FIG 3.

Test of development of resistance to cadazolid and comparator antibiotics by serial passages in liquid medium. C. difficile strains ATCC 9689 (a), NCTC 13366 (fluoroquinolone resistant) (b), and A-1290 (linezolid resistant) (c). Tubes containing 2 ml of 2-fold serial dilutions of the test antibiotics were inoculated with approximately 5 × 10⁶ to 2 × 10⁷ CFU. After incubation for 48 h at 37°C, the tube with the highest antibiotic concentration permitting growth was used to inoculate the next series of tubes (1%, vol/vol). This procedure was repeated for 13 passages, and the lowest antibiotic concentration inhibiting growth in the tubes (MICt) was recorded at the end of every passage.