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Explain the importance of sterilsation,
Describe the role of moist heat in sterilization,
Recognize the basic requirements for steam sterilization,
Requirements for Sterilization.
1.1 Place a circular label on the cap of each of the five screw-capped bottles. Label the bottles 1
to 5.
1.2 Aseptically place a strip of paper impregnated with spores of B. stearothermophilus in
bottles 1 to 4.
1.3 Using the Pasteur pipette add several drops (5-6) of sterile water to bottle 2. Cover the spore
strip in bottle 4 with paraffin oil (make sure the spore strip is completely immersed in oil).
1.4 Ensure that the caps on bottles 2, 3 and 4 are screwed on tightly, and then place these three
bottles in the sterilizer.
Note: Bottle 1 is NOT to be processed.
1.5 Place the two ‘Thermalog’ strips in the two Schott bottles.
1.6 Add 2 ml of water into one bottle and loosely cap it.
1.7 Tightly cap the other bottle.
1.8. Place the two Schott bottles and a Sterikon plus Bioindicator vials in the sterilizer with the
other bottles and maintain at 121C for 15 min.
1.9 Do not sterilize the second Bioindicator vial.
BMS2052 Practical Manual 2017
1.10 On completion of the sterilizing cycle immediately examine the ‘Thermalog’ strips.
1.11 Add 3 ml of TSB directly to bottles 1, 2 and 3 and also bottle 5.
1.12 Aseptically transfer the spore strip from bottle 4 to bottle 5.
Note: Discard bottle 4 into the special paraffin discard.
1.13 Incubate the bottles and both Sterikon plus Bioindicator vials at 56oC for 3 days.
Results of the “Thermolog” Strips
1.14 Record any change in the colour of the ‘Thermalog’ strips. A blue colour will appear in the
transparent window into the ‘SAFE’ zone if the conditions required for sterilization were
2.1 Using visible turbidity as an index of growth, record the presence or absence of bacterial
growth in bottles 1, 2, 3 and 5.
2.2 Observe the Sterikon indicator vials for growth and colour change.
Discussion Questions
1. What properties of steam make it an ‘ideal’ sterilant?
2. Compare the biocidal action of moist and dry heat.
3. List the various stages that make up the sterilization time.
4. Explain the term tyndallisation.
5. Explain the reasons for culturing an unexposed spore strip when processing biological
6. Apart from heat, discuss other physical control methods available.
7. Can prions be destroyed by normal steam sterilisation process? Explain your answer.

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