Clostridium difficile toxin DNA
Detection of toxigenic Clostridium difficile DNA
Indications for Testing
In-patients with healthcare associated acquired diarrhea in a patient with prior or concurrent antibiotic exposure
Special Instructions and Forms
C. difficile associated diarrhea is a Provincial Notifiable Disease.
Loop-mediated isothermal DNA amplification (LAMP).
C. difficile toxin DNA
Clostridium difficile associated diarrhea
Clostridium difficile infection
Antibiotic associated diarrhea
Unpreserved stool: Unformed (diarrhea) in sterile screw cap container.
Cary-Blair-preserved stool: Unformed (diarrhea) in Cary-Blair screw cap collection container.
Specimen Minimum Volume
|Cary-Blair Preserved stool||NO||YES*||YES|
* Refrigerate up to 5 days, if longer delay anticipated freeze.
Reject Due To
|Formed stool||Not consistent with CDAD|
|Preservative other than||Cary-Blair|
|Positive test within previous 14 days||Not a test of cure|
|≥ 3 negative tests in preceding 7 days||Consider alternative diagnosis|
Detection of toxigenic C. difficile in hospitalized, institutionalized or community patients with diarrhea and demonstrated current or recent antibiotic exposure.
C. difficile, the major cause of antibiotic-associated pseudomembranous colitis, is also the most frequently identified cause of hospital-acquired diarrhea. C. difficile is present asymptomatically as part of the bowel microbiota in up to half of all healthy neonates during the first year of life; the carriage rate decreases to the adult rate of ≤ 3% by the age of 2. Many antibiotics and anticancer drugs disrupt the bowel microbiota sufficiently for C. difficile to proliferate and precipitate disease. In addition, C. difficile may become problematic in patients with bowel stasis and those who had bowel surgery. The clinical manifestations of CDAD (C. difficiles associated diarrhea) range from a self-limiting diarrheal disease that disappears when antibiotics are discontinued to fulminant presentations with characteristic pseudomembranes within the large intestine and progression to toxic megacolon, bowel perforation and death.
The genus Clostridium comprises obligately anaerobic rods that usually stain Gram-positive in young cultures. Clostridium species are widespread in the environment partly due to their ability to form resistant endospores. They are found in soil, feces, sewage, and marine sediments. C. difficile has been isolated from various natural habitats and the feces of domestic animals and humans. Outbreaks in hospital-acquired C. difficile enteric infections are often traceable to environmental sources and other typical background factors for nosocomial infection. Toxigenic and nontoxigenic strains exist in the environment. Only toxigenic strains are associated with clinical disease. Two large toxin proteins (TcdA [or toxin A] and TcdB [toxin B]) are thought to be the primary virulence factors of C. difficile. These toxins are encoded by two separate genes, named tcdA and tcdB, respectively. Together, with three additional genes, they form a 19.6kb pathogenicity locus called PaLoc. Nontoxigenic strains lack PaLoc.
C. diffile toxin DNA DETECTED:
Presence of toxigenic C. difficile.
Due to asymptomatic colonization, particularly for those ≤ 2 years old, clinical signs, symptoms and risk factors should be considered.
C. difficile toxin DNA NOT DETECTED:
No toxigenc C. difficile. A negative test cannot be used to exclude CDAD. If clinical signs, symptoms and risk factors are inconsistent with result consider
submission of repeat specimen.
C. difficile toxin INDETERMINATE:
Specimen submitted contained substances inhibitory to test. Please submit a recollected specimen to complete investigation.
Johnson, E. A., Summanen, P., and Finegold, S. M. 2007. Clostridium, p. 889-909. In Murray, P. R., Baron, E. J., Jorgensen, J. H., Landry, M. L., and Pfaller, M. A. Manual of Clinical Microbiology, 9th ed., vol. 2. ASM Press, American Society for Microbiology, Washington, DC.
Meridian Biosciences Inc. 2011. Illumigene C. difficile: Package insert. Meridian Biosciences Inc. Cincinnati, OH.
Onderdonk, A. B., and Garrett, W. S. 2010. Gas Gangrene and Other Clostridium-Associated Diseases, p. 3103-3109. In Mandell, D., Bennett, J. E., and Dolin, R. Principles and practice of infectious diseases, 7th ed., vol. 2. Churchill Livingstone, Elsevier, Philadelphia, PA.
Loop-mediated DNA amplification (LAMP)
|Status||Days||Analytic Time||Maximum Laboratory Time||Specimen Retention|
|Routine||Monday – Friday||Same day||24h||1 week|
The illumigene® C. difficile DNA molecular assay is based on loop-mediated amplification technology, which uses specifically designed primers to the PaLoc pathogenicity locus to provide for specific and continuous isothermal DNA amplification. A by-product of this amplification is the formation of magnesium pyrophosphate, which forms a white precipitate leading to a turbid reaction solution. This presence of turbidity signifies a positive reaction while the absence of turbidity represents a negative reaction. The illumigene® C. difficile assay contains primers that specifically amplify a 204 bp
region of the conserved 5’ sequence of the tcdA gene within the PaLoc of toxigenic C. difficile in diarrheal stool samples from patients suspected of having C. difficile-associated disease.
Performing Laboratory Location
Newfoundland & Labrador Public Health Laboratory