Effect of subinhibitory concentrations of ceftazidime, ciprofloxacin, and azithromycin on the hemagglutination and adherence of uropathogenic Escherichia coli strains.

The effect of subinhibitory concentrations (sub-MICs) of ceftazidime, ciprofloxacin, and azithromycin on the hemagglutination (HA) and adherence ability of 29 P-fimbriated Escherichia coli strains to the buffalo green monkey kidney (BGMK) cell line was investigated. Comparisons were made between the values of HA titer before and those after exposure of strains to 1/2, 1/4, 1/8, 1/16 and 1/32 MIC of antibiotics, as well as between the number of bacteria attached to the BGMK cells before and the number after their exposure to the same concentrations of antibiotics. Azithromycin at concentrations of 1/2 and 1/4 MIC damaged the HA capacity of the studied strains, while ceftazidime at concentrations of 1/2, 1/4, 1/8 and 1/16 MIC and ciprofloxacin at concentrations of 1/2 and 1/4 MIC increased the HA capacity of P-fimbriated E. coli. All three antibiotics decreased the adhesive capacity of E. coli to the BGMK cells. Comparing the number of adhered bacteria before and after exposure to sub-MICs of antibiotics, statistically significant differences were determined (p < 0.01) after exposure of the strains to all the concentrations of ceftazidime used after exposure to 1/2, 1/4, 1/8 and 1/16 MIC of ciprofloxacin, and after exposure to 1/2, 1/4 and 1/8 MIC of azithromycin. Filaments formed by sub-MICs of ceftazidime and ciprofloxacin in a static experimental system caused HA, but in an experimental system imitating in vivo conditions, the strains adhered poorly to the cells.