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What is the primary purpose of sterilization?
What is the primary purpose of sterilization?
Which of the following methods is classified as a mechanical sterilization method?
Which of the following methods is classified as a mechanical sterilization method?
What is one characteristic of microbicidal agents?
What is one characteristic of microbicidal agents?
Why is moist heat considered more effective for sterilization than dry heat?
Why is moist heat considered more effective for sterilization than dry heat?
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Which process can be considered as a form of controlled microbial growth but not true sterilization?
Which process can be considered as a form of controlled microbial growth but not true sterilization?
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What distinguishes microbiostatic agents from microbicidal agents?
What distinguishes microbiostatic agents from microbicidal agents?
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Which of the following statements about boiling as a sterilization method is true?
Which of the following statements about boiling as a sterilization method is true?
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In terms of sterilization methods, which statement is correct regarding radiation?
In terms of sterilization methods, which statement is correct regarding radiation?
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What is the minimum temperature and pressure required for effective autoclaving?
What is the minimum temperature and pressure required for effective autoclaving?
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Which of the following materials is NOT suitable for dry heat sterilization?
Which of the following materials is NOT suitable for dry heat sterilization?
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What mechanism does dry heat use to destroy microorganisms?
What mechanism does dry heat use to destroy microorganisms?
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What is the significance of the condensed liquid in steam sterilization?
What is the significance of the condensed liquid in steam sterilization?
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At what temperature and duration should glassware be sterilized using a hot air oven?
At what temperature and duration should glassware be sterilized using a hot air oven?
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Which of the following statements about autoclaves is true?
Which of the following statements about autoclaves is true?
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Why is dry heat sterilization appropriate for oily materials?
Why is dry heat sterilization appropriate for oily materials?
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What is the effect of increasing pressure on the boiling point of water during sterilization?
What is the effect of increasing pressure on the boiling point of water during sterilization?
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What is a primary application of membrane filtration?
What is a primary application of membrane filtration?
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Which method is generally considered most suitable for filtration under pressure?
Which method is generally considered most suitable for filtration under pressure?
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What category does sterile/membrane filtration fall under regarding sterilization methods?
What category does sterile/membrane filtration fall under regarding sterilization methods?
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Which of the following is NOT one of the four main types of sterilization discussed?
Which of the following is NOT one of the four main types of sterilization discussed?
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What is the state of the filtrate immediately after membrane filtration?
What is the state of the filtrate immediately after membrane filtration?
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What is the primary purpose of chemical sterilization?
What is the primary purpose of chemical sterilization?
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Which of the following methods is classified under dry heat sterilization?
Which of the following methods is classified under dry heat sterilization?
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What is a key advantage of gaseous sterilization compared to liquid sterilization?
What is a key advantage of gaseous sterilization compared to liquid sterilization?
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Which condition indicates that liquid sterilization is the appropriate choice?
Which condition indicates that liquid sterilization is the appropriate choice?
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What is a common issue associated with gaseous sterilization?
What is a common issue associated with gaseous sterilization?
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What is an example of non-ionising radiation mentioned?
What is an example of non-ionising radiation mentioned?
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Which of the following processes is considered an example of moist heat sterilization?
Which of the following processes is considered an example of moist heat sterilization?
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What differentiates gaseous sterilization from liquid sterilization?
What differentiates gaseous sterilization from liquid sterilization?
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What is the primary function of sodium hypochlorite?
What is the primary function of sodium hypochlorite?
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How long must devices be submerged in sodium hypochlorite to achieve sterilization?
How long must devices be submerged in sodium hypochlorite to achieve sterilization?
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What effect does sodium hypochlorite have on metallic equipment?
What effect does sodium hypochlorite have on metallic equipment?
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What is the main characteristic of membrane filtration?
What is the main characteristic of membrane filtration?
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What size particles can filter membranes in membrane filtration prevent from passing through?
What size particles can filter membranes in membrane filtration prevent from passing through?
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In addition to sterilization, what other purpose can membrane filtration serve?
In addition to sterilization, what other purpose can membrane filtration serve?
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What does the process of membrane filtration involve?
What does the process of membrane filtration involve?
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Which of the following is a property of sodium hypochlorite as an oxidizing agent?
Which of the following is a property of sodium hypochlorite as an oxidizing agent?
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What is a major advantage of moist heat sterilization compared to dry heat sterilization?
What is a major advantage of moist heat sterilization compared to dry heat sterilization?
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Which type of radiation is effective against both vegetative cells and endospores?
Which type of radiation is effective against both vegetative cells and endospores?
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What is a disadvantage of using non-ionising radiation like UV light?
What is a disadvantage of using non-ionising radiation like UV light?
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In the context of sterilization, which materials are most suitable for dry heat sterilization?
In the context of sterilization, which materials are most suitable for dry heat sterilization?
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What effect does UV radiation have on DNA?
What effect does UV radiation have on DNA?
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What temperature and duration are typically used in infrared sterilization?
What temperature and duration are typically used in infrared sterilization?
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Which of the following describes a limitation of ionising radiation?
Which of the following describes a limitation of ionising radiation?
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Which sterilization method may cause thermal shock to glassware?
Which sterilization method may cause thermal shock to glassware?
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Study Notes
Basic Microbiology Techniques - Sterilization
- Sterilization is a method of microbial control that aims to eliminate all forms of microbial life, including vegetative cells, endospores, and viruses.
