The major pathogen in Vibrio genus is Vibrio Cholerae. According to the O cell wall antigen, V. cholerae is divided into two groups.
They are O1 group and non-O1 group.
Organisms belongs to O1 group cause epidemic diseases.
Organisms belongs to non-O1 group cause sporadic diseases or they are nonpathogens.
There are three serotypes of cholerae as Ogawa, Inaba, and Hikojima.
According to the WHO estimations V. cholerae responsible for 120 000 deaths per annum worldwide.
Two serotypes Ogawa and Inaba cause epidemic cholera and Hikojima is rare.
cholerae is transmitted by the contamination of water and food with feces, primarily from human sources.
Human carriers who are in the incubation period or convalescent period are usually can be asymptomatic.
Marine shellfish such as Oysters and Shrimp are main animal reservoirs.
Ingestion of undercooked foods prepared by these marine shellfish can transmit the disease.
Watery diarrhea is the main clinical flinging of this infection.
Sudden onset of vomiting and large volumes of watery diarrhea can be seen in cholera.
There cannot be seen bloody diarrhea. Stool may appear like colorless, watery and with fishy odour, called as rice water stools.
There are no abdominal cramps. However, due to the loss of large volumes of body fluids patient may become dehydrated.
The loss of electrolytes and body fluids may cause hypovolemic shocks and may cause death in 12-24 hours. Without any treatment, the mortality rate is 40%.
Toxin production and pili are the major factors that affect the pathogenic mechanism.
Microscopy
Cholerae are Gram negative, usually curved rods (vibro). They are measuring 3-4 × 0.5 µm with a single flagellum.
They are motile organisms. Distinctive rapid to and- for movements can be seen. They can be seen under light microscope.
However, it is good to use a dark-field microscope.
Culture
This organism is an aerobe and facultative anaerobe. The optimal growth temperature is 37 ºC. However, they can grow over a wide temperature range of 16–40 ºC.
They grow well at alkaline pH 8.2. It is a non-halophilic organism. Culturing of stool is done for the diagnosis of this organism.
Alkaline peptone water
They grow rapidly on enrichment medium alkaline peptone water and produce turbidity on the medium and just below the surface of the medium.
Usually, they produce this turbidity within 4-6 hours.
Thiosulphate-citrate bile salt sucrose (TCBS) agar
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KIA media
On KIA media V. cholerae produces red slope, yellow butt. Gas is not produced and H2S also not produced by the V. cholerae
MacConkey agar
Produce small non lactose fermenting pale color colonies after overnight incubation as they are slow fermenters. When incubated prolonged, lactose fermentation can be seen.
This organism grows poorly or not at all on DCA and XLD agar
Blood agar
cholerae O1 and O139 grow on blood agar. Produce beta hemolytic colonies
TSI agar
An acid slant and acid butt is produced without gas and H2S.
Biochemical Tests
- Oxidase positive
- Urease negative
- ONPG test positive
- Indole positive
- VP variable according to the strain
- Mannitol, Glucose, Sucrose positive
- Lactose negative within 24 hours
- Citrate test, different strains give different results
- LDC (Lysine decarboxylase) test positive
Serotyping of V. cholerae can be done using antiserum.
Agglutination with polyvalent and monovalent antiserum can be use for serotyping the isolated organisms.
There is a rapid dipstick test to detect V. cholerae O1 and O139 in faecal specimens. It is an easy, cost effective procedure which used to identify the organisms in endemic areas.
The principle used here is immunochromatography.
There is a PCR assay to detect the hemolysins expressed by V. cholerae.
Treatment
The main treatment procedure is replacement of fluid and electrolytes.
These replacements and rehydrations can be done orally or intravenously according to the condition of the patient.
Tetracyclines, chloramphenicol and co-trimoxazole use to reduce the excretion of V. cholerae in the stool of patients.
To reduce the risk of environmental contamination and the cross- infections, Tetracycline is often used.
V. cholerae resistant to wide range of antibiotics including penicillins, streptomycin, chloramphenicol, sulphonamides and trimethoprim.
Prevention
Prevention can be mainly done by ensuring the supply of clean water and food to the public health. Moreover, it is necessary to dispose human faeces properly.
Vaccines composed of killed organisms has limited usefulness.
A live vaccine is also available in some countries. Tetracycline is useful for the prevention of the normal disease among close contacts.
Detection of carriers is very important to limit the outbreaks.
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