Chapter 5 Flashcards
Sterilization
Process of destroying all microorganisms (including endospores) or viruses within or on a product.
Does sterilization remove prions
No, because they are hard to get rid of, heat-resistant, would need to be targeted individually
Sterilant
chemical that removes all microbes
Disinfection
Product that kills microorganisms or viruses within or on product, but SOME microbes may remain
Disinfectant
chemical used to destroy MOST microbes on an inanimate object
Types of Disinfectants
"cide" = treatments that kill "static" = treatments that inhibit rather than kill
Germicide
a disinfectant that kills microorganisms & viruses
Bactericide
a disinfectant used to kill vegetative forms of bacteria, but not usually endospores
Fungicide
a disinfectant used to kill fungus
Virucide
a disinfectant used to kill viruses
Bacteriostatic or fungistatic agent
chemical or condition that prevents growth of bacteria/fungus, but does not kill them
Antiseptic
Chemical that is non-toxic enough to be used on human tissue
- Used for cleaning skin surfaces, such as hands and wounds, and as prep for surgery
- Kills or decreases microbes
- Does not destroy endospores
Decontamination
- process that reduces the number of microbes to a safe level
- may kill, inactivate or remove microorganism, viruses and any toxins that may be present within or on the product
- important in the food industry, decontamination of an area or product to meet public health standards
Sanitizer
chemical used to decontaminate.
Factors relating to antimicrobial action
Time of contact # of microbes Temperature/pH D value Chemical concentration Type of microbe Extraneous materials
Time of Contact
- Death of microbe is not always instantaneous
- Only a fraction of microbes are killed in a certain period of time
- May take 12 or more hours to destroy most or all of the bacteria growing on an object
Number of microbes
- Death of a population of bacteria is related to the number of cells present
- The greater the number of cells on a surface, the greater amount of time is needed to disinfect that surface
D value
Decimal reduction time
= time to kill 90% of bacteria present
- D value is usually constant
D value example
if D= 2 minutes, then a population of 100 would be reduced to 10 in 2 minutes and to 1 in 4 minutes.
Shows the time of contact and number of microbes affect the action of the disinfectant
Temperature and pH
- Chemical disinfectants usually work better at higher temperatures
- most disinfectants are designed to work near room temp.
- disinfectants also have optimum pH range, but this varies for chemical type
- If temperature of pH is not optimum, the time of contact must be increased
Concentration of Chemical disinfectant
- Mostly, more concentrated disinfectant = shorter killing time
- at lower concentration are bacteriostatic
- at higher concentration are bactericidal
Types of microbes
Least resistance
Moderate resistance
Highest resistance
Least resistance microbes
vegetative forms of most bacteria and viruses with membranes
Moderate resistance microbes
- Mycobacterium tuberculosis
- Staphylococcus aureus
- Pseudomonas species
- Naked viruses
Mycobacterium tuberculosis facts
Acid fast positive d/t mycolic acid in cell wall being stained by phenol
staphylococcus aureus facts
clumping factor, capsule, Gram -
Pseudomonas species facts
Gram -, biofilms, low nutrition requirements
Highest resistance microbes
Bacterial endospores (Clostridium and bacillus)
Why are endospores so hard to kill
dipcolenic acid to keep moisture away from DNA in endospore. Super resistant to heat and chemicals.
Peptidoglycan helps protect as well
Presence of extraneous matter
- Soil, blood, pus
- organic matter may react with disinfectant and cause them to be less effective
- Therefore recommended to clean surface before using disinfectant
Effectiveness of microbial control
High effectiveness
Intermediate effectiveness
Low effectiveness
High effectiveness
kills ALL organisms including endospores. Sterilization!
Intermediate effectiveness
kills “moderate resistant” pathogens
ex. mycobacterium tuberculosis, staph aureus, pseudomonas, naked viruses
Low effectiveness
kills vegetative bacteria and enveloped viruses
Mode of Action
- Adverse effect on microbe - how it kills or harms
- some methods of microbial control are general and destroy or alter many structures
- some methods are very specific to certain portion of bacterial cell or virus
- Targets: synthesis and structure of cell, cell membrane, proteins, and nucleic acid
Cell wall and cell membrane
mode of action target
- Synthesis of cell wall disrupted or cell wall is digested after it is synthesized. Weak cell wall exposes microbe to environment and can lead to lysing.
