Micro Exam-2 Ch. 7 Flashcards
Sterilization
Removing and destroying all living microorganisms
Disinfection
Destroying harmful microorganisms
Sanitization
Lowering microbial counts to safe public health levels
Degerming
Mechanical removal of microbes from a limited area
Antisepsis
Destroying harmful microorganisms from living tissue
Biocide/germicide
Treatments that kill microbes
Bacteriostatic
Inhibiting, not killing, bacteria
Sepsis
From the Greek for decay or putrid, refers to bacterial contamination
Asepsis
Absence of significant contamination
-cital
killing organism
-static
inhibiting growth
When microorganisms are heated or treated with Antimicrobial agent they usually die at
a constant rate
Effectiveness of treatment for microbes depends on
- Number of microbes
- Environment (organic matter, temperature, biofilms)
- Nature of medium (fat, proteins protect)
- Time of exposure
- Microbial characteristics
Actions of Microbial Control Agents
-Alteration of membrane permeability
Damages lipids or proteins of the plasma membrane
Interrupt nutrient exchange, leaks cellular contents
Interferes with the growth of the cell
Actions of Microbial Control Agents
-Damage to proteins (enzymes)
Heat or chemicals damage structural bonds
Denature proteins
Actions of Microbial Control Agents
-Damage to nucleic acids
Damage to DNA and RNA effects cell replication and other metabolic functions
Actions of Microbial Control Agents
- Alteration of membrane permeability
- Damage to proteins (enzymes)
- Damage to nucleic acids
Moist heat (Boiling, steam)
denatures proteins/enzymes
Dry heat (Flaming, Incineration, Hot-air)
– Kills by Oxidation
• Steam under pressure
(Autoclave; temp above boiling water): Reliable sterilization
• Autoclave:
steam under pressure 100 (0),110 (5), 116 (10), 121 (15), 126 (20), 135C (30 psi) 121C at 15 psi for 15 min Kills all organisms and endospores Steam must contact the item's surface
Time is variable during sterilization depends on
size of glassware ect.
Pasteurization
reduces spoilage organisms and pathogens
Pasteurization reduces spoilage organisms and pathogens
- Mild heat treatment- Use mild heat treatment to kill pathogens and organisms-MILK
- Thermoduric organisms survive
- Dairy industry: Alkaline phosphotase test-APS
Pasteurization- Low temperature long time (LTLT):
63 degree C for 30 mins
Pasteurization- High-temperature short-time (HTST): also known as FLASH Pasteurization
72C for 15 sec
Pasteurization- Ultra-high-temperature (UHT):
140C for 4 sec
Differences can be expressed in terms of:
Thermal death point (TDP)
Thermal death time (TDT)
Decimal reduction time (DRT, D-value)
Thermal death point (TDP):
lowest temperature at which all cells in a liquid culture are killed in 10 min
Thermal death time (TDT):
minimal time for all bacteria in a liquid culture to be killed at a particular temperature
Decimal reduction time (DRT, D-value)
Used to express bacterial heat resistance Minutes to kill 90% of a population at a given temperature-
D-value is always represented in minutes
THIS WILL BE ON TEST
Filtration
• Passage of a liquid or gas through a screenlike material
• Used for heat-sensitive materials
Eg: some culture media, enzymes, vaccines, and antibiotics
• High-efficiency particulate air (HEPA) filters- in BSL-3 & BSL-4
remove microbes >0.3 µm
• Membrane filters
remove microbes >0.22 µm
Low temperature
Provides bacteriostatic effect
• Refrigeration
• Deep-freezing
High pressure
Denatures proteins
Desiccation:
absence of water prevents metabolism
Microbes cannot grow or reproduce but remain viable for years
Lyophilization or freeze drying is an example
Osmotic pressure:
uses salts and sugars to create hypertonic environment; causes plasmolysis (i.e., water leave the microbial cell)
Ionizing radiation
(X rays, gamma rays, electron beams)
• Shorter wavelength (<1 nm)
• Ionizes water to create reactive hydroxyl radicals (ROS)
• Damages DNA by causing lethal mutations
Nonionizing radiation
- UV (270 nm) –Germicidal lamp
* Damages DNA by creating thymine dimers which inhibit correct replication
Microwaves
kill by heat; not especially antimicrobial
Chemical agents
- Used for control the growth of microbes on both living tissue and inanimate objects
- Sterility levels varies depending on chemical agent
- Selection of suitable agent is key
- Use-Dilution Tests (AOAC standard)
- Metal or glass cylinders (8 mm x 10 mm) are dipped in test bacteria and dried
- Cylinders are placed in disinfectant for 10 min at 20C
- Cylinders are transferred to culture media to determine whether the bacteria survived treatment
