By: Karen Crawford, Ph.D.
President, List Biological Laboratories, Inc.
You hear about Clostridium difficile at your doctor’s office and in news articles, but what does it mean and how does it affect the world around us?
C. Difficile Statisitcs
- C. Difficile Mortality Rates: Complications from C. difficile infection (CDI) have become an increasing patient safety concern worldwide (CDC). Mortality rates from C. difficile-associated disease have been increasing, from 5.7 deaths per million (1999) to 23.7 per million (2004) in the USA, which is higher than deaths caused from all other intestinal infectious diseases combined.
- Cost of Treating C. Diff: The cost of treating CDIs in the USA is estimated at over $3 billion per year.
- Increased Virulence of C. Difficile Strains: Hypervirulent C.difficile strains, toxinotype III and ribotype 027 (B1/NAP1) cause C. difficile infections with high rates of pseudomembranous colitis and mortality. Increased virulence of these strains relative to the classical strains has been attributed to a natural resistance to fluoroquinoline (McDonald, 2005), higher sporulation rates(Akerlund, 2008), production of a third toxin, binary toxin or C. difficile transferase (CDT) which adds to pathogenicity and enhances colonization(Schwan, 2009), and more efficient translocation of the toxin(Lanis, 2010).
- Widespread in All Types of Facilities: In 2012, the Centers for Disease Control and Prevention reported that CDI now affects all types of medical care facilities, including community care facilities such as retirement homes.
How C. Difficile Affects the Intestine
C. difficile enterotoxins A and B are the key to pathogenesis of CDI. C. difficile toxin A (TcdA) and toxin B (TcdB) are both cytotoxic and cause inflammation in intestine, but they have slightly different activities (Theriot, 2013). Toxin B is an extremely potent cytotoxin, that glycosylates small GTPase of the Rho family (Cdc42 and Rac) which control the actin cytoskeleton in eukaryotic host cells; this glycosylation disrupts signaling pathways of the cell cycle and lead to apoptosis. TcdA has an activity like TcdB, but it is much less potent as a cytotoxin, but more commonly noted for its enterotoxic activity and large size (308 kDa vs 270 kDa for TcdB). These toxins are the major virulence factors for C. difficile and cause inflammation and damage to cells in the intestine when the normal gut microflora are disrupted, such as after a round of treatment with antibiotics (Theriot, 2013; Carter, 2010).
Earlier studies using animal models of CDI had suggested that the toxins act synergistically because purified TcdA alone was able to induce C. difficile disease pathology and TcdB was not effective unless it was co-administered with TcdA. However, the isolation of some new, clinically relevant toxin A-negative, toxin B-positive (A−B+) strains of Clostridium difficile from humans (Drudy 2010), indicated that toxin B may be the key to its virulence as a pathogen (Lyras 2009, Carter 2010). The emergence of these new strains has prompted researchers to evaluate current C. difficile diagnostic methods (Alder 2014, Brown 2011, Garamella 2012, Grein 2014) and recommend ensuring that medical laboratories can detect both TcdA and TcdB in specimens.
List Labs Offers TcdA and TcdB for Purchase
List Biological Laboratories has been producing TcdA and TcdB since 2000. These toxins are purified proteins that are tested to ensure that the activity is preserved. Along with chicken antibodies to each toxin, TcdA and TcdB can be used in disease modeling as well as the development of diagnostic tools for CDI detection and diagnosis.
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