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
