Microbiology Cheat Sheet
Sterilisation: Match Method to Material
Sterilisation by material for NEET-PG: autoclave, hot air oven, membrane filtration, ethylene oxide, glutaraldehyde, Spaulding classes, and prion protocols.
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Sterilisation: Match Method to Material
Sterilisation by material for NEET-PG: autoclave, hot air oven, membrane filtration, ethylene oxide, glutaraldehyde, Spaulding classes, and prion protocols.
This topic covers the classification and applications of sterilisation and disinfection, matching the appropriate method to the material and clinical situation.
High-yield lines
- Sterilisation destroys all microbial life including endospores, while disinfection eliminates most pathogens except spores from inanimate objects.
- The Spaulding classification divides devices into critical (require sterilisation), semi-critical (high-level disinfection), and non-critical (low-level disinfection).
- Autoclaving at 121 degrees Celsius, 15 psi, for 15 to 20 minutes is the gold standard, killing all organisms including endospores.
- The biological indicator for autoclave efficacy is Geobacillus stearothermophilus spore strips.
- The hot air oven at 160 degrees for 60 minutes uses dry heat for glassware, powders, and oils, monitored with Bacillus atrophaeus.
- Air removal is critical for autoclave efficacy, and the Bowie-Dick test checks air removal in pre-vacuum autoclaves.
- Membrane filtration through a 0.22 micrometre pore sterilises heat-labile liquids such as serum, antibiotics, and vitamins by removing bacteria.
- Ethylene oxide gas sterilises heat-sensitive devices like plastics and electronics but requires a prolonged aeration period due to toxicity.
- Glutaraldehyde 2 percent provides high-level disinfection of endoscopes and heat-sensitive semi-critical instruments.
- Gamma irradiation at 25 kilograys sterilises single-use disposables such as syringes, sutures, and catheters at manufacture.
- Ultraviolet radiation at 254 nanometres causes thymine dimers and is used for surface and air disinfection, not sterilisation.
- The resistance hierarchy from most to least resistant is prions, spores, mycobacteria, cysts, non-enveloped viruses, fungi, vegetative bacteria, then enveloped viruses.
- CJD-contaminated instruments require 1N sodium hydroxide soak plus autoclaving at 134 degrees for 18 minutes, as routine sterilisation is insufficient.
- Alcohols at 70 percent and chlorhexidine are not sporicidal and are used for skin antisepsis and intermediate-level disinfection.
Mapped competency codes
- MI1.4
- MI1.5
Continue into the full chapter
This summary maps to MI1-general-microbiology-and-immunity.
Frequently Asked Questions
Which method sterilises heat-labile liquids such as serum and antibiotics?
Membrane filtration through a 0.22 micrometre pore, which physically removes bacteria without heat.
What is the biological indicator for autoclave sterilisation?
Geobacillus stearothermophilus spore strips, whose negative culture after exposure confirms sterilisation.
How are CJD prion-contaminated instruments decontaminated?
By 1N sodium hydroxide soak for 1 hour plus autoclaving at 134 degrees Celsius for 18 minutes, since routine sterilisation is inadequate.
Which method is appropriate for a heat-sensitive flexible endoscope?
High-level disinfection with 2 percent glutaraldehyde or peracetic acid, as it is a heat-sensitive semi-critical device.
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