Effect of sparfloxacin on Staphylococcus aureus adhesiveness and phagocytosis

We investigated the effect of sparfloxacin, a new broad-spectrum fluoroquinolone, on the morphology, adhesiveness and phagocytosis of a clinical isolate of Staphylococcus aureus sensitive to this compound (MIC = 0.06 mg/L). The strain was tested for its adherence to human buccal epithelial cells, measured by interference contrast microscopy, and for phagocytosis by guinea-pig peritoneal macrophages, measured by fluorescence microscopy. Accumulation of sparfloxacin by macrophages was studied by means of a velocity-gradient centrifugation technique. The S. aureus strain, grown in the presence of sub-inhibitory concentrations of sparfloxacin, exhibited an increased cell diameter and a markedly reduced capacity to adhere to buccal epithelial cells. The phagocytic capacity and activity of macrophages were greater with the treated strain than with an untreated control. A reduction in numbers of intracellular cocci was also observed 2 h after postphagocytic treatment of macrophages with sparfloxacin at 10 x MIC. This intracellular bactericidal activity may result from accumulation of sparfloxacin in macrophages, evidenced by a high ratio of cellular to extracellular concentration. It was concluded that sparfloxacin reduces adherence to epithelial cells, increases phagocytosis and facilitates the intracellular killing of S. aureus.