Effect of subinhibitory antimicrobial concentrations (sub-MICs) on in-vitro bacterial adherence to uroepithelial cells.

Subinhibitory antimicrobial concentrations have been reported to alter the adherence of bacteria to uroepithelial cells. Most investigators assessing the influence of subinhibitory antimicrobial concentrations on bacterial adherence in the urinary tract have employed in-vitro techniques using voided uroepithelial cells. These cells are incubated with bacteria previously exposed to antimicrobials and adherence is assessed by light microscopy. Most investigators have studied urinary Escherichia coli isolates. beta-Lactams, tetracyclines, aminoglycosides, nitrofurantoin, chloramphenicol, quinolones, trimethoprim and sulphonamides have been studied in concentrations ranging from 1/32-1/2x MIC. The following effects of subinhibitory antimicrobial concentrations on bacterial adherence have been reported: penicillins consistently reduce bacterial adherence at concentrations 1/4-1/2x MIC; nitrofurantoin and chloramphenicol demonstrate variable effects on bacterial adherence at 1/4x MIC; tetracyclines, but not doxycycline, decrease adherence at high concentrations (1/4-1/2x MIC) and increase it at low concentrations (1/8-1/32x MIC); both trimethoprim and sulphonamides consistently decrease bacterial adherence at concentrations ranging from 1/32-1/2x MIC and 1/4-1/2x MIC, respectively, but it is unclear whether the combination of trimethoprim and a sulphonamide decreases bacterial adherence to a greater extent than either agent alone; aminoglycosides decrease adherence at 1/2x MIC; and quinolones decrease adherence at 1/4x MIC, with variable effects at 1/8x MIC and 1/16x MIC. Subinhibitory antimicrobial concentrations may exert their antiadhesive effects through suppression of formation and/or expression on the surface adhesin, the formation of functionally aberrant adhesins, or a direct effect on the bacterial surface. Presently, the clinical significance of the alterations in bacterial adherence to uroepithelial cells is not fully understood.