Effect of Subinhibitory Concentrations of Ciprofloxacin and Gentamicin on the Adherence of Pseudomonas aeruginosa to Vero Cells and Voided Uroepithelial Cells

The effect of subinhibitory concentrations (1/8 x, 1/16 x, 1/32 x MIC) of ciprofloxacin or gentamicin on the adherence of Pseudomonas aeruginosa to Vero cells and voided uroepithelial cells was studied using two different assay methods. Strains studied included both reference strains and clinical strains, including mucoid and nonmucoid isolates. Sub-MICs of ciprofloxacin decreased adherence to Vero cells and voided uroepithelial cells in 3 of 4 ciprofloxacin-susceptible nonmucoid isolates but not in ciprofloxacin-resistant or mucoid isolates. Sub-MICs of gentamicin significantly reduced adherence in 5 of 7 nonmucoid strains but not in mucoid strains. Gentamicin effect on adherence did not correlate with susceptibility to ciprofloxacin. We conclude that ciprofloxacin susceptibility determines the effect of sub-MICs of ciprofloxacin on P. aeruginosa adherence to Vero cells and voided uroepithelial cells. In addition, both the Vero cell assay and voided uroepithelial cell assay demonstrated similar results.