Medical Microbiology and Parasitology
What this domain tests
This domain tests sterilization and disinfection, culture media, staining, parasite identification and safe handling of infectious material.
Core rules
- Autoclaving uses saturated steam at 121°C and 15 psi for about 15 minutes. Air must be removed from the chamber, or the load will not reach temperature.
- Disinfection reduces pathogens on surfaces; sterilization kills all microorganisms including spores. Use the level of disinfection appropriate to the item.
- Culture media must be correctly prepared, pH-adjusted and sterility-checked. Blood agar, MacConkey agar and nutrient agar support different organisms.
- Gram staining separates bacteria into gram-positive purple and gram-negative pink. Ziehl-Neelsen staining detects acid-fast bacilli.
- For malaria, use a thick film to detect parasites and a thin film to identify species. Examine stool for cysts, ova and trophozoites.
- Perform antimicrobial susceptibility testing with a standardized inoculum and antibiotic discs; measure zones against a validated chart.
Worked example
An autoclave load shows a positive spore test despite the gauge reaching 121°C. Reasoning: trapped air can create a cool pocket, so the load is not sterile. Check air removal, loading pattern and door seal, repeat the cycle, and do not use the load until biological and chemical indicators pass.
Traps
- Treating autoclave tape as proof of sterilization.
- Using a thick film to identify malaria species.
- Reading antibiotic zones without a standard inoculum.
- Assuming all bacteria grow on ordinary nutrient agar.