FIG. 1.

Effects of subinhibitory concentrations of ampicillin (A), clindamycin (B), ofloxacin (C), and moxifloxacin (D) on the expression of C. difficile colonization factor-encoding genes in four NAP1/027 strains: one moxifloxacin susceptible (strain CD196) and three moxifloxacin resistant (strains 6296, 6425, and CD07-259). Bacteria were grown overnight in medium supplemented with 0.5× MIC of antibiotic. The data are the mean relative expression ratios (expression in bacteria grown with antibiotic versus expression in control grown in antibiotic-free medium) ± standard deviations. The dotted line represents the threshold value of upregulation (threefold).