Q1 Why is it necessary to heat-fix a smear?
Q2 Why is the hanging drop method used for observing motility?
Q3 Why should the volume never be set outside the specified range of a pipette?
Q4 Why should the push button of a pipette never be allowed to snap back?
Q5 When is it necessary to change tips when setting up serial dilutions?
Q6 Why should the liquid that remains in the tip in reverse technique never be included in the delivery?
Q7 List a further example of how the accuracy of preparing dilutions can be improved.
Eg. The larger the volume, the smaller the sampling error.
Q8 What is aseptic technique?
Q9 Describe one example of aseptic technique.
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Q10 List the key differences between pour plate and lawn culture.
Q11 Give an example of when an agar layer culture is used.
Q12 Using a diagram show how an organism can be inoculated onto a whole agar plate, a half-agar plate and a quarter agar plate to achieve single colonies. Indicate on the diagram at what stages a loop should be flamed.
○○○
Q13 Why is it important to obtain single colonies?
Q14 Why is it important to be able to count the number of viable bacteria?
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Q15 S. epidermidis in solution.
To determine the number of CFU of S. epidermidis in broth, 10-fold dilutions were prepared by adding 50 L of broth to 450 L of sterile MQ water to prepare the first dilution. Duplicate volumes of 10 L of each dilution and neat was inoculated onto nutrient agar using the drop technique. The following results were obtained:
Dilution
Replicate 1 (CFU)
Replicate 2 (CFU)
10-1
TNTC
TNTC
10-2
TNTC
TNTC
10-3
TNTC
TNTC
10-4
TNTC
TNTC
10-5
35
43
10-6
4
5
10-7
0
0
10-8
0
0
10-9
0
0
10-10
0
0
Calculate the number of CFU/ mL of S. epidermidis in the original broth solution.
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Q16 Calculate how to prepare 10 ml of 70% ethanol from absolute ethanol (96%).
Q17 Calculate how to prepare 10 mL of 96% ethanol.
Q18 Calculate how to prepare 1L of 1x TAE buffer from a 50x stock of TAE.
Q19 Calculate how to prepare 100 mL of a 1% agarose gel in 1x TAE buffer.
Q20 Calculate how to prepare 100 mL of 0.5 M NaCl. The MW of NaCl is 58.44.
Q21 Calculate how to prepare a 50 mL solution containing 40 mM TrisCl /1 mM EDTA / 0.15 M NaCl from stock solutions of 0.5 M NaCl, 0.5 M EDTA, pH 8.0 and 1 M TrisCl
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