The effects of quinolones on the adherence of type-1 fimbriated Escherichia coli to mannosylated agarose beads.

Abstract

Bacterial adherence is reported to be antagonized by several classes of antibiotics including quinolones, beta-lactams and tetracyclines, based primarily on in-vitro studies in which bacterial cells are exposed to antimicrobials, incubated in the presence of uroepithelial cells (UECs) and assessed for adherence by light microscopy. Some problems associated with the use of this approach, include low sensitivity, high variability and, in the case of adherence of mannose-sensitive Escherichia coli interference by mannose-containing uromucoid. To avoid these problems, mannosylated agarose beads (MABs) were used as a model for UECs. Adherence of E. coli strain AAEC356, which is constitutive for type-1 fimbrial expression, was maximal with 3 x 10(4) beads/mL and 1 x 10(8) bacterial cells/mL co-incubated for 35 min at 37 degrees C. Those bacterial cultures showed 40-60% adherence to MABs but only 4-10% adherence to UECs. This study reports a novel method to detect mannose-sensitive bacterial adherence, using MABs, in order to determine the effects of quinolones, cefdinir and tetracycline on E. coli adherence. Cefdinir and the quinolones ciprofloxacin, enoxacin and PD131628 caused significant reductions in the adherence of AAEC356 to UECs at concentrations equivalent to 1/2 x MIC, while up to 1 x MIC of these antibiotics had no significant effect on adherence to MABs. A direct comparison of UEC to MAB-based techniques showed that PD131628, at concentrations equivalent to 1/16x, 1/4x, 1/2x and 1 x MIC, had no effect on bacterial adherence to MABs, while reductions of 34%, 38%, 87% and 85% respectively were seen in adherence to UECs. The anti-adherent effect mediated by quinolones may not therefore be related to the specific interaction between type-1 fimbriae and mannosylated receptors. While quinolones and cefdinir had no effect on overall bacterial adherence to MABs, there was a decrease in the ability of alpha-methyl-D-mannoside (alpha-MM) to inhibit competitively this adherence. Concurrent exposure of PD131628 or cefdinir with tetracycline prevented this, suggesting that protein synthesis is required for this effect.