Microbiology
What you must understand
Microbiology questions test organism identification, virulence and treatment. Build a classification framework: bacteria (Gram-positive vs Gram-negative, cocci vs bacilli, aerobes vs anaerobes), viruses (DNA vs RNA, enveloped vs non-enveloped), fungi (yeasts vs moulds), and parasites. Know the culture and staining characteristics, the toxins that drive disease (e.g., diphtheria toxin inhibits protein synthesis; cholera toxin raises cAMP), and the first-line antimicrobial for common pathogens. Understand sterilisation and disinfection, and the principles of infection control and immunisation.
Traps that appear in questions
- Confusing exotoxin (protein, heat-labile, toxoid vaccine possible) with endotoxin (lipopolysaccharide, heat-stable, causes fever and shock).
- Mixing up Gram stain results and the corresponding antibiotic coverage.
- Forgetting that viruses cannot be treated with antibacterials and that some (e.g., influenza) need antivirals.
- Overlooking notifiable diseases and post-exposure prophylaxis in public-health stems.
Worked example (rule of thumb)
A patient with a wound infection after soil contamination: suspect Clostridium tetani if there is muscle rigidity, or Clostridium perfringens if there is rapid tissue necrosis with gas. Both are Gram-positive, spore-forming, anaerobic bacilli. Rule of thumb: spore-formers in soil = Clostridium, and treatment includes debridement plus the appropriate antitoxin or antibiotic.
Exam strategy
For each organism, state Gram reaction, shape, oxygen requirement, toxin and drug of choice. That five-point template answers most microbiology questions.