Laboratory Practice, Safety and Applied Skills
Domain 11 tests safe laboratory behaviour, aseptic technique and core applied skills. Questions often present a spill, a sterilization failure or a microscopy task and ask for the correct sequence.
Core rules and concepts
- Aseptic technique: work near a flame or in a laminar flow hood, flame loops, keep lids close, never mouth-pipette, label plates with name, date and organism.
- PPE includes lab coat, gloves and goggles. Biosafety levels range from BSL-1 (low risk) to BSL-4 (dangerous pathogens). Sharps go into puncture-resistant containers; cultures are autoclaved before disposal.
- Autoclave validation uses biological indicators (Geobacillus stearothermophilus spores), chemical indicators and physical monitoring. Media are sterilized at 121°C for 15 minutes unless heat-labile.
- Microscope care: carry with both hands, clean lenses with lens paper, start on low power, use oil immersion only with oil and wipe off afterwards. Record results and report spills.
Worked example
A culture of Escherichia coli is spilled on the bench. Reasoning: alert others, put on gloves, cover the spill with absorbent paper and apply freshly prepared disinfectant from the outside inward. After the contact time, wipe up with tongs or paper, place waste in a biohazard bag, and autoclave. Do not use a dry broom, which aerosolizes bacteria, and do not pour disinfectant down the drain before contact time.
Mark-losing traps
- Mouth pipetting is never acceptable, even with non-pathogenic cultures.
- An autoclave tape strip changing colour is not proof of sterilization; it is only a process indicator.
- Do not use oil immersion with the 10× objective or leave oil on the lens.
- Never discard cultures in ordinary bins or sinks without decontamination.