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.

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.

Virulence 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

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.