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Toxin Detection Kits

Sector: Clinical

C. DIFFICILE TOXIN A TEST

Code: TD0970

C. difficile Toxin A Test is a rapid immunoassay for the direct qualitative detection of Clostridium difficile toxin A in faecal samples.

INTRODUCTION
Clostridium difficile is a Gram-positive anaerobic bacillus which has been identified as a common nosocomial pathogen that causes diarrhoea and pseudomembranous colitis associated with antibiotic therapy. In the 1960’s and 70’s, antibiotic associated pseudomembranous colitis became a major clinical problem, particularly due to the use of broad spectrum antibiotics such as ampicillin and cephalosporins. Larson et al (1977) reported that stool samples from affected patients contained a toxin that produced cytopathic changes in tissue culture cells1. Subsequently, C. difficile was identified as the organism responsible for toxin production2,3
C. difficile is known to produce at least two toxins, designated A and B.
Toxin A (mwt. 308 Kda) causes fluid secretion, mucosal damage and internal inflammation.
Toxin B (mwt. 250 Kda) is approximately 1000 fold more potent as a cytotoxin than toxin A, but is not enterotoxic4. It is therefore accepted that toxin A plays a more important role in the pathogenesis of C. difficile5.
Both toxins A and B are produced at the same time. The symptoms are primarily due to toxin A, but toxin B is thought to play a role in the disease by acting synergistically with toxin A6.
When established in the colon, C. difficile produces the toxins which cause diarrhoea and pseudomembranous colitis. C. difficile infection is almost exclusively a nosocomial infection. Outbreaks once established, are difficult to control and re-infection of patients is common.
Laboratory diagnosis depends on demonstrating the presence of C. difficile toxins in the stool sample. The most widely used test for detection of C. difficile toxin is cell cytotoxicity with neutralisation (using, for example, vero cells) which primarily detects toxin B7. This test takes up to 48 hours to obtain a result.
The Test Unit provides a rapid 30 minute method for the detection of C. difficile toxin A from patient samples, which is suitable for single or batch testing.
The Test Unit utilises a unique technology. The test is performed by addition of the sample to the absorbent pad in the Sample Window.
The absorbent pad incorporates a latex-labelled monoclonal antibody to Clostridium difficile toxin A. The pad is in contact with a test strip which contains regions of immobilised antibody.
To perform the test, the user delivers 125m ml of sample to the Sample Window, thus saturating the absorbent pad. The sample moves from the pad to the test strip, mobilising anti C. difficile toxin A mouse monoclonal antibody attached to blue latex beads present in the pad.
The sample, antibody-latex and C. difficile toxin A antibody-latex continues to move up the test strip to an immobilised region of anti C. difficile toxin A antibody.
The C. difficile toxin A attaches to the immobilised antibody and a blue line become visible in the Result Window.
As the sample continues to move up the test strip, it comes into contact with an immobilised strip of rabbit anti-mouse antibody, forming a blue line in the Control Window.

TEST PRINCIPLE
Clostridium difficile toxin A is extracted from faecal samples as described in ``Sample Preparation’’.
The Test Unit contains monoclonal antibodies to C. difficile toxin A.
The extracted antigen is added to the pad in the Sample Window. The pad contains blue latex labelled with antibody. The extract rehydrates the complex and, if present, the specific antigen reacts with the antibody.
The antibody-antigen-latex complex travels through the test strip by capillary action to an area midway along the Result Window. This area contains an immobilised line of monoclonal antibody to C. difficile toxin A.
A further reaction between the antigen-antibody-latex complex and the fixed antibody is shown by the formation of a blue line in the Result Window.
If no C. difficile toxin A is present no line will appear in the Result Window.

 
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