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required practical - Coggle Diagram
required practical
Method
- Make sure hands are clean and switch bunsen flame to blue.
- With a pen divide the bottom of the petri dish into 3 different sections and label them 1,2,3 around the edge. Also place a dot in the middle of the petri dish and around the edge write your initials, the date and the name of the bacteria.
- Then remove the lid of the bottle containing the bacteria, then quickly flame the neck of the bottle through the bunsen flame. Continue to collect 1ml of the bacteria in a pipette.
- Put the bunsen burner on a heatproof mat. Light the bunsen on a yellow flame.
- Quickly flame the neck of the bottle through the bunsen burner again and replace the lid.
- Sterilise the benchkote where you are working with ethanol and cotton wool.
- Continue by lifting the lid of the petri dish at an angle and pipette the bacteria onto the petri dish and replace the lid again. Turn the bunsen flame back to yellow.
- Collect a bottle of agar from the water bath and quickly lift the lid at an angle and pour the agar into the dish. Carefully move the dish in a N E S W movement to spread the agar evenly.
- After leaving it for 5 minutes put different antiseptics into 3 filter paper discs. Then use sterilised forceps to carefully put each disc onto one of teh dots on the bottom of the petri dish.
- Label where each antiseptic is in the different sections on the bottom of the plate.
- Finally secure the lid of the agar plate in place using clear tape. Then incubate the plate at 25°C for 48 hours.
Aseptic technique
• To minimise exposure of agar to air quickly lift lid away from your face and pipette bacteria into the petri dish and replace lid.
• Inoculating loops are used to transfer microorganisms to the media. MUST be sterilised by passing them through a flame.
• Lid of petri dish must be sealed with adhesive tape, this prevents microorganisms from the air contaminating the culture.
• Petri dishes and bench must be STERILISED before use to kill unwanted microorganisms using ethanol or disinfectant.
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Variables
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Control variable
Size of petri dish, amount of agar, same amount of antiseptics, same amount of bacteria at beginning, the same type of bacteria throughout.
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Zones of inhibition
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After growth
After 24 hours there are no bacterial growth (zones of inhibition) around a few of these antibiotics while the rest of the petri dish is covered with bacterial growth.