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Vibrio

Vibrio is a genus of curved, comma-shaped, non-encapsulated, gram- negative facultative rods with shooting-star motility. Vibrio cholerae is responsible for causing cholera.

Scanning electron microscope image of Vibrio cholerae bacteria
Scanning electron microscope image of Vibrio cholerae bacteria

Vibrio cholerae

Pathogenesis

Route of entry
•    Fecal contamination of water and food
•    Animal reservoirs are shrimps and oysters
•    Carriers are usually asymptomatic

Somatic antigen and flagella antigen are present. A large number of bacteria, i.e. 1 billion, are required for colonization as are sensitive to hydrochloric acid in stomach. Pathogenesis depends on colonization of the small intestine by the organism and secretion of enterotoxin.

•    Vibrio attaches to the cells of the brush border of the gut, with aid of bacterial enzyme, mucinase.
•    Mucinase dissolves the protective glycoprotein coating over the intestinal cells.
•    After attachment, the bacteria multiply and secrete enterotoxin, choleragen. Choleragen consist of 2 subunits, ‘A’ inserted into cytosol and ‘B’ binds ganglioside receptor on the surface of the enterocytes.
•    ‘A’ submit catalyses the addition of ADP- ribose to the G protein, thus stimulating G protein.

Vibrio pathogenesisVirulence Factors

•    Pili
•    Enterotoxin
•    Mucinase

Predisposing factors

•    Over crowded place
•    Undercooked seafood
•    Poor hygiene
•    Lake of clean drinking water
•    Malnutrition
•    Inadequate  medical services

Lab Diagnosis

Specimen
For stool culture, blair or transport medium should be used.

Microscopy

Important microscopic features include:

•    Curved, comma-shaped
•    Gram- negative rods
•    Shooting-star  motility
•    Non-encapsulated
•    Facultative

Transmission electron microsope image of Vibrio cholerae
Transmission electron microsope image of Vibrio cholerae

Culture
•    Non-halophilic, like low concentration of Na+ ions.
•    Alkaline peptone water, turbidity on and just below the surface of the medium appears, within 4-6 hours.
•    Thiosulphate-citrate bile salt sucrose (TCBS) agar, yellow colonies are formed.
•    MacConkey agar, most strains are able to grow, giving cloudless colonies.
•    Blood agar, beta-hemolytic colonies are formed.

Biochemical Tests

Triple sugar iron (TSI) agar
Acidic slant and acidic butt is produced. No gas or H2S is formed.

•    Oxidase          Positive
•    Catalase         Positive
•    Ferments       Sucrose, Glucose, Mannitol
•    Urease            Negative
•    B. Galactosidase         Positive
•    Lactose                         Not fermented in 24 hours
•    Indole Test                  Positive
•    Lysine decarboxylase         Positive

Serological Tests
•    Rapid dipstick test
•    PCR

Clinical symptoms of Cholera

•    Rice water stools, containing

  • Mucous
  • Epitheloid cells
  • Large number of vibrios

•    Severe dehydration
•    Acidosis
•    Hypokalemia
•    Vomiting
•    Restlessness
•    Sunken eyes
•    Dry mucus membrane
•    Loss of skin elasticity

Vibrio Parahaemolyticus

Vibrio parahaemolyticus is a marine organism transmitted by ingestion of undercooked seafood. It has unknown pathogenesis, but enterotoxin is similar to choleragen. It is also halophilic.

Clinical symptoms

  • Mild to severe watery diarrhea
  • Nausea
  • Vomiting
  • Abdominal cramps
  • Fever

Biochemical tests are similar to V. cholera, except it does not ferment sucrose.

Vibrio vulnificus

Vibrio vulnificus is a marine organism, found in warm salt waters. It causes cellulities, especially in shellfish handlers. It causes rapid fatal septicemia in immune-compromised people eating raw fish containing the organism.
It produces hemorrhagic bullae on the skin as well. Chronic liver disease is a predisposing factor.
Doxycycline is given for treatment.

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