Favourable effects of sub-MIC rufloxacin concentrations in decreasing the pathogen-host cell adhesion

The in vitro effects of sub-inhibitory concentrations of rufloxacin on Escherichia coli and Staphylococcus aureus adherence to human buccal epithelial cells were investigated. Epithelial cells were incubated with bacteria, grown in presence of serial dilutions of rufloxacin, from 1/2 MIC (Minimum Inhibitory Concentration) to 1/128 MIC. The mean number of bacteria adhering to cells and the percentage of cells bearing > or = 50 bacteria on their surface were counted and compared with those of controls (cells incubated with bacteria without rufloxacin). For both the bacterial strains tested, the maximal inhibition of bacterial adhesion occurred at 1/2 MIC concentrations. A lower, but statistically significant, inhibition was also observed with other sub-MIC concentrations up to 1/32 for both S. aureus and E. coli adhesion. These findings indicate that sub-inhibitory concentrations of rufloxacin, which may be present in vivo in the mucosae in the troughs of the dosage cycle, significantly inhibit the adhesive properties of bacteria involved in mucosal colonization.