Clostridium difficile (etymology and pronunciation), also known as C. difficile, C. diff (/siː/ /dɪf/), or sometimes CDF/cdf, is a species of Gram-positive spore-forming bacteria.Clostridia (members of the genus Clostridium) are anaerobic, motile bacteria, ubiquitous in nature, and especially prevalent in soil. Under the microscope, they appear as long, irregular (often drumstick- or spindle-shaped) cells with a bulge at their terminal ends. Under Gram staining, C.