Ch.5 Flashcards
sterilization
- removal or destruction of all microorganisms and viruses
– Sterile item is free of microbes including endospores, but does not consider prions
What does the suffix “-cidal” mean?
- of or relating to killers or the act of killing
- Germicidal chemicals can disinfect and sterilize
pasteurization
brief heating to reduce number of spoilage organisms, destroy pathogens without changing characteristics of product
How does pasteurization work?
- Pasteurization destroys heat-sensitive pathogens, spoilage organisms
– High-temperature–short-time (HTST) method
–> Example: milk is heated to a specific temperature for a set period of time to kills harmful bacteria
Is pasteurization used to sterilize food products?
- Pasteurization cannot eliminate all microorganisms and spores
- Pastuerized food has to be kept cold
Why is handwashing with plain soap and water useful in controlling the spread of microorganisms?
- Washing and scrubbing with soaps and detergents achieves routine control
- Soap aids in mechanical removal of organisms
- Beneficial skin microbiota reside deeper on underlying layers of skin, hair follicles
- Not adversely affected by regular washing
What are the 4 ways in which food is treated to prevent spoilage and to eliminate disease?
- Chemical preservatives
- Prevent or slow microbial growth and extend shelf life
- Food preservatives must be non-toxic for safe ingestion - Weak organic acids (benzoic, sorbic, propionic)
- Affect cell membrane function
- Control molds and bacteria in foods - Nitrate and nitrite used in processed meats
- Inhibit endospore germination and vegetative cell growth
- Stops growth of Clostridium botulinum
- Higher concentrations give meats pink color - Low-Temperature Storage
- Refrigeration inhibits growth of pathogens and spoilage organisms by slowing or stopping enzyme reactions
- Psychrotrophs, psychrophilic organisms can still grow - Freezing preserves by stopping all microbial growth
- Some microbial cells killed by ice crystal formation, but many survive and can grow once thawed
Which 4 factors affect the microbial death rate?
- temperature
- osmotic pressure
- pH
- oxygen concentration
How does Moist heat Kill Microorganisms?
- irreversibly denatures proteins
Why boiling NOT a reliable form of sterilization?
- Does not sterilize: endospores can survive
- boiling destroys most microorganisms and viruses
What is a common application of dry heat that we use in microbiology labs?
- Incineration (destruction by burning) oxidizes cell components to ashes.
– In microbiology laboratories, the wire loops continually reused to transfer bacterial cultures are sterilized by flaming or heating in a benchtop incinerator
– Incineration is also used to destroy medical wastes and contaminated animal carcasses.
What is the best way to go about sterilizing heat-sensitive liquid media?
- Membrane filtration in a liquid medium, retains bacteria while allowing the fluid to pass through.
- Used extensively to remove organisms from heat-sensitive fluids
- Membrane filters or microfilters
– Small pore size to remove bacteria
– Vacuum used to move fluid through filter - Depth filters
– Thick porous filtration material (for example, cellulose)
– Electrical charges trap cells
HOW does UV radiation destroy bacteria?
- Ultraviolet radiation destroys microbes directly
– Damages DNA
– Used to destroy microbes in air, water, and on surfaces
– Poor penetrating power
— Thin films or coverings can limit effect
— Cannot kill microbes in solids or turbid liquids
— Most glass and plastic block rays
– Must be carefully used since damaging to skin, eyes
Microwaves do NOT directly kill organisms. How do microwaves kill?
- Microwaves do not affect microorganisms, but the heat they generate can be lethal
– Microwave ovens heat food unevenly, so cells can survive
chemical germicides
- Germicidal chemicals can disinfect and, in some cases, sterilize.
- React irreversibly with proteins, DNA, cytoplasmic membranes, or viral envelopes.
- Less reliable than heat but useful for treating large surfaces and heat-sensitive items.
– Some are sufficiently non-toxic to be used as antiseptics
Sterilants
Category of germicidal chemicals
destroy all microbes; also called sporocides
- Heat-sensitive critical instruments
High-level disinfectants
Category of germicidal chemicals
destroy viruses, vegetative cells
- Do not reliably kill endospores
- Semi-critical instruments
Intermediate-level disinfectants
Category of germicidal chemicals
destroy vegetative bacteria, mycobacteria, fungi, and most viruses
- Disinfect non-critical instruments
Low-level disinfectants
Category of germicidal chemicals
destroy fungi, vegetative bacteria except mycobacteria, and enveloped viruses
- Do not kill endospores, non-enveloped viruses
- Disinfect furniture, floors, walls
What are the 4 factors that must be considered when selecting a germicidal chemical?
- Toxicity: benefits must be weighed against risk of use
- Activity in presence of organic material
- Compatibility with material being treated
- Liquids cannot be used on electrical equipment 4. Residues - can be toxic or corrosive - Cost and availability
- Storage and stability
- Concentrated stock decreases storage space - Environmental risk
- Agent may need to be neutralized before disposal
Are Prions easily destroyed by common sterilization procedures?
No
Does the quantity of starting bacteria affect how fast it takes to kill them all?
- No
- The time it takes to kill bacteria is not dependent on the initial number of bacteria
