FIG. 2.
Numbers of untreated CFU, spores, and heat-resistant CFU of C. difficile 630Δerm and C. difficile R20291 after 5 days of incubation. Following 5 days of anaerobic incubation at 37°C in BHIS broth, the numbers of heat-resistant CFU were determined. Spore titers were determined by counting spores by phase-contrast microscopy using a Bright-Line hemocytometer (Sigma, United Kingdom). The bars indicate the averages of three independent experiments, and the error bars indicate standard errors of the means. The detection limit for colony counts was 50 CFU/ml, and the detection limit for spore counts was 1.6 × 103 spores.