Effect of subminimal inhibitory concentrations of pefloxacin on the piliation and adherence of E. coli.

Several recent reports have shown that sub-lethal concentrations of antibiotics may decrease the adhesive ability of bacteria to epithelial cells; however, the mechanism by which the antimicrobial agents reduce adherence has remained unknown. The effect of sub-MICs of pefloxacin, a new broad-spectrum antibacterial quinolone, was studied on: haemagglutination, adherence, outer membrane and fimbriae of a pyelonephritogenic E. coli strain. The strain agglutinated in a mannose-resistant way human P1 but not p erythrocytes. After purification, the fractions containing outer membrane and fimbriae proteins were studied using electron microscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The E. coli strain, grown in the presence of sub-MICs of pefloxacin, exhibited: (i) abnormal forms with filament formation; (ii) a markedly altered capacity of haemagglutination (human P1 erythrocytes) and adherence to uroepithelial cells. The inhibition of haemagglutination and adherence corresponded to a decrease in P-fimbriae production. These results were also associated with changes in the extraction of the outer membrane proteins of pefloxacin-treated bacteria. No major qualitative difference could be seen in outer membrane and P-fimbriae protein profiles after growth with sub-MICs of pefloxacin. This study has demonstrated that sub-lethal concentrations of pefloxacin alter piliation and the outer membrane of E. coli. These changes are associated with reduced bacterial haemagglutination and adherence.