Effects of subinhibitory concentrations of pefloxacin on the adherence of Staphylococcus aureus to human cells.

The adherence of bacterial strains to eukaryotic cells can be influenced by subinhibitory concentrations of antibiotics. The effect of sub- and infra-MICs of pefloxacin, a new broad-spectrum antibacterial quinolone, on the adherence of Staphylococcus aureus to human buccal cells, was studied. Six S. aureus strains belonging to several serotypes and all sensitive to pefloxacin were pretreated with serial twofold dilutions of the drug (from 1/2 to 1/1024 the MIC). After the adhesion test, 100 buccal cells were counted in randomly chosen microscopic fields using a Nomarski interference microscope and attachment was measured as the percentage of cells with at least 50 or more adhering bacteria. Sub-MICs (1/2 and 1/4 the MIC) of pefloxacin increased the diameter of the six staphylococci. All of the strains, grown in the presence of pefloxacin, exhibited a markedly altered capacity for adhesion to buccal cells. The highest significant decrease was observed for 1/2 to 1/8 the MIC, although infra-MICs such as 1/1024 the MIC also decreased the attachment of S. aureus to buccal cells. These results were compared with those obtained with other antibiotics active against S. aureus.