Fig 1. Formation of rough and smooth colonies by multiple C. difficile strains.

C. difficile strains representing five different ribotypes (indicated in parentheses) were grown on BHIS agar medium for 72 hours to allow differentiation of colony morphology. Growth was recovered and plated on BHIS agar for visualization of individual colonies. Shown are representative images from two independent experiments. Black triangles indicate smooth colonies, and white triangles indicate rough colonies. All images were taken at ×2 magnification. ATCC, American Type Culture Collection; BHIS, brain heart infusion plus yeast.