- Cell membrane damaged so it is “leaky” (no longer selectively permeable)
- molecules can enter and exit cell easily
Proteins
mode of action target
- Synthesis of proteins stopped when antimicrobial agent…
1. binds to ribosome - prevents translation
2. binds to DNA - prevents transcription - protein function altered when antimicrobial agent binds to protein and alters protein shape (denaturation)
- So also affects metabolic processes if enzymes are target
Nucleic Acids
mode of action target
- DNA synthesis may be stopped when antimicrobial agent causes mutations. ex. Thiamine dimers
- If DNA synthesis is affected then protein synthesis may also be affected
3 possible outcomes of mutations
- Beneficial
- Death
- Unchanged or no change
Chemical methods of microbial control
- Over 10,000 types of chemical control.
- Different types used in hospital: Alcohol, Hydrogen peroxide, Surfactants, Heavy metals, Phenol (carbolic acid), ethylene oxide, chlorine and iodine
effectiveness of ALCOHOL
-Low effectiveness
Action of ALCOHOL
disrupts cell membranes, denatures cellular proteins, do not destroy endospores
Concentration of ALCOHOL
exception: should be diluted to 75% to dissolve proteins first
Contact time of ALCOHOL
limited because of quick evaporation
Types of ALCOHOL and toxicity to humans
- Ethyl (ethanol, grain) - non-toxic- more expensive (hand sanitizer)
- Isopropanol (rubbing) - more effective, but more toxic to animals - vapors can cause damage to CNS
HYDROGEN PEROXIDE effectiveness
low
Toxicity of HYDROGEN PEROXIDE to humans
None
Action of HYDROGEN PEROXIDE
large amounts overwhelm catalase and peroxidase in cell
Surfactants
surface-active agents, detergents = reduce surface tension of water and allow organics to dissolve easily
Anionic (soap)
action and effectiveness
does not kill (“no effectiveness”) but removes microbes. Creates micelle, surrounding dirt
Cationic (quaternary ammonium compounds or quats)
action and effectiveness
- low effectiveness (ineffective for Gram - bacteria)
- ## ADBAC
Toxicity of surfactants to humans
low to none
pH of cationic vs anionic
Cationic = basic anionic = acidic
Heavy metals
Mercury - metaphen/nitromersol
Silver - silver nitrate (newborns now given erythromycin), silver sulfasiazine (for burns)
Effectiveness - low
Toxicity of heavy metals to humans
toxic if used on exposed tissue, so used only topically (“topical antiseptic”)
Action of heavy metals
denatures proteins, binds to sulfur containing proteins
Phenol and derivatives effectiveness
intermediate, often ineffective against naked viruses
phenol and derivatives toxicity
very toxic, used at topical antiseptic, dilute forms used in Lysol, triclosan
action of phenol and derivatives
damages cell membranes, denatures enzymes
Who used phenol as one of the first disinfectants
Lister
Ethylene Oxide effectiveness
High (endospores and viruses)
Toxicity of Ethylene oxide
high, carcinogen
Action of Ethylene oxide
- usually in gas form, explosive
- slow acting (up to 18 hours in special chamber)
- used for heat or moisture sensitive items
- mutagen, requires aeration of product before use
Effectiveness of chlorine and iodine
intermediate
Toxicity to humans of chlorine and iodine
slightly toxic, irritating to tissues, possible carcinogen
Action of chlorine and iodine
denatures proteins and DNA
iodine combined with alcohol is called
tincture
iodine + detergent =
iodophore
less irritating and do not stain, can be contaminated with Pseudomonas species
Bleach
sodium hypochlorite
Hand cleansing soap and water
removes extraneous matter and microorganisms
Hand cleansing with antibacterial soap
triclosan (contains phenol)
Hand cleansing with hand sanitizers
alcohol
Physical methods of microbial control
- Dry heat
- Moist heat
- Autoclave
- Harvey chemiclave
- Radiation - UV and ionizing
- Filtration
Dry Heat
- incineration of contaminant in hot oven or direct flame
- Bunsen burner
- Sterilize glassware, powders, oil
Disadvantage of dry heat
time - destruction of endospores would require 150-180 C for 2-4 hrs, which would burn up most materials
Moist heat
- boiling or steaming kills vegetative forms, denatures proteins
- boiling water = 100C
Disadvantages of moist heat
- some microbes can tolerate short boiling times
- endