Microbiology, Parasitology and Infection Control
What this domain tests
This domain tests basic microbiology and parasitology: staining, culture media, common pathogens, malaria and stool parasites, sterilization, standard precautions, and biomedical waste segregation.
Core rules
- Gram stain uses crystal violet, iodine, decolorizer, and safranin. Gram-positive organisms retain purple; Gram-negative organisms appear pink.
- Ziehl-Neelsen stain detects acid-fast bacilli as red, beaded rods on a blue background. A positive smear supports but does not alone confirm TB; NAAT is used for confirmation and resistance testing.
- For malaria, the thick film is more sensitive for detection; the thin film allows species identification. Report according to the programme format.
- Stool examination for ova and parasites requires fresh or properly preserved samples; multiple samples may be needed.
- Standard precautions apply to all patients: hand hygiene, gloves, gown, mask, eye protection, safe injection, and safe waste handling.
- Autoclaving at 121°C and 15 psi for 15 minutes is standard for steam sterilization. Alcohol does not reliably kill spores.
Worked example
A sputum smear after ZN staining shows red, beaded bacilli on a blue background. The MPHW-lab technician should report the smear as acid-fast bacilli seen and ensure the sample is sent for NAAT. The reasoning is that ZN staining is a screening method; molecular testing identifies Mycobacterium tuberculosis and detects resistance markers.
Traps
Do not call a Gram stain definitive species identification. Do not use a thick film for species identification. Do not place all waste in yellow bags; follow the colour code. Do not skip hand hygiene before gloves. Do not treat alcohol as a sporicide.