Unit 6: investigative project: the effect of penicillin on bacterial growth.
P4/P6:
Introduction:
This report will present how the antibiotic penicillin will have an effect on bacterial growth.
Antibiotics are known to be useful medications to kill or slow down the rate of bacterial
reproduction. Bacteria can be replicated during binary fission as it is a form of cell division.
Bacteria are known to grow on nutrient broth solution which allows bacteria to multiply
because the solution provides sufficient nutrients for it to grow, as well as on agar plates
where the hot molten agar is put into sterilized Petri dishes. The bacterium is then formed
into individual colonies. During the experiment, results will show that some bacteria can
have a contaminating effect meaning that penicillin will react and create an inhibition zone
where it killed the bacteria.
Because I’ve encountered an issue with my method of using a concentration of penicillin
with different concentrations of bacterial solution, after the first 24 and 48 hours the
penicillin did not seem to have an effect of killing the bacteria around it, so I have changed
my plan and I replaced the penicillin to antiseptic to obtain results.
Preliminary results:
1st petri dish 2nd petri dish 3rd petri dish
Penicillin Radius: 3 mm Radius: 5mm Radius: 2mm
Diameter: 6mm Diameter: 10mm Diameter: 4mm
Old method used:
Hypothesis: A lower concentration of bacterial solution will allow a fixed concentration of
penicillin to kill the bacteria more quickly.
Method 1:
Investigating the effect of a fixed concentration of penicillin on different concentrations of
bacteria solution to see how bacteria grows.
1. Prepare equipment to be sterilized using the aseptic technique:
2. Set up 5 different agar plates. Label each petri dish with how much concentration
needs to be used, the date and name.
3. Light up a Bunsen burner, set it to an orange flame and place the agar plates near
the Bunsen burner, this ensures that no contamination will take place. The agar
plates must be closed.
4. Switch the flame of the Bunsen burner to a safety blue flame and heat the neck of
the bottle of the E. coli bacterial solution. Switch again the orange flame of the
Bunsen burner.
5. Then using a sterile micro pipette, measure different concentrations of bacterial
solution when adding in each petri dish. Open the lid of the Petri dish near the
Bunsen orange flame placing the different concentrations of bacteria solution.
, Increase concentration of bacteria by 10 micro ml each time. For example, use 10
micro ml, 20 micro ml,30 micro ml, 40 micro ml and 50 micro ml.
6. A wire hoop should be heated in the Bunsen blue flame to remove any
contamination. Open each petri dish at a time making streaks on the agar plate.
7. The Bunsen blue flame should be used again to heat the forces to pick up the paper
disc soaked in antibiotic. Again, open the lid of each petri dish and insert the disc
carefully.
8. Close the lid of each petri dish and seal them around using Sellotape, do not tape
them all the way around. Place the plates in an oven at 25°C and allow the bacteria
to grow over the next 24 hours.
9. After 24 hours, do not open the petri dish, measure the diameter of the inhibition
zone around the penicillin in each petri dish using a ruler.
The method tested:
Hypothesis: a greater concentration of antibiotic; penicillin will kill the bacteria growing in
the petri dish in a larger area.
Null hypothesis: a greater concentration of antibiotic; penicillin will have no significant
effect at killing the bacteria growth in the petri dish in a larger area.
Investigating the effect of different concentrations of antiseptic (penicillin) to see if it affects
bacterial growth.
1. Prepare equipment to be sterilized using the aseptic technique:
the workspace and Petri dish must be sterilized using antibacterial cleaner before
and after the experiment.
Using the Bunsen burner flame to heat the neck of the bacteria bottle.
The windows and doors need to be closed to limit the air currents.
The Bunsen flame should be at safety flame so that it creates a sterile environment.
2. Set up 5 different agar plates. Label each petri dish with how much concentration of
disinfectant needs to be used, the date and name.
3. Light up a Bunsen burner, set it to an orange flame and place the agar plates near
the Bunsen burner, this ensures that no contamination will take place. The agar
plates must be closed. MAKE SURE THAT ANY BOTTLES OF ANTIBACTERIAL
SOLUTION OR FLAMMABLE SUBSTANCES ARE CLOSED BEFORE TURNING ON THE
BUNSEN BURNER.
4. Switch the flame of the Bunsen burner to a safety blue flame and heat the neck of
the bottle of the E. coli bacterial solution. Switch again the orange flame of the
Bunsen burner.
5. Then using a sterile micro pipette, measure the concentration of bacterial solution
when adding in each petri dish. Open the lid of the Petri dish near the Bunsen orange
flame placing the concentrations of bacteria solution.
6. A sterilised glass rod should be used to spread the bacteria on the petri dish. Open
each petri dish at a time to spread the bacteria then close the lid to prevent
contamination.
, 7. Using a micropipette measure different concentrations of disinfectant and place in
each agar plate. The concentrations will increase by 1 ml each time. So 1ml,2 ml,
3ml,4 ml, 5 ml.
8. Close the lid of each petri dish and seal them around using Sellotape, do not tape
them all the way around. Place the plates in an oven at 25°C and allow the bacteria
to grow over the next 24 hours.
9. After 24 hours, do not open the petri dish, measure the diameter of the inhibition
zone around the penicillin in each petri dish using a ruler.
Self-citation:
Oana H. (2022), method of testing
different concentrations of
antiseptic on bacterial growth.
P7: Practical skills during the experiment:
- Organisation: When I have put my method into practice, I used a tray where I’ve put
all the equipment needed so that I prevented equipment made from glass from
rolling on the working area and fall. My organisation skills was developed throughout
as I was making sure that the equipment in the tray was placed in the order that I
needed it and I ticked off the equipment from the equipment list. I also placed each
equipment back in the tray at the very same spot that was originally arranged after
using it.
- Handling the equipment carefully: when using the micropipette, we needed to use
different disposable micropipette tip at each trial to make sure that contamination
doesn’t occur and therefore all equipment is safe to use. By changing the tip for each
petri dish continuously, developed my skill in handling the equipment in an
investigation carefully without dropping it.
- Handling toxic chemicals such as ethanol: ethanol is an alcohol which can present
some hazards in the experiment because it is very flammable. In the aseptic
technique, we used ethanol soaked in a cotton pad and forceps to wipe the surface
area because with hands would have been dangerous, so we had to wait a couple of
minutes for it to dry off before lighting the Bunsen burner. Also, we used the ethanol
in sterilising the glass spreader after using it after each petri dish and burned it in the
Bunsen flame to dry it.
- Transferring biological material such as bacteria: the experiment should be done in
a safe working area to prevent contamination of culture which is included in the
aseptic technique where for example the inoculating rod had to be sterilised in the
ethanol then burned in the Bunsen flame, so it dries off.
