text: Resistance to fluoroquinolones is common in staphylococcus and pseudomonas. Resistance occurs in multiple ways. One mechanism is by an alteration in topoisomerase IV enzyme. A double mutant form of S. pneumoniae Gyr A + Par C bearing Ser-81-->Phe and Ser-79-->Phe mutations were eight to sixteen times less responsive to ciprofloxacin.