Paper I — 2013 September (Supplementary) (2010 Scheme) — Q3
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Paper I
2013 September (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Moist heat sterilization techniques.
Q35 marksShort Essays
Answer
Moist heat kills microorganisms by denaturing and coagulating proteins — more efficient than dry heat because water molecules facilitate protein denaturation at lower temperatures and shorter exposure times.
Techniques
Below 100°C:
Pasteurization — holder method (63°C/30 min) or flash/HTST method (72°C/15–20 sec); kills pathogens in milk without destroying nutritive quality; not sterilization.
Vaccine bath — 60°C for 1 hour, used in preparing killed bacterial vaccines.
At 100°C:
Boiling (100°C, 10–30 min) — kills vegetative organisms, not all spores.
Tyndallisation (intermittent sterilization) — steaming at 100°C for 20 minutes on three successive days with intervening incubation, allowing spores to germinate between cycles and then be killed; used for heat-labile fluids/media.
Steaming (Koch’s/Arnold’s steamer) — free-flowing steam at 100°C, similar application to Tyndallisation.
Above 100°C (under pressure):
Autoclaving — the standard and most reliable method; steam under pressure (15 lbs/sq inch, 121°C, 15–20 minutes) kills even resistant bacterial spores; used for surgical instruments, culture media, dressings, and rubber goods.
Sterilization control: monitored using chemical indicators (autoclave tape, Bowie-Dick test) and biological indicators (Geobacillus stearothermophilus spore strips) to confirm sterilizing conditions were actually achieved.