- Sterilization is not the same as disinfection or anti-microbial or microbiostats or microbicidal agents,
- The four main sterilization types focus on heat, radiation, chemical and sterile/membrane filtration.
- Heat sterilization is the most effective and widely used method. It works through the destruction of enzymes and other essential cell constituents, operating more efficiently in a fully hydrated state.
Modes of Microbial Control
- Microbicidal: Kills microbes and/or reduces the cell number.
- Microbiostatic: Stops or inhibits microbial growth, maintaining a constant viable cell count.
Classification of Sterilization Methods
- Physical: Heat and Radiation
- Chemical: Liquid and Gaseous Sterilants
- Mechanical: Filtration
Heat Sterilization - Physical Method
- Most effective and widely used method.
- Heat sterilisation is microbicidal, destroying enzymes and other cellular components.
- Efficiency is enhanced in a fully-hydrated state, needing lower temperatures and shorter durations.
Different Modes of Heat Sterilization
- Moist Heat: Steam under pressure.
- Dry Heat: Red Heat, hot air (oven), ethanol flaming.
Moist Heat Control
- Boiling: Not sterilization, kills vegetative cells of pathogens at 100°C for at least 20 min, but does not destroy all endospores.
- Pasteurization: Not sterilization, heats food to kill vegetative cells (135°C for 15 seconds or 63°C for 30 minutes).
- Steam Under Pressure (Autoclaving): Sterilisation, kills all viable microorganisms (including endospores) at 121°C under 15 psi for 15 min.
Steam Under Pressure/Steam Sterilization/Autoclaving
- Water boils at 100°C under normal atmospheric pressure (760 mm Hg).
- Boiling point increases with increased pressure.
- Autoclave: pressure at 15 PSI (775 mm Hg) for water to boil at 121°C; higher penetrating power kills all microbes including endospores and some viruses.
- Condensed steam ensures moist killing.
Dry Heat Sterilization
- Destroys microorganisms by denaturing and lysing proteins.
- Appropriate for moisture-sensitive substances (and materials practically impossible to sterilize with moist-heat).
- Examples include powders, oily materials, and laboratory equipment like Petri dishes and pipettes.
Hot Air Oven - Dry Heat Sterilization
- Temperature and duration requirements vary (e.g., 170°C for 30 min, 160°C for 60 min, 150°C for 150 min).
- Suitable for sterilizing glassware, Petri dishes, and powder samples.
Red Heat/Ethanol Flaming - Dry Heat Sterilization
- Methods covered in streak and spread plate topics
Comparison of Moist vs Dry Heat
- Moist Heat: More effective, uses lower temperatures and shorter durations; can corrode some materials like metal. Suitable for materials like rubber, plastic, textiles, etc and materials through which steam penetrates easily.
- Dry Heat: Requires higher temperatures and longer durations; doesn't corrode metals; may cause thermal shock to glassware; good for powders, oils, etc; not suitable for heat-sensitive materials.
Radiation - Physical Method
- Non-ionizing: Infrared, Ultraviolet
- Ionizing: X-rays, gamma rays, high-speed electrons, cosmos rays.
- UV light (around 260 nm) leads to abnormal DNA bond formation, used for biological safety cabinets.
- Ionizing radiation effective against vegetative cells and endospores.
- Radiation is used for food, medicine, and heat-sensitive products (plastics), but does not always affect viruses. It damages DNA, causes chemical changes in cell organelles, and produces toxic substances.
Infrared (IR) Radiation
- Absorbed and converted to heat energy.
- Used in a tunnel that is used to sterilize instruments and glassware, which are placed in a tray on a conveyor belt moved through the tunnel.
Chemical Sterilization: Gaseous or Liquid
- Gaseous Sterilization: Ethylene oxide, formaldehyde, nitrogen dioxide (NO2), ozone.
- Liquid Sterilization: Hydrogen peroxide, glutaraldehyde, hypochlorite.
- Used for heat-sensitive materials like plastics, and/or biological specimens.
Hypochlorite
- Sodium hypochlorite (bleach) is a disinfecting agent.
- Submerging in hypochlorite for 20-24 hours is needed to reach sterilization level.
- Acts by oxidizing organic compounds; corrosive to metal.
- Can be used at appropriate concentrations to disinfect surfaces and clean blood spills.
Sterile/Membrane Filtration - Mechanical Method
- Removes rather than destroys microorganisms.
- Used for heat-sensitive culture media in a vacuum filter tower.
- Filters have tiny pores to allow liquid to pass but prevent larger particles, thus is good for clearing fluids and sometimes gases.
Membrane Filtration - Sterilization of Liquids
- Assembled pressure-operated filter holders are used for syringe mounting and in-line use.
- Vacuum filtration tower devices are used for filtration.
- Filtration under pressure is suitable.
- Filtrate becomes sterile after filtration.
Summary of Physical Antimicrobial Methods
- Moist Heat: Boiling, Pasteurization, Steam under pressure
- Dry Heat: Red heat, Ovens, Ethanol Flaming
- Radiation: Ionising, Non-ionising
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Description
This quiz covers fundamental microbiology techniques focusing on sterilization methods. Learn about the different types of sterilization—heat, radiation, chemical, and filtration—and their applications in microbial control. Understand the differences between microbicidal and microbiostatic methods.
