Description of the test
The pathogenic serogroups produce the cholera toxin, while the non-pathogenic strains may or may not produce this toxin.
The filamentous bacteriophage Ctx confers to the Vibrio cholerae (V. cholerae) strains the operon Ctx, containing the CtxA and CtxB. Transmission occurs by horizontal transfer, with integration of the operon into the bacterial genome, which then has the ability to produce the cholera toxin that confers pathogenicity in bacteria. This cholera toxin is responsible for symptoms of diarrhoea which poses a danger. As part of the NRC’s activities, a real-time PCR was developed to detect the virulent strains of V. cholerae (responsible for cholera) by targeting the Ctx operon (CtxA gene).
Amplification of the CtxA genes is done by real-time PCR.
Purpose of the assay
- Detection of the cholera toxin, the virulence factor of V. cholerae.
- Criteria for performing this test in the context of reference activities.
- All Vibrio strains received and confirmed as V. cholerae by the NRC and isolated from clinical samples.
Instructions for samples
Starting a culture of the V. cholerae strain from a fresh and pure subculture on a nutrient agar medium and shipped either on agar plate, deeply and mass inoculated in a nutrient agar tube, or on a swab in transport medium after scraping a subculture.
Instructions for transport
The strain should be shipped on the appropriate transport medium (agar plate, agar tube or swab with transport medium) and correctly labelled.
- Transport in triple packaging:
- agar plates and tubes hermetically tightly closed;
- packaging with adsorbent material in secondary packaging (transport case in blister pack, containers, etc.;
- the whole in a protective (padded) envelope or box.
- As soon as possible at room temperature, within 72 hours of preparation.
- Labelling and transport conditions in accordance with infectious agent regulations.
- For each strain, the application form (download on Sciensano’s NRC website) should be completed as fully as possible and sent with the strain.
Unacceptable requests
The following criteria are used to not accept the sample for analysis:
- unidentified sample
- application form incompletely completed,
- obvious storage and transport conditions not applied
- identification of V.cholerae not confirmed.
Turn around time (and frequency of analysis)
- Frequency of analysis: upon request.
- Time for detection: 48 hours.
- Days of analysis: every working day from Monday to Friday.
Reporting of test results
- How: reporting by telephone (1), paper by post (2) or electronically (3).
- When: if (even partial) relevant results of analyses are known (telephone, e-mail: 1 or 3), if all results of analyses are known (written report 2 or 3)
- Summary of all results available in the annual report