Covers Vibrio cholerae and Aeromonas hydrophila in turn. For cholera it sets out the organism's general features, a table of virulence factors, laboratory diagnosis, the stepwise pathogenesis through toxin action, clinical features, treatment and vaccines. For Aeromonas it outlines the general features, a table of pathogenic factors, the diseases it causes, diagnosis, antibiotic sensitivity and prevention.
Topic 61 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 3 sections, about 350 words (3 min of reading), with 14 flashcards.
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Vibrio cholerae and Aeromonas hydrophila
VIBRIO CHOLERAE
AEROMONAS HYDROPHILA
VIBRIO CHOLERAE
General Characteristics
Gram-negative, comma-shaped curved rods
Facultative anaerobes
Motile with a single polar flagellum
Oxidase-positive (distinguishes from enteric G-rods)
Non-spore forming
Grow well at alkaline pH (8.5–9.5) but are killed by acid
Ferment sucrose and mannose, not arabinose
Rapid growth on peptone water, blood agar, and TCBS agar (Thiosulfate Citrate Bile Salts Sucrose agar – shows yellow colonies due to sucrose fermentation)
Show polymorphic forms (S-shaped, filamentous, coccobacilli) in Pfeiffer stain
Virulence Factors of V. cholerae
Lab Diagnosis
Specimens: stool, vomit
Microscopy: Gram-negative curved rods, Pfeiffer stain shows "shooting star motility"
Culture: Grows rapidly on:
Peptone water
Blood agar
TCBS agar (yellow colonies due to sucrose fermentation)
Biochemical:
Indole (+)
Oxidase (+)
Serology: Gruber agglutination
Rapid diagnostic tests available (dipsticks, latex agglutination)
Pathogenesis of Cholera
1. Ingestion of contaminated food/water
2. Survival in stomach depends on pH – more likely with antacids
3. Colonization of small intestine via TCP
4. Cholera toxin production → B subunit binds GM1 ganglioside → A subunit activates adenylate cyclase → ↑cAMP → massive secretion of water & electrolytes
5. Results in: profuse watery diarrhea (“rice water stool”), severe dehydration
Clinical Features
Cholera (O1/O139):
Sudden onset of profuse watery diarrhea
Vomiting, dehydration
Muscle cramps, metabolic acidosis, hypokalemia
No fever typically
Milder gastroenteritis with non-O1/non-O139 strains
Treatment
Primary: Prompt rehydration therapy (oral or IV)
Antibiotics shorten duration:
Tetracycline, doxycycline
Alternative: azithromycin or ciprofloxacin
Prevention
Clean water supply, sanitation
Killed or oral cholera vaccine (Dukoral, Shanchol)
Public health measures during outbreaks
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