required practical 6

Question 1

what is the aim of this practical?

Answer 1

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

Question 2

what are key aseptic techniques to follow in this practical?

Answer 2

disinfect surfaces before and after the experiment with antimicrobial cleaner
have a lit Bunsen burner in your workspace so the convection currents continually sterilise the air
flame the inoculating hoop before using it to transfer bacteria
flame the neck of the bacteria culture bottles
open any vessels containing bacteria for the minimum amount of time

Question 3

what is a risk assessment for this practical?

Answer 3

hazard/risk/prevention
disinfectant/flammable/keep away from naked bunsen burner flame
bunsen burner/burns or scalds/keep flammable materials away from flame, tie back long hair, wear goggles
bacteria culture/contamination or infection/follow aseptic technique

Question 4

what is the method for this practical using streaking?

Answer 4

1. sterilise surfaces using antibacterial disinfectant before practical
2. light bunsen burner so convection currents help sterilise the air
3. place inoculating loop in bunsen burner to sterilise
4. open bacteria broth and flame neck of bottle
5. use sterilised inoculating loop to transfer bacteria from broth to agar plate and streak bacteria against agar
6. sterilise inoculating loop again before placing on surfaces
7. use sterile forceps to hold centre of antibiotic multodisc and place onto agar plate
8. partially tape lid of Petri dish on
9. incubate bacteria sample at 25 degrees

Question 5

what is the alternative method for this practical?

Answer 5

instead of using an inoculating loop to transfer the bacteria to the agar, use a sterile plastic pipette
then use a sterilised plastic spreader to distribute an even layer across the surface

Question 6

why shouldn’t the Petri dish be taped all the way around?

Answer 6

this will stop oxygen from getting in which could cause harmful anaerobic bacteria to grow

Question 7

why shouldn’t the bacteria be incubated above 25 degrees?

Answer 7

if they are incubated at human body temperature, this could cause pathogens which are harmful to humans to grow

Question 8

how should you analyse the results of the practical?

Answer 8

measure the diameter of the zone of inhibition for each antibiotic, then calculate the area (pi x d^2/4)