The effect of quinolones on the intracellular killing of Staphylococcus aureus in neutrophil granulocytes

The effect of ciprofloxacin, lomefloxacin, fleroxacin and ofloxacin on the intracellular killing of Staphylococcus aureus in human neutrophil granulocytes was studied. Each drug was tested in concentrations of 0.25, 1, 4, 16 and 64 times the MIC and the intracellular killing was measured for up to 5 h of incubation. All four quinolones increased the intracellular killing in a concentration- and time-dependent manner. When compared at concentrations of 4 x MIC, ofloxacin increased the killing significantly more than the other quinolones. All four quinolones increased the killing significantly more than the beta-lactam dicloxacillin. All five antibiotics increased the killing significantly relative to the control without antibiotics. None of the antibiotics affected the viability of the granulocytes or their ability to generate superoxide anion. In conclusion, the quinolones increased the intracellular killing of S. aureus in neutrophil granulocytes.