Results of the Experiments
Name: Noor Alkemade
On this sheet you have to fill in results of the experiments, show it to the assistant for discussion.
Answer the questions which you can find in the manual at the experiments and below.
Exp 1: day 1 en 2 cells/ml (Be sure that you understand the calculation)
day 1: Cells/ml (via OD540):
day 2: CFU/ml (plating method):
1. Did you get discrete colonies after streaking?
Yes, after streaking I got a couple of discrete colonies.
2. How would you improve on your method, if needed?
If I used a more diluted sample to place on the plate, I would get more single colonies.
Now I only have a couple of colonies in the last strikes on the plate.
3. What are the (qualitative) differences between the colonies of B. cereus and S.
marcescens ?
The size of the colonies, also the spreading of the colonies looks different.
4. Are the dilution series any good? Among the plates, is there a suitable plate with a
countable number (30−300) of colonies?
Yes, there are suitable plates with a countable number of colonies. So the dilution is
done correctly.
5. Lessons learned: Would you proceed differently a next time? If so, what changes
would you make to the procedure?
No, I think the method is preformed correctly.
6. The count plate provides a number of living bacteria per ml. The optical thickness is
also a measure of the number of bacteria per ml, since the more cells there are, the
hazier the suspension becomes, and the greater the OD540. However, the numbers
obtained from the above two methods differ significantly. Can you argue why this is
the case?
Because the difference in the method that was used. The bacteria where not treated the
same way.
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Name: Noor Alkemade
On this sheet you have to fill in results of the experiments, show it to the assistant for discussion.
Answer the questions which you can find in the manual at the experiments and below.
Exp 1: day 1 en 2 cells/ml (Be sure that you understand the calculation)
day 1: Cells/ml (via OD540):
day 2: CFU/ml (plating method):
1. Did you get discrete colonies after streaking?
Yes, after streaking I got a couple of discrete colonies.
2. How would you improve on your method, if needed?
If I used a more diluted sample to place on the plate, I would get more single colonies.
Now I only have a couple of colonies in the last strikes on the plate.
3. What are the (qualitative) differences between the colonies of B. cereus and S.
marcescens ?
The size of the colonies, also the spreading of the colonies looks different.
4. Are the dilution series any good? Among the plates, is there a suitable plate with a
countable number (30−300) of colonies?
Yes, there are suitable plates with a countable number of colonies. So the dilution is
done correctly.
5. Lessons learned: Would you proceed differently a next time? If so, what changes
would you make to the procedure?
No, I think the method is preformed correctly.
6. The count plate provides a number of living bacteria per ml. The optical thickness is
also a measure of the number of bacteria per ml, since the more cells there are, the
hazier the suspension becomes, and the greater the OD540. However, the numbers
obtained from the above two methods differ significantly. Can you argue why this is
the case?
Because the difference in the method that was used. The bacteria where not treated the
same way.
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