ch 13 Sterilization

What is sterilization?

Elimination or inactivation of ALL microorganisms, including endospores.

What is disinfection?

Reduction in the number of microorganisms, especially pathogens. It does not necessarily eliminate all microbes.

What does bactericidal mean?

An agent that destroys bacteria.

What does bacteriostatic mean?

An agent that inhibits bacterial growth.

What is an antiseptic?

A disinfecting agent that is safe to use on living tissue

What is sanitization?

Cleaning that reduces the number of pathogens and microorganisms.

Why is heat effective at controlling microorganisms?

Heat denatures proteins and removes water, damaging or killing microorganisms

Does boiling reliably sterilize an object?

No. Boiling at approximately 180°F for 10 minutes may kill many microorganisms, but endospores can survive.

What is direct flame sterilization?

Using an open flame to destroy microorganisms. It is inexpensive and fast but cannot be used on flammable or meltable materials that need to be preserved.

What is a hot air oven used for?

Dry heat sterilization at 160°C for 2 hours. It is useful for materials that need to remain dry, such as glassware.

What is an autoclave?

A sterilization device that uses heat, pressure, steam, and vacuum to destroy microorganisms, including endospores.

What are the standard autoclave conditions?

121°C, 15 psi, for 15 minutes.

Why is an autoclave considered the most reliable sterilization method?

It uses pressurized steam and high temperatures to destroy microorganisms, including resistant endospores.

What materials should not be placed in an autoclave?

Materials that are sensitive to high temperatures or moisture.

What is fractional sterilization?

Also called intermittent steaming or tyndallization. It involves repeated heating and cooling over several days.

How does fractional sterilization destroy endospores?

The first heating may not kill endospores. Cooling allows them to germinate into vegetative cells, which are then destroyed during the next heating.

Why might fractional sterilization be used instead of an autoclave?

It may be useful for materials that would be damaged by high-temperature steam, although it can still damage moisture- or temperature-sensitive items.

What is pasteurization?

A heating process used to destroy pathogens in food and beverages without sterilizing the product.

Why is pasteurization not considered sterilization?

It destroys many pathogens but does not necessarily destroy endospores.

What happens to temperature and time during pasteurization?

Higher temperatures require shorter treatment times.

What is UHT pasteurization?

Ultra-high-temperature pasteurization. It heats products to approximately 150°C for a few seconds

What is the purpose of pasteurization?

To reduce pathogens without significantly affecting the flavor, texture, or nutritional value of food.

How does UV radiation control microorganisms?

It damages microbial DNA, preventing normal replication.

Why is UV radiation mainly used on surfaces?

UV light has poor penetrating ability and only affects exposed surfaces

What are examples of UV radiation uses?

Surface disinfection and water treatment plants.

What is ionizing radiation?

High-energy radiation, such as X-rays and gamma rays, that penetrates materials more effectively than UV light.

What are advantages of ionizing radiation?

It penetrates materials, can sterilize food and plastic Petri plates, and does not leave the treated materials radioactive

What is filtration?

A physical method that removes microorganisms from liquids or air rather than killing them.

When is filtration useful?

When materials are heat-sensitive and cannot tolerate heat sterilization.

What is a HEPA filter used for?

Filtering microorganisms and particles from air.

Why does pore size matter in filtration?

Different pore sizes are needed to remove different-sized microorganisms. Some filters remove bacteria and most viruses.

What are the two chemical sterilization exceptions discussed in lecture?

Ethylene oxide and chlorine dioxide.

What is ethylene oxide?

A gas used to sterilize materials that cannot tolerate conventional heat sterilization.

What are the disadvantages of ethylene oxide?

It is explosive and carcinogenic, although it has excellent penetrating abilities.

What is chlorine dioxide used for?

A chemical sterilizing agent available as a gas or liquid. It was used in mailrooms following the 2001 anthrax letter incidents.

How do alcohols control microorganisms?

They denature proteins and dissolve lipids in cell membranes and viral envelopes.

Why are alcohols not effective sterilizing agents?

Endospores are resistant to alcohols.

What are examples of alcohol disinfectants?

Rubbing alcohol and hand sanitizers such as Purell.

What are halogens?

Chemical disinfectants that denature proteins and damage microorganisms.

How does chlorine work?

It denatures proteins and damages cell membranes. Examples include bleach and water treatment.

How does iodine work?

It denatures proteins and works well in combination with alcohol and detergents.

What are phenols?

Chemical disinfectants, also called carbolic acids, that denature proteins and disrupt cell membranes.

What are disadvantages of phenol?

It is toxic and has a strong, pungent odor.

Why are phenolic compounds useful?

Some have lower toxicity while remaining effective disinfectants.

What is the phenol coefficient?

A measurement used to compare the effectiveness of disinfectants against phenol

What does a phenol coefficient greater than 1 mean?

The disinfectant is more effective than phenol under the test conditions.

What are surfactants?

Substances such as soaps and detergents that help remove microorganisms.

How do soaps and detergents control microorganisms?

They mechanically remove microorganisms and emulsify lipids so dirt can be rinsed away.

How can surfactants directly affect microbial cells?

They can damage cell membranes, causing cellular contents to leak out.

What is the filter paper method?

A method used to evaluate chemical antimicrobial agents by soaking filter paper disks in chemicals and placing them on agar containing bacteria.

What is a zone of inhibition?

The clear area around a filter paper disk where bacterial growth has been prevented.

What does a larger zone of inhibition generally indicate?

Greater inhibition of bacterial growth in that test.

Does a larger zone always mean a better disinfectant?

No. Diffusion rate and interactions with other materials can affect the zone size.

What are characteristics of an ideal disinfectant?

Fast-acting, easy to prepare, stable, nontoxic, broad-spectrum, inexpensive, readily available, non-damaging to materials, and without an offensive odor.

Application: You need to sterilize heat-sensitive liquid. Which method should you use?

filtration, because it physically removes microorganisms without exposing the liquid to damaging heat

Application: You need to sterilize dry glassware that tolerates high temperatures. What should you use?

A hot air oven.

Application: You need to sterilize an item that may contain endospores and tolerates heat and moisture. What should you use?

An autoclave at 121°C, 15 psi, for 15 minutes

Application: Someone says disinfecting a laboratory bench makes it sterile. Are they correct?

No. Disinfection reduces microorganisms but does not necessarily eliminate all microorganisms or endospores.

application: A food manufacturer wants to destroy pathogens without changing food quality. What should they use?

Pasteurization.