Sub-minimum inhibitory concentrations of ceftibuten reduce adherence of Escherichia coli to human cells and induces formation of long filaments

The minimal inhibitory concentrations (MICs) of an antibiotic are present for only a certain period of time, after which they become sub-inhibitory concentrations (sub-MICs). These sub-MICs are still active because they can interfere with the mechanism of bacterial adhesion, which is the first step in the sequence of events leading to infection. The purpose of the present study was to investigate the effects of sub-MICs of ceftibuten, a new third-generation cephalosporin, on the adhesion of Escherichia coli (E. coli) to human buccal cells. The degree of inhibition was maxima1 at 1/2 MIC and then gradually returned to the control values at 1/128 the MIC. The differences were statistically significant from 1/2 to 1/32 MIC. Since the MIC was 0.5 μg/ml, concentrations from 0.25 to 0.015 μg/ml significantly reduce bacterial adhesion. Ceftibuten also caused marked elongation of E. coli. These findings could help to explain the efficacy showed by ceftibuten in the treatment of respiratory and urinary tract infections when administered once daily.