Bacterial Requirements & Virulence

X

Microbiology Reference Section

---

Culture Requirements

• Obligate Aerobes: Nocardia, Pseudomonas, Mycobacterium, Bacillus. (Nagging Pests Must Breathe).
• Obligate Anaerobes: Clostridium, Bacteroides, Fusobacterium, Actinomyces. (Can't Breathe Fresh Air). Lack catalase and superoxide dismutase.
• Satellite Phenomenon: H. influenzae needs NAD+ and Hemin. S. aureus provides NAD+ (Factor V) via hemolysis of blood agar.

Virulence Factors

• Protein A: S. aureus. Binds Fc region of IgG. Prevents opsonization and phagocytosis.
• IgA Protease: SHiN (S. pneumoniae, H. influenzae, Neisseria). Cleaves IgA to colonize respiratory mucosa.
• M Protein: Group A Strep. Molecular mimicry (tropomyosin). Antiphagocytic. Can cause rheumatic fever.

Enzymes & Pigments

• Coagulase: S. aureus (converts fibrinogen to fibrin, creating a clot shield).
• Urease: Proteus, Cryptococcus, H. pylori, Ureaplasma, Nocardia, Klebsiella, S. epidermidis, S. saprophyticus. (Pee CHUNKSS). Hydrolyzes urea to ammonia, raising pH.
• Pigments: Pseudomonas (Pyocyanin - blue-green), Serratia (red), S. aureus (gold), Actinomyces (yellow sulfur granules).

Capsules & Biofilms

• Biofilms: S. epidermidis (catheters), Viridans strep (dental plaques), P. aeruginosa (CF patients/contacts), nontypeable H. influenzae (otitis media).
• Capsules: Polysaccharide layer preventing phagocytosis. Identified by Quellung reaction.
• Encapsulated bugs: Pseudomonas, S. pneumoniae, H. influenzae type b, Neisseria, E. coli, Salmonella, Klebsiella, Group B Strep. (Please SHiNE my SKiS).