Physical Means of Controlling Microbial Growth Flashcards
- Removes particles less than 3um and greater than 10um in size with 99.9% efficiency, but does not ensure sterilization
- Used in clean rooms: quarantine, biological safety labs
High-efficiency particulate air (HEPA) filter (disinfection)
Practice of using chemical agents used on body surfaces to safely reduce microbial numbers
Antisepsis
Methods of heat sterilization
- Dry heat
- Moist heat
Thermal death time determines
Heat sensitivity of microorganism
Food-related factors that may affect heat sensitivity of endospores
- Low acidic pH kills microorganisms faster
- High sugar, protein, or fat content decreases heat penetration
- Effect of salt conc. is species specific
Endospores must be exposed for a (blank) period of time and (blank) temp. when using dry heat
longer, higher
True or false. UV light is limited to disinfecting exposed surfaces only.
True.
Which kills in autoclaving, temperature or pressure?
Temperature
True or false. Sanitization is less effective than disinfection. Because of this, it is not safe for food contact surfaces.
False. It is safe and does not involve toxic levels of anti-microbial agents.
- X-rays and gamma rays
- Produces high reactive molecules that can destroy DNA, lipids, and proteins
Ionizing radiation (sterilization)
Most accessible and widespread method of controlling microbial growth
Heat sterilization
- Prevents spoilage and preserves food by decreasing microbial growth rate
- Does not kill microorganism
Refrigeration and freezing
Factors that affect efficacy of disinfection
- Nature and no. of cells
- Type and conc. of disinfectant
- Type and condition of surface to be disinfected
- Duration of exposure
Serves to reduce the no. of microorganisms to a safe hygienic level
Sanitization
- Subjects milk in 74°C -> 140°C -> 74°C in less than 5 mins.
- Allows milk to be stored in room temp. for 1-3 months
Ultra-high temperature (UHT) (sterilization)
Simplest method of decontamination, temperature at 100°C kills most pathogenic organisms
Boiling (disinfection)
- Non-ionizing radiation
- Uses wavelengths that cause mutations in microbial DNA that result to death
- May be ineffective bc of light activated repair mechanisms
UV Radiation
Use of conduction, usually at 170°C for 1 hr, 160°C for 2hrs
Hot air convection oven (sterilization)
- Made of high tensile-strength polymers with numerous microscopic pores
- Used with a syringe and sterile collecting vessel; acts like a sieve to trap particles
Liquid filtration via membrane filters (sterilization)
Completely eliminates all viable microorganisms, including endospores
Sterilization
Use of open flame
Flame-sterilization (sterilization)
True or false. Relationship of (D) with time is exponential.
True.
- Used for milk and heat-sensitive liquids
- Does not kill all, only reduces microbial load
- Increases shelf life of perishable liquids
Pasteurization (disinfection)
- Water from frozen materials are drawn out in a vacuum
- High-quality products viable for years
Freeze-drying (lyophilization)
Eliminates nearly all recognized pathogens but not necessarily all microbial forms (eg. endospores)
Disinfection
Practice of rendering an area or objects safe to handle by inactivating or reducing contaminants to an acceptable level
Decontamination (Decon, Decontam)
Uses combustion to destroy organic matter; waste disposal
Incineration (sterilization)
Amount of time it takes to reduce a bacterial population 1-fold
Decimal reduction time (D)
Pathogenic bacteria that pasteurization can kill
- E. coli O157:H7 (causes hemorrhagic diarrhea)
- Listeria monocytogenes
- Campylobacter spp.
Absence of water inhibits enzymatic activities
Dying (Desiccation) [Eg. yeast, dried fruit, etc.]
True or false. Endospores do not survive after boiling.
False. They do.
- Controlled milk flow rate through a tube
- Heats milk at 71°C for 15s then cooled
Flash pasteurization (disinfection)
Fibrous sheet made of overlapping paper or glass fibers that trap particles
Air filtration via depth filters
Lethal dose of Gy for humans
10Gy
Factors that need to be considered when using heat sterilization
- Nature of the microorganism
- Sensitivity to heat
- Duration of the heat treatment
Time it takes to kill all cells with a gvien temp.
Thermal death time
Probability of a microorganism surviving in sterilization
One in a million
Absorbed radiation dose per gram of tissue
Grays (Gy)
Uses steam coupled with pressure to kill microorganisms including endospores
Autoclaving (sterilization)
Conditions of autoclaving
121°C, 15 psi, 15-20 mins.
- Non-ionizing radiation
- Uses wavelengths that cause mutations in microbial DNA that result to death
- May be ineffective bc of light activated repair mechanisms
UV Radiation
Examples of antiseptics
Iodine in betadine, antibacterial soap, hydrogen peroxide, alcohol
(D) is dependent on the following:
- Duration
- Temperature
Slow heating and penetrating, sterilize objects and glassware (eg. flame-sterilization, hot air, convection ovens, incineration)
Dry heat
Thin polycarbonate film that is irradiated and chemically etched to yield uniform holes
Nucleopore filter
Decimal reduction time of endospores
121°C for 4-5 mins
Decimal reduction time of vegetative cells
65°C for 0.1-0.5 mins.
Faster heating and steam penetration, less (D) values - kills microorganisms faster (eg. boiling, autoclaving, pasteurization)
Moist heat
