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The page below is a sample from the LabCE course Multi-drug Resistant Organisms: MRSA, VRE, and Clostridium difficile. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Stool Culture

Stool culture is very effective in detecting C. difficile. Unfortunately, non-toxigenic strains will also grow, requiring strains to be tested for toxin production.
The greatest disadvantage to culture is the length of time that is needed before results are available, which may be up to four days. However, antibiotic sensitivity testing following culture is useful for strain-typing that would provide necessary epidemiological information during nosocomial outbreaks.
Colonies of C. difficile will appear white, flat, and spreading on blood agar (see top image on the right). Cycloserin-cefoxitin-fructose agar (CCFA) is a selective media that is used for isolation of C. difficile. There is however, no distinction between pathogenic and commensal strains, which all produce yellow colonies with a characteristic "ground glass" appearance, as shown in the bottom image on the right. The characteristic odor of "horse manure" aids in identification of C. difficile. Stool samples are directly inoculated onto CCFA and incubated in an anaerobic atmosphere at 37°C for 48 hours.
Large gram-positive bacilli with spores will be observed on a Gram stain of a typical colony, as shown below.