Figure 1.

Effects of tigecycline on the growth, toxin gene expression and soluble toxin production of the historical C. difficile 9689 strain. (a) Antibiotic-free cultures; (b) 1/16× MIC (1.5 mg/L); (c) 1/8× MIC (3 mg/L); and (d) 1/4× MIC (6 mg/L). Tigecycline at the final concentrations indicated was added during early log phase growth (designated Time 0). Samples were collected in duplicate over 48 h for quantification of viable C. difficile, and for measurement of toxin gene expression by real-time RT–PCR and TcdA/B (Toxin AB) production by ELISA.The fold change in mRNA expression for each strain was calculated relative to that of its respective ‘no treatment’ control at 6 h (which was virtually zero).