required pratical 6

Question 1

state 6 aspectic techniques

Answer 1

1. wipe down surfaces with antibacterial cleaner before and after experiment
2. use a bunsen burner so that convection currents draw microbes away from culture
3. flame the wire hoop before using it to transfer bacteria
4. flame the neck of any bottles before using to prevent bacteria entering the vessel
5. keep all vessels containing bacteria open for the miniumum about of time
6. close windows and doors to limit air currents

Question 2

method

Answer 2

1. carry out 6 aspectic techniques
2. use sterile pipette or wire hoop to transfer bacteria from broth to agar plate
3. spread bacteria evenly over plate using sterile plastic spreader
4. use sterile forceps to place multi disc antibotic ring on the plate, ring should only be moved by centre
5. lightly tape on lid and incubate at 25c for 48 hours
6. sterilise equipment
7. measure diameter of inhibition zone and work out area

Question 3

why is bacteria incubated at 25c?

Answer 3

to prevent growth of pathogens which occurs at higher temperatures

Question 4

why don’t you tape around entire lid?

Answer 4

prevents oxygen entering and so promotes the growth of harmful anaerobic bacteria

Question 5

how can you comapre the effectiveness of different antibiotics applied to the same bacteria?

Answer 5

calculate the zone of inhibition (clear area) on agar

Question 6

what does the zone of inhibition indicate?

Answer 6

it indicates the bacteria killed by the antibiotic, the larger the zone, the more effective the antibiotic