations of specific gyrase A residues close to a catalytic Tyr-122 (Ser 84 in S aureous) to hydrophobic residues Leu presumably disrupts the key interactions involving gyrase-quinoline complex.

For further reading I suggest the attached paper.

Hope that helps.

Thank u sir