V.cholerae

Question 1

Classification

Answer 1

Family: vibrionaceae
Genus: vibrio
Species: cholerae

Question 2

Morphology

Answer 2

Gram negative comma shaped rods

Actively motile by means of a single polar flagellum

On prolonged cultivation, vibrios may become straight rods that resemble the gram- negative enteric bacteria

Question 3

Growth characteristics

Answer 3

• facultatively anaerobic
• non-fastidious
• temperature range of 14 - 40oC (37oC optimum)
• grows better in alkaline medium
• ferments sucrose
• ferment lactose and glucose
• Oxidase positive (key preliminary identification of V.cholerae from other vibrios)

Question 4

Antigenic structure

Answer 4

• Heat-labile flagella H antigen
• somatic O antigen (LPS) -> serologic specific
  At least 206 O antigen groups
• V.cholera serogroups O1 and O139 cause classic cholera
• occasionally non 01/ non 0139 V.cholerae cause cholera like disease

Question 5

Virulence factors

Answer 5

• Motility
• adherence: tcp (toxin coregulated pili)
• enterotoxins: heat-labile cholera toxin (hypersecretion of water and electrolytes)
• neuraminidase

Question 6

Disease

Answer 6

Cholera

Pathogenesis: activates the gs pathway which leads to activation of cAMP—> lead to perfused water secretion into the intestine

Clinical presentation:

Sudden onset of nausea, vomiting and watery diarrhea in large volumes - “rice water” stool; no abdominal pain

Profound dehydration may lead to shock, cardiac and renal failure

Question 7

Microbiological diagnosis

Answer 7

Specimen

• vomitus
• stool mucous flecks

DME

• hang drop mount: to observe motility
• gram stained smear: gram neg. rod with “c” or “s” or comma-like forms predominating
• IFA

Cultures
- alkaline peptone water: subcultures to TCBS agar or AA (alkaline agar) are made within 6 to 12 hrs
- alkaline agar (AA)
- thiosulfate-citrate-bile sucrose (TCBS) agar:
Yellow colonies

Specific test: 
Oxidase-positive colonies are further identified by:
- biochemical tests
- rapid slide agglutination tests 
- specific gamma bacteriophages

• indole positive due to presence of red colour
• ferment glucose and lactose

Serologic diagnosis:
Tube dilution agglutination test

Question 8

Treatment and prevention

Answer 8

• water and electrolyte replacement
• tetracyclines or quinolones are empirical agents of choice

Prevention:

Nonspecific - public health measures that ensure a clean water and food supply

Specific - killed vaccine has limited usefulness