Table of Contents
Diagnosis of Vibrio cholerae
Laboratory diagnosis of Vibrio cholerae; the bacteria responsible for cholera, and identifying the causative species, plays a great role in effective treatment and controlling outbreaks.
Here is the breakdown of what happens in the laboratory for Cholera to be confirmed.
Sample Collection
The first step in diagnosing cholera involves collecting stool samples from suspected patients.
Samples should be taken early in the course of the illness because that is when the bacterial load is highest.
But In cases where stool cannot be gotten, rectal swab is an alternative.
Also Water and food samples can be tested for the presence of Vibrio cholerae, especially in cases with risk of outbreak.
Culture Methods
The gold standard for diagnosing Vibrio cholerae is culture.
Commonly used culture media for Vibrio cholerae are
- Alkaline Peptone Water, an enrichment medium which is used for primary inoculation or as a transport medium.
- Thiosulfate-citrate-bile-sucrose (TCBS) agar, a selective medium.
The sample is inoculated into Alkaline peptone water (APW) or Thiosulfate-citrate-bile-sucrose (TCBS) agar.
As a selective media, TCBS encourages the growth of Vibrio cholerae, while inhibiting the growth of other bacteria.
After incubation, colonies are examined for characteristic features: Vibrio cholera ferments sucrose as a result, they form large, yellow colonies against the dark green agar of TCBS as shown in the picture below.
Microscopic Examination
Direct microscopic examination can also aid in diagnosis this includes:
- Gram staining: A smear is made from a colony on TCBS or from the Alkaline Peptone Water or directly from a stool sample. The smear is fixed and then stained.
Vibrio cholerae is a Gram-negative bacillus with “comma” shape.
- Phase contrast microscopy is used for wet preparation, to observe motility of the single flagellum Vibrio. This employs the hanging drop microscopy(the type of microscopy that uses a concave slide, for viewing motility of unstained organisms).
Molecular Techniques
Polymerase chain reaction (PCR) tests have been developed for rapid and sensitive detection of Vibrio cholerae. However, they are mainly used in research and water safety analysis especially in outbreaks, rather than in routine clinical diagnosis.
The strains of Vibrio cholerae most commonly associated with cholera outbreaks are primarily from the O1 and O139 serogroups.
With PCR, there is rapid identification and characterization of these strains during outbreaks, leading to faster intervention.
Rapid Diagnostic Tests (RDTs)
This is the conventional method used in primary health centers. Like most strip tests, they are based on antigen-antibody reactions, allowing for quick detection of Vibrio cholerae antigens in stool samples.
It is important to note, that while this method is fast and affordable, the specificity and sensitivity can vary. Cross reaction with other antibodies have been reported, therefore it might not stand alone in all cases.
Summary
To wrap this up I will summarize by saying this:
To fight cholera’s characteristic “Fast spread” we must use speed as well.
Fast symptom detection
Fast laboratory diagnosis and typing
Fast treatment
And Fast Control measures.
Reference
https://www.who.int/news-room/fact-sheets/detail/cholera
