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Microbiology — Buzzwords — USMLE Step 2 CK Notes
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Toxin mechanisms
| Organism | Toxin action |
|---|---|
| Corynebacterium diphtheriae | Inactivates EF-2 |
| Pseudomonas (exotoxin A) | Inactivates EF-2 |
| Vibrio cholerae | Activates Gs → ↑cAMP |
| Bordetella pertussis | Inactivates Gi → ↑cAMP |
| Clostridium botulinum | Blocks ACh release (flaccid) |
| Clostridium tetani | Blocks glycine/GABA (spastic) |
| Shiga / Shiga-like | Inactivates 60S ribosome |
Encapsulated organisms (asplenia risk)
Mnemonic — Some Killers Have Nice Shiny Bodies: Streptococcus pneumoniae, Klebsiella, Haemophilus influenzae, Neisseria, Salmonella, group B Strep. These require opsonisation, so asplenic patients need vaccination and prompt treatment.
Classic stains and media
- India ink / capsule → Cryptococcus
- Silver stain → Pneumocystis, fungi, H. pylori
- Chocolate agar with factors V and X → Haemophilus
- Charcoal yeast extract with cysteine and iron → Legionella
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