practical aspect

Question 1

Why are aseptic techniques used when culturing microorganisms?

Answer 1

To prevent contamination of cultures by unwanted microorganisms.

• contaminated cultures may slow down growth rate, give imprecise results or even be hazardous to health
• contamination on industrial scale is costly because entire cultures may have to be thrown away

Question 2

Important aseptic techniques examples:

Answer 2

• disinfect work surfaces
• work near a bunsen burner flame, this is because as hot air rises any microorganisms in the air are drawn away from the culture
• sterilise instrument used to transfer cultures before and after each use.( e.g. wire inoculation loop), by passing it through a bunsen burner flame for 5 secs
• minimise time agar plate is left open and put lid on as quickly as possible
• sterilise all glassware before and after use in an autoclave ( machine that steams equipment at high pressure)
• wear lab coat and gloves

Question 3

Measuring the effects of temperature on the growth of bacteria:

Answer 3

1) Using a sterile pipette add a set volume (e.g. 0.1cm3) of sample to an agar plate, discard pipette safely
2) Spread broth across the entire surface of the agar, using a sterile plastic spreader, discard spreader safely after use.
3) put lid on agar plate and lightly tape it shut with 2 pieces of tape
4) repeat steps 1-3 until you have 6 plates
5) place 3 of the plates in a fridge at 4 degrees Celsius, and place the other 3 plates in an incubator at 25 degrees Celsius.
6) put a 1 lidded agar plate in the fridge at 4 degrees and 1 agar plate in the 25 degrees incubator. Plates should be uncultured ( no bacteria added to them).
- these plates act as negative controls
7) leave all plates for same amount of time (48 hours)
8) If bacterial growth has occurred, you should see colonies of bacteria on surface of the agar.
9) Count the number of colonies that have been formed on each plate and record results in a table
10) work out mean number of colonies formed at each temperature

Question 4

Why most agar plates be incubated upsidedown

Answer 4

This is to prevent any condensation that forms on the lid from dropping onto agar.