Vibrio vulnificus
Halophilic, lactose-fermenting, curved Gram-negative rod found in warm saltwater that causes rapidly progressive wound infections and fulminant primary septicemia, especially in patients with liver disease or iron-overload states.
Organism Card
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Exam Intelligence
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GC 105 ("Medically important microbes") and GC 178 ("An ugly wound") both frame V. vulnificus as a key cause of necrotising soft tissue infection (NSTI) alongside S. pyogenes and polymicrobial causes [1]. The exam commonly presents a vignette of an immunocompromised patient with wound infection after seafood handling or seawater exposure.
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Maksim Surgery Notes explicitly list V. vulnificus alongside S. pyogenes and polymicrobial organisms as causes of necrotising fasciitis — with hallmark features of pain out of proportion, haemorrhagic bullae, systemic toxicity, and "dirty dishwater" discharge [3]. Know that LRINEC score > 8 = high risk, and finger probe test positivity indicates NF.
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The classic HKUMed vignette: middle-aged man with known hepatitis B cirrhosis (or alcoholic liver disease) presents with fever, shock, and haemorrhagic bullae on the lower limbs hours after eating raw oysters → V. vulnificus primary septicaemia. This ties directly to the "Jaundice after raw oysters" lecture block [2].
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TCBS agar colony colour is a favourite discriminator: V. vulnificus = green; V. cholerae = yellow. Both are oxidase-positive curved G−ve rods, so colony colour on TCBS is the rapid lab differentiator.
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Iron-overload connection: V. vulnificus has siderophore-independent iron uptake, making patients with haemochromatosis, thalassaemia major, or cirrhosis (high serum iron/transferrin saturation) uniquely susceptible. This is a common MCQ trap — the question asks "which underlying condition predisposes to fatal V. vulnificus septicaemia?"
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Treatment principle for NF: the exam expects "aggressive surgical debridement + IV broad-spectrum antibiotics" as a paired answer. For V. vulnificus specifically, the recommended combination is a 3rd-gen cephalosporin + doxycycline/tetracycline [1][3].
- V. vulnificus vs V. parahaemolyticus: V. parahaemolyticus causes self-limited gastroenteritis from undercooked seafood (Kanagawa phenomenon — β-haemolysis on Wagatsuma agar); it does NOT cause the fulminant septicaemia/NF picture. If the stem mentions liver disease + bullae → V. vulnificus, not parahaemolyticus.
- V. vulnificus vs Aeromonas hydrophila: both can cause wound infections from contaminated water, but Aeromonas is associated with freshwater, while V. vulnificus is associated with warm seawater/brackish water.
- "Pain out of proportion": this phrase in a vignette points to either necrotising fasciitis or gas gangrene. Differentiate by exposure history (seawater/seafood = V. vulnificus; post-trauma/surgery + gas on XR = C. perfringens) and the presence/absence of neutrophilia (absent in C. perfringens due to leucocidin) [3].
- Common wrong answer trap: selecting V. cholerae when the stem describes septicaemia with bullae. V. cholerae causes cholera (watery diarrhoea), not septicaemia or skin lesions.
No directly indexed past paper questions specifically naming or stem-matching Vibrio vulnificus were identified in the provided 2016–2025 Fourth Summative MCQ, SAQ, or Minicase papers. However, NF-related surgical vignettes (as per the Maksim Surgery Notes framing tested in past surgical SAQs) commonly draw on V. vulnificus as a key differential. Students should be prepared for this organism to appear in any stem involving:
- Raw oyster ingestion + liver disease + septicaemia
- Seawater wound + haemorrhagic bullae + NF
- LRINEC score interpretation
[1] Lecture slides: GC 105. Medically important microbes what every doctor should know.pdf; GC 178. An ugly wound Wound healing; Wound infection; Anti-septic technique.pdf [2] Lecture slides: Block A - Jaundice after raw oysters_ acute hepatitis.pdf [3] Senior notes: Maksim Surgery Notes.pdf (Necrotising fasciitis section, p.274–275)
Vibrio cholerae
Curved, oxidase-positive Gram-negative rod (serogroups O1 and O139) that produces cholera toxin, causing profuse secretory ("rice-water") diarrhea and potentially fatal dehydration.
Pasteurella multocida
Gram-negative coccobacillus predominantly transmitted through animal bites and scratches, causing rapidly progressive soft-tissue infections, and less commonly pneumonia, septicemia, or meningitis.