Medical Microbiology and Infectious Disease
Bacterial structure and pathogenesis
Know the differences between Gram-positive (thick peptidoglycan, teichoic acid) and Gram-negative (thin peptidoglycan, outer membrane, lipopolysaccharide) organisms. Endotoxin is LPS and drives septic shock via TLR4; exotoxins are secreted proteins with specific actions (e.g. diphtheria toxin inhibits EF-2, cholera toxin raises cAMP, tetanospasmin blocks inhibitory neurotransmitters). Understand virulence factors: capsules (antiphagocytic), pili (adhesion), and siderophores (iron acquisition).
Virology and mycology
Distinguish DNA and RNA viruses, enveloped versus non-enveloped, and replication strategies. Know that influenza undergoes antigenic shift (reassortment) and drift (point mutation). HIV targets CD4 T cells via gp120 and CCR5/CXCR4. Herpesviruses establish latency. Fungal infections are common in neutropenia (Aspergillus, Candida) and T-cell deficiency (Pneumocystis, Cryptococcus).
Diagnostics and antimicrobials
Understand culture, Gram stain, PCR, serology, and antigen testing. Know mechanisms of resistance: beta-lactamases, MRSA via altered penicillin-binding protein, vancomycin resistance via altered cell wall precursors, and efflux pumps. Sterilisation versus disinfection and the principles of infection control are examinable.
Traps
Do not attribute endotoxin activity to Gram-positive organisms. Know that antibiotics do not treat viral infections and that viral latency explains recurrence. Antibody presence may indicate past exposure rather than active infection; IgM suggests recent infection but has exceptions (e.g. reinfection, cross-reactivity).
Rule of thumb
Match the toxin to its mechanism: diphtheria = EF-2 inhibition; cholera = cAMP increase; tetanus = inhibitory neurotransmitter blockade; botulinum = acetylcholine release blockade.