Fig. 1. Effect of longeterm storage at freezing temperature on the viability of C. difficile spores. C. difficile spores of strains R20291 (filled squares) and M120 (filled triangles)
suspended in PBS buffer were incubated at 80 C (A) and 20 C (B) during 4 months. C. difficile spores of strains R20291 (empty squares) and M120 (empty circles) in meat were
incubated at 20 C during 2 months. Aliquots were plated onto BHI-YST agar plates, and colony forming units counted after anaerobic incubation for 36 h at 37 C. Results are the
average of three independent experiments. Bars represent standard error, too small to be visible for some data points when