Basic microbiology techniques — A/L Biology

What must I remember about Basic microbiology techniques?

• Sterilization eliminates all forms of microbial life including bacterial endospores: Heat sterilization (autoclaving: moist heat at 121°C, 15 psi for 15-20 min; hot air oven: dry heat at 160-170°C for 2 hours).
• Radiation and filtration sterilization: UV radiation (surface decontamination), Gamma radiation (heat-sensitive disposables: plastic petri dishes, syringes), Membrane filtration (0.22 µm pore size for heat-labile liquids: antibiotics, vitamins).
• Culture media preparation: Nutrient agar (solidifying agent agar-agar melting at ~85°C and solidifying at ~40°C), selective media (inhibits specific groups), and differential media (distinguishes metabolic traits).
• Aseptic techniques: Flaming loops/test-tube necks, working within 20 cm of a Bunsen flame or inside a laminar airflow cabinet to prevent environmental contamination.
• Inoculation methods: Streak plate technique (produces isolated single colonies for pure culture isolation), pour plate method, and spread plate technique (for viable bacterial quantification).

Test yourself (1 minute)

1. Autoclave parameters

   121°C at 15 pounds per square inch (psi) gauge pressure for 15-20 minutes; moist heat coagulates and denatures essential microbial enzymes and destroys resistant endospores.

2. Flaming inoculating loop

   Heat the wire loop until red hot along its entire length; allow it to cool inside the sterile zone before touching bacterial cultures to avoid killing the inoculum.

3. Petri dish incubation orientation

   Always incubate agar plates inverted (upside-down, lid at bottom) to prevent condensation droplets from falling onto the agar surface and smearing colonies.

Practise Basic microbiology techniques questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 9

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Where does Basic microbiology techniques fit in the syllabus?

Year 1 · Term 3