Lecture #9 Flashcards
What is the effective instrument for pressure-temperature sterilization?
Autoclave
What factors influence antimicrobial agents?
Mode and dosage, number of microorganisms, temperature and pH, kind of microorganisms
Define sterilization.
Destroys/removes all viable microorganisms (including viruses)
What are some agents used for sterilization?
- Heat (autoclave)
- Sterilants (chemical agents capable of destroying endospores)
What is disinfection?
Destroys vegetative pathogens but not bacterial endospores
Name agents used for disinfection.
- Bleach
- Iodine
- Heat (boiling)
What does decontamination/sanitization involve?
Mechanically removes microorganisms to safe levels
List some agents used for decontamination/sanitization.
- Soaps
- Detergents
- Commercial dishwashers
What is antisepsis/degermation?
Reduces microbes on human skin
Give examples of agents used for antisepsis.
- Alcohol
- Surgical hand scrubs
What is the primary goal of any sterilization process?
The destruction of bacterial endospores
What are the primary microbial control methods?
- Physical agents: Heat, radiation
- Chemical agents: Gases, liquids
- Mechanical removal methods: Filtration
What are the most resistant microbial forms?
Bacterial endospores
Define sepsis.
The growth of microorganisms in the blood and other tissues
Primary targets?
Microorganisms causing infection/spoilage
What is sepsis?
The growth of microorganisms in the blood and other tissues
What is asepsis?
Any practice that prevents the entry of infectious agents into sterile tissues
What are aseptic techniques?
Practiced in health care; range from sterile methods to antisepsis
What are antiseptics
- chemical agents applied directly to exposed body surfaces (skin and mucous membranes), wounds, and surgical incisions to prevent vegetative pathogens
- have microbistatic
What are some examples of when antiseptics would be used?
- Preparing the skin before surgical incisions with iodine compounds
- Swabbing an open root canal with hydrogen peroxide
- Ordinary hand washing with a germicidal soap
What does stasis and static mean?
“to stand still”
What does ‘bacteristatic’ mean?
Chemical agents that prevent the growth of bacteria on tissues or on objects in the environment
What is fungistatic?
chemicals that inhibit fungal growth
True or False: A -cidal agent always results in sterilization.
False
What are critical medical devices?
Devices that contact sterile tissues and must be sterilized
What defines semicritical devices?
Devices that contact mucosal membranes and require high-level disinfection, preferably sterilized
What are noncritical devices?
- Devices that do not touch the patient or only touch intact skin
- low level disinfection unless contaminated with blood/body fluids
Substances that require sterilization
durable solids (rubber) to sensitive liquids (serum)
Consideration for sterilization
- cost
- effectiveness
- methods of disposal
What is the microbiological definition of death?
Permanent termination of an organism’s viral processes including loss of reproductive capability, even under optimum growth conditions
Describe the death of a microbial population.
Occurs in a logarithmic manner, no instantaneous death
Active cells
die more quickly
What factors affect the death rate of microorganisms?
- Number of microbes
- Nature of microorganisms
- Temperature and pH
- Concentration of agent
What are the modes of action of antimicrobial agents?
- Least selective agents: Effective against a wide range of microbes
- Selective agents: Target a single cellular component
What are common cellular targets for antimicrobial agents?
- Cell wall
- Cytoplasmic membrane
- Cellular synthetic processes (DNA, RNA)
- Proteins
Elevated temperatures are often
microbicidal
Lower temperatures are often
microbistatic
What is the effect of moist heat on microorganisms?
Operates at lower temperatures, coagulation and denaturation of proteins
What is the effect of dry heat on microorganisms?
dehydrates cell, denatures proteins
Bacterial endospores
- Exhibit greatest resistance
- Destruction of spores requires temperatures above boiling
Vegetative cells
- Vary in sensitivity to heat
- Death times vary from 50 ℃ for 3 minutes to 60 ℃ for 60 minutes
What is the difference between thermal death time (TDT) and thermal death point (TDP)?
- TDT: Shortest time to kill all microbes at specified temperature
- TDP: Lowest temperature to kill all microbes in 10 minutes
Moist heat methods
- boiling water
- pasteurization
- steam under pressure (autoclaving)
Boiling water
Disinfection, not sterilization because 100 ℃ will not kill all resistant cells
What is pasteurization?
Disinfection of beverages by applying heat to kill potential agents of infection and spoilage while retaining flavor and nutritional value
Steam under pressure (autoclaving)
- 15 PSI above normal (a total of 2 atmosphere)
- 121 ℃
Incineration
Flame reduces microbes to ashes and gas
Hot air oven
Sterilization at 150°C to 180°C for 2 to 4 hours to ensure destruction of endospores
What is the purpose of cold treatment in microbial control?
Slows growth and retards activities of microbes
What temperature range can cultures of bacteria, viruses and fungi be preserved for long periods?
-70 ℃ to - 135 ℃
What is desiccation?
Dehydration of vegetative cells directly exposed to normal room temperature
What is lyophilization?
Combination of freezing and drying
What is ionizing radiation?
Gamma rays, X rays used for sterilizing materials sensitive to heat or chemicals
What is nonionizing radiation?
Ultraviolet rays that are most lethal from 240 to 280 nm (with a peak at 260 nm)
What is the function of filtration in microbial control?
Removes microbes from air and liquids
what are the uses of filtration?
Prepare liquids that cannot withstand heat such as serum, blood products, vaccines, drugs, IV fluids, enzymes, and media
What does osmotic pressure do to bacteria?
Creates a hypertonic environment by adding salt and sugar, causing plasmolysis
Methods of chemical control
- Aqueous: Chemicals dissolved in pure water as the solvent
- Tinctures: Chemicals dissolved in pure alcohol or alcohol-water mixtures
What are desirable qualities in a germicide?
- Rapid action
- Solubility in water or alcohol, long term stability
- Broad-spectrum microbicidal action without toxicity
- Penetration of inanimate surfaces, cumulative or persistent action
- Resistance to becoming inactivated by organic matter
- Non-corrosive and non-staining
- Sanitizing and deodorizing properties
- Affordability and availability
What are high-level germicides?
Kill endospores and can be used as sterilants
What are intermediate-level germicides?
Kill fungal but no bacterial, spores, resistant pathogens, viruses
Low-level germicides
Eliminate vegetative bacteria, vegetative fungal cells, some viruses
factors affecting germicidial activity
- Nature of microorganisms being treated
- Nature of material being treated
- Degree of contamination time of exposure
- Strength and chemical action of germicide
What is the mode of action of halogens like chlorine?
Denature enzymes permanently and suspend metabolic reactions
What do oxidizing agents do?
Kill endospores and all other microbes by forming free radicals
How do aldehydes disrupt microbial activity?
Irreversibly disrupt the activity of enzymes and other proteins within the cell
What is the mode of action of phenols?
Disrupt cell walls and membranes, proteins
What is the action of detergents on microbes?
Disrupt the cytoplasmic membrane, causing cell death
How do heavy metal compounds exert microbial effects?
Bind onto functional groups of proteins and inactivate them
What is the effect of acids and alkalis on microbes?
Alter pH, affecting microbial growth
