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.
Organism Card
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| Lab discriminator |
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| Classic traps |
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Exam Intelligence
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GC 178 (An ugly wound): Animal bite wounds are a classic setting for Pasteurella multocida infection — the lecture emphasises wound infection pathogens and antiseptic technique; cat/dog bites are a core scenario [1].
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GC 105 (Medically important microbes): Pasteurella multocida is listed among medically important G−ve organisms every doctor should know — emphasised as the prototypical bite wound organism alongside Capnocytophaga [1].
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GC 106 (Practical issues in antibiotic use): Co-amoxiclav is the empirical antibiotic of choice for animal bite wounds — this is directly examinable as a prescribing question; the lecture warns against using cephalexin alone [1].
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GC 098 (Antibiotic prophylaxis): Cat bites warrant prophylactic antibiotics due to high infection rates (~50%) — the lecture frames prophylaxis indications by wound type, location, and host factors [1].
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AOS Microbiology material: Pasteurella is a "classic vignette" organism — very short stem required: animal bite + rapid-onset cellulitis = Pasteurella multocida [2].
- Onset timing is the key discriminator: Pasteurella causes infection within 12–24 hours of the bite. If the vignette says infection developed "3 days later" after a dog bite, consider Staphylococcus aureus, Streptococcus, or Capnocytophaga instead.
- Cat bite vs dog bite: Cat bites are deeper puncture wounds, higher inoculation → higher Pasteurella infection rate. Dog bites → broader polymicrobial flora, also risk of Capnocytophaga canimorsus.
- Asplenic patient + dog bite + fulminant sepsis = Capnocytophaga canimorsus (NOT Pasteurella — this is a common wrong answer).
- Cat scratch + regional lymphadenopathy (subacute, weeks) = Bartonella henselae (cat-scratch disease), NOT Pasteurella.
- Human bite + "clenched fist" injury = Eikenella corrodens, NOT Pasteurella.
- First-generation cephalosporin resistance: A favourite wrong-answer trap — students may choose cephalexin for "skin infection," but Pasteurella is intrinsically resistant. Always pick co-amoxiclav.
No directly relevant past paper questions concerning Pasteurella multocida were identified in the indexed Fourth Summative papers (2016–2025 MCQ, SAQ, and Minicase papers). The organism has not appeared as a named answer or stem pathogen in the available indexed past paper context.
However, note that the 2021 Fourth Summative SAQ Q12 [3] asks about organisms in immunocompromised settings (post-BMT), and the 2018 Fourth Summative Minicase [4] asks to name organisms causing specific infections — students should be prepared to list Pasteurella in any bite wound or soft tissue infection scenario if it appears in future papers.
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.
Brucella
Facultative intracellular, small Gram-negative coccobacillus transmitted from animals to humans, causing brucellosis—a systemic febrile illness characterized by undulant fever, hepatosplenomegaly, and osteoarticular complications.