RP6: The use of a septic techniques to investigate the effects of antibiotics on microbial growth

Question 1

What is an aseptic technique

Answer 1

It is working in sterile conditions to prevent bacteria from spreading/contaminating the experiment

Question 2

What are two examples of aseptic techniques

Answer 2

biocide solution

Flaming

Question 3

What are we looking at in this experiment

Answer 3

we will use four different concentrations of penicillin to see the affect that these have on the growth of bacterium

Question 4

What is the procedure for this practical

Answer 4

1: keep the lid on whilst you label the base of the petri dish with your initials and your selected penicillin concentration
2: gently shake the bottle of bacterial broth and carefully remove the lid. Past the neck of the bottle quickly through the hot flame of the Bunsen burner.
3: use a sterile pipette to transfer two drops of the bacteria broth onto the centre of a petri dish quickly replacing the lid of the petri dish.
4: reflame the neck of the bottle of bacteria broth and replace the lid.
5: Place a sterile plastic spreader onto the centre of the surface and quickly rotate the dish evenly to disperse the bacterial growth across the whole of the petri dish. Replace the lid of a petri dish.
6: pass the end of the forceps through the flame of a Bunsen
7: Remove the lid of the McCartney bottle flame the neck using the called flame forceps and remove one sterile filter disk.
8: reflame the neck of the McCartney bottle quickly and replace the lid.
9: Remove the lid of the penicillin pass the neck through the Bunsen flame and get the paper desk into the penicillin solution for 10 seconds shake to remove excess solution
10: re-flame the neck of the bottle containing the disks and replace the lid
11: placed the soaked disc Kathleen into the centre of the petri dish, replace the lid
12: The dishes will be incubated for 25°C for two days

Question 5

what do you do with the results

Answer 5

Find the mean diameter of each penicillin concentration and find the mean surface area called the zone of inhibition for each penicillin concentration again

Question 6

Work out the standard deviation for each penicillin concentration. What does it mean if a standard deviation bars overlap

Answer 6

that the results imply no statistically significant difference between the enzyme activity of the control and treated groups

Question 7

What does a low standard deviation indicates

Answer 7

That the data points tend to be very close to the mean so that the data may be more reliable

Question 8

What does a larger/higher standard deviation suggest

Answer 8

That the data points or more spread out over a large range of values so the data may be less reliable

Question 9

How do you plot a graph for this information

Answer 9

Y axis: Mean Area for the zone of inhibition millimetres squared
X axis: Concentration of penicillin percentage

Question 10

Give one way in which antibiotics can prevent the growth of bacteria

Answer 10

antibiotics can prevent the bacteria from synthesising Murin/peptidoglycan in the cell walls. Therefore bacteria cannot replicate

Question 11

When taking samples of bacteria doctors use samples of bacteria taken from many patients in the hospital. Explain why this was important

Answer 11

Taking multiple samples from different patients gives a more representative sample. Different patients could have different types/versions of this bacteria and it allows the doctors to compare the range of samples.

Question 12

Why would you place the Bunsen burner close to the edge of the heat proof mat

Answer 12

This enables you to work close to the Bunsen burner. So that any air that is exposed when you slightly open the lid on the plate is going to be sterilised by the heat from the Bunsen burner.

Question 13

Give an example of an aseptic technique (washing)

Answer 13

wash your hands with soap thoroughly and dry with a paper towel

Question 14

Why would you try to open the lid as little as possible

Answer 14

This prevents microbes in the air landing on your plate

Question 15

Give the main two reasons why aseptic techniques are used (explanation)

Answer 15

to kill any other bacteria, and to prevent contamination on your plate

To make sure you are maintaining a pure culture of the specific bacteria you are growing

Question 16

Why is it important you don’t have contaminations on your plate

Answer 16

If a pathogenic strain grows this could be harmful. You don’t want other bacteria to outcompete the bacteria you are growing. (You don’t want them competing for resources for example oxygen and nutrients in the agar). They could outcompete your bacteria and prevent your bacteria from growing.

Question 17

What is the zone of inhibition

Answer 17

it is the area around the Paper disk where the bacteria has been killed.

Question 18

How would you set up a control for this experiment

Answer 18

you would soak the Paper disk in water not in antibiotic. to prove that it is not the paper disc itself that is killing the bacteria.

Question 19

Why are the plates incubated at 25°C when the optimum is 30 to 35°C

Answer 19

To prevent the excessive growth of bacteria and pathogens from growing

Question 20

Why do you not Sellotape around the whole rim of the plate

Answer 20

This allows oxygen to still enter into the plate. So that anaerobic bacteria don’t grow. As anaerobic bacteria are often pathogenic