required practical 6

Question 1

what is practical 6

Answer 1

use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Question 2

aim of 6

Answer 2

Aseptic techniques​​ are used to ​avoid contamination​​ of the sample from outside substances such as microorganisms. This is important to get​ reliable ​​and ​repeatable data.

Question 3

6 - aseptic techniques

Answer 3

● Wipe down surfaces with ​antibacterial cleaner,​​ both ​before and after experiment.
● Use a ​Bunsen burner​​ in the work space so that ​convection currents​​ draw microbes away from the culture.
● Flame the wire hoop​​ before using it to transfer bacteria.
● Flame the neck of any bottles​​ before using them to prevent any bacteria entering the vessel (air moves out so unwanted organisms don’t move in).
● Keep all vessels containing bacteria​ ​​open for the minimum amount of time.
● Close windows and doors​​ ​​to limit air currents.

Question 4

6 - equipment list

Answer 4

● Bacteria sample
● Disinfectant
● Bunsen burner
● Heatproof mat
● Ethanol
● Wire hoop
● Pipette
● Forceps
● Plastic spreader
● Prepared agar plate
● Multodisc antibiotic ring
● Ruler

Question 5

6 - method

Answer 5

1. Carry out ​aseptic techniques​​ detailed above.
2. Use a ​sterile pipette​​ ​​or ​wire hoop​​ to transfer bacteria from ​broth​​ ​(distilled
   water, bacterial culture, nutrients) to ​agar plate ​​(petri dish containing agar jelly).
3. Spread bacteria evenly​​ ​over plate using a ​sterile plastic spreader​​.
4. Use ​sterile forceps​​ to place a ​multi disc antibiotic ring​​ on the plate. Ring
   should only be moved by holding the centre, NOT the arms.
5. Lightly tape a lid on, ​invert​​ and ​incubate​​ at 25°C for 48 hours. DO NOT tape
   around the entire dish as this ​prevents oxygen entering​​ and so promotes the
   growth of more harmful ​anaerobic​​ bacteria.
6. Sterilise equipment​​ used to handle bacteria and​ disinfect work surfaces.

after incubation

7. Measure the ​diameter​​ of the ​inhibition zone​​ (clear circle) for each antibiotic. DO NOT remove the ​lid​​ from the agar plate.
8. Work out the ​area​​ of the inhibition zone using the formula:

Area = pi x diameter^2 / 4

NB: Bacteria sample is incubated at ​25°C​​. This is because incubating at ​37°C​​ (human body temperature) could enable pathogens to grow that are ​harmful to humans

Question 6

6 - risk assessment

Answer 6

disinfectant - flammable