Ultrastructure of Clostridium difficile colonies

• First report on Clostridium difficile colony ultrastructure.
• In young cultures great intracolony variability is present.
• Invasive C. difficile cells were detected.

The ultrastructural colony architecture of six Clostridium difficile strains belonging to four different ribotypes (001, 027, 078/126 and 036) was studied by scanning electron microscopy (SEM). In 2-day-old colonies several microareas differing in cell length and organization could be differentiated. Some cells at colony edges were extremely long and exhibited invasiveness into the agar. The ultrastructure of 5-day-old colonies is more homogenous and characterized by presence of sporulating cells, spores and extracellular matrix.