Physical Means of Controlling Microbial Growth Flashcards
- making area/object safe to handle by inactivating/reducing contaminants to an accceptable level
- general term
Decontamination
- completely eliminates all viable microorganisms, including most resistant forms
- probability of a microorganism surviving is < 1/1,000,000
- you’re pretty sure wala lang bacteria
- ex. autoclaving
Sterilization
- less lethal than sterilization
- eliminates all pathogens, but not necessarily all microbial forms (endospores)
Disinfection
List
What factors impact the efficacy of disinfection?
4
- Nature & Number of cells
- Type & concentration of disinfectant
- Type & condition of surface to be disinfected
- Duration of exposure
- reduce number of microorganisms to a safe hygienic level
- less effective than disinfection
- safe for food contact
Sanitization
- using antiseptics to reduce/eliminate microorganisms in and on the body
Antisepsis
chemical agent used on body surfaces to safely reduce microbial numbers
Bonus: Give an example
Antiseptic
Iodine in Betadine, antibacterial soap, hydrogen peroxide, rubbing alcoh
List
Physical Methods of Growth Control
3
- Heat
- Radiation
- Filtration
- most accessible and widespread method of controlling microbial growth
- has to take into account the nature of the
microorganism, its sensitivity to heat, and the duration
of the heat treatment.
Heat Sterilization
the minimum, optimum, and maximum temperatures
that determine the growth of a microorganism.
cardinal temperature of microorganisms
What happens to a microorganism when exposed to its minimum/optimum/maximum growth temperature?
Why does that happen?
Minimum
- activities are essentially frozen bc lack of energy → growth stops
Optimum
- fastest growth bc it’s the best thermal conditions for met activities
Maximum
- microbial growth stops bc denatured enzymes can’t do activities
What measurements can we use to determine the effectiveness of sterilization methods?
2
- Decimal reduction time (D)
- Thermal death time
- Amount of time it takes to reduce a bacterial population 10—fold
- Dependent on duration and temperature
- Use to determine how sterilization methods are effective at reducing microbial numbers
Decimal reduction time (D)
- Time it takes to kill all cells with a given temperature
- Determines heat sensitivity of the microorganism
Thermal death time
For heat sterilization, the relationship between decimal reduction time and temperature is ____, and as you can see it, is dependent on the ____ of the treatment and the ____ being used.
logarithmic, duration, temperature
How do we categorize the methods of heat sterilization?
2
- Dry heat
- Moist heat
Differentiate dry & moist heat methods
3
(Dry vs Moist)
- no water vs with water
- heating & penetration (slow vs fast)
- sterilize objects & glassware vs kills microorganisms faster (less D value)
List examples of dry heat.
What is used in each example?
3
Flame-sterilization
* Use of open flame
Hot air convection oven
* Use of conduction as hot air circulates and heats up the objects in the chamber.
* 70ºC for 1 hr, 160ºC for 2 hrs (↑ temp & ↑ durations)
Incineration
* Uses combustion to destroy any organic material in a sample → ash
all sterilization
- Use of open flame
- sterilize objects (wire loops, forceps, glass slides)
- prevent cross-contamination between microbial samples.
Flame-sterilization
- Use of conduction
- hot air circulates and heats up the objects in the chamber.
- 70ºC for 1 hr, 160ºC for 2 hrs
- ↑ temp & ↑ durations
Hot air convection oven
- Uses combustion to destroy any organic material in a sample
- turns into ash
Incineration
What PH laws prohibit incineration?
Philippine Clean Air Act of 1999
Ecological Solid Waste Management Act of 2000
Moist heat examples
What do they use?
Boiling
* heats water to 100ºC
Autoclaving
* uses steam & pressure
Pasteurization
* uses milk & heat-sensitive liquids
- simple disinfection
- heats water to 100ºC
- kills most pathogenic organisms
- but endospores (& other heat-resistant structures) survive
Boiling
T/F
Boiling is an effective sterilization method.
F - disinfection method only
- Uses steam coupled with pressure to kill microorganisms, including endospores
- Pressure within the chamber → ↑ latent heat of vaporization of water, → ↑ temp of steam in autoclave → kill even heat-resistant structures.
- It is the temperature (and not the pressure) that kills
- Conditions: 121ºC, 15 psi, 15- 20 mins
Autoclaving
What are the conditions when autoclaving?
121ºC, 15 psi, 15- 20 mins
How does an autoclave kill heat resistant structures?
- Chamber has pressure
- ↑ latent heat of vaporization of water
- ↑ temp of steam in autoclave
- RIP even heat-resistant structures
- Disinfection
- Used for milk and heat sensitive liquids
- only reduces microbial load
- Does not kill all microorganisms
- Increases shelf life of perishable liquids
- Kills pathogenic bacteria
Pasteurization
Examples of Pasteurization
(2)
What are the conditions for each?
Flash Pasteurization (disinfection)
* Controlled milk flow rate through a tube
* Heats milk at 71ºC for 15s then cooled
* most common method used to pasteurize milk
Ultra-high temperature (UHT) (sterilization)
* 74ºC → 140ºC → 74ºC in less than 5 seconds
* rapid heating sterilizes the milk, can be stored at room temp for 1-3 months
Differentiate
Decimal reduction time (D) of endospores vs vegetative cells
- Endospores: 121ºC @ 4-5 mins
- Vegetative cells: 65ºC @ 0.1-0.5 minutes
List
Food-related factors that may affect heat sensitivity of endospores
3
How does it impact endospores?
- Low acidic pH kills microorganisms faster
- High sugar, protein, or fat content decreases heat penetration → slower reduction times
- Salt concentration - species specific
Fill in the blank
If dry heat is used, the endospores must be exposed for a [longer/shorter] period and a [lower/higher] temperature to successfully
eliminate them.
longer, higher
Disinfection/Sterilization
- Flame sterilization
- Hot air convection oven
- Incineration
- Boiling
- Autoclaving
- Flash Pasteurization
- Ultra-High Temperature Pasteurization
- S
- S
- S
- D
- S
- D
- S
Filtration is best for ____.
heat-sensitive liquids and gases
Examples of filtration
Bonus: via what?
- Air filtration via depth filters
- Liquid filtration via membrane filters
- Nucleopore filter
- fibrous sheets made of overlapping
paper or glass fibers that trap air particles - Ex. High-efficiency particulate air (HEPA) filter [disinfection]
depth filter
when circulating air is decontaminated through depth filters
air filtration
- Removes particles 3μm < particle < 10μm
- Disinfection: 99.9% efficiency, but does not ensure sterilization
- Used in clean rooms: quarantine, biological safety laboratories
- also used inside biosafety cabinets, to make sure air doesn’t contaminate the samples being worked on by researchers.
High-efficiency particulate air (HEPA) filter
Size of particles that HEPA filter removes
< 3μm, > 10μm
- Used in liquid filtration (sterilization)
- Made of high tensile-strength polymers w/ numerous microscopic pores
- Used with a syringe and sterile collecting vessel; acts like a sieve to trap particles
- Filters are attached to a syringe holding liquid to be sterilized. By pushing the liquid out of the syringe and into a sterile collecting vessel, the filter acts like a sieve that traps particles, leaving you with a sterile liquid in the collecting vessel.
membrane filters
How does a membrane filter work?
- Filters are attached to a syringe holding liquid to be sterilized.
- Liquid is pushed out of the syringe and into a sterile collecting vessel
- Filter acts like a sieve that traps particles
- Result: sterile liquid in the collecting vessel.
- Thin polycarbonate film
- irradiated and chemically etched to yield uniform holes
- often used to isolate specimens for observation under a scanning electron microscope.
Nucleopore filter
Sterlization/Disinfection
- Air filtration (HEPA filter)
- Liquid filtration via membrane filters
- D
- S
Classifications of radiation
non-ionizing or ionizing
- Disinfection
- 220-300nm wavelengths
- Causes mutations in DNA that results to microbial death
- May become ineffective because of activated repair mechanisms that fix their UV-damaged DNA.
- Limited to disinfecting exposed surfaces only
UV radiation
wavelengths that UV light uses
220 - 300 nm
- sterilization
- X-rays and gamma rays
- Produces highly reactive molecules that can destroy DNA, lipids, and proteins, leading to cell death
- Used to sterilize medical equipment and food products in large industrial companies
Ionizing radiation
What is Grays (Gy)?
Lethal dose for humans?
- absorbed radiation dose per gram of tissue
- Lethal dose for humans is 10Gy.
- Endospores can resists up to 3,300Gy
- The measure for the amount of radiation needed to kill an organism
Sterlization/Disinfection
- Non-Ionizing Radiation
- Ionizing Radiation
- D
- S
Food Preservation Methods
2
- Low temperatures
- Dehydration
How do low temperatures preserve food? At what temperatures?
- Prevents spoilage and preserves food by decreasing microbial growth rate
- Decreases amount of energy available to enzymes
- Does not kill the microorganism
- Refrigeration (~5ºC) and freezing (~ -20ºC)
Kinds of dehydration
Drying
Freeze-drying (lyophilization)
How does drying preserve food?
- Absence of water inhibits enzymatic activities
- Drying and dessication remove water from food products → preventing microbial growth
- Ex.: Yeast, dried fruit, etc.
How does freeze-drying preserve food?
- Water from frozen materials are drawn out in a vacuum
- Produces High-quality products viable for years
- Food sent into space as rations for astronauts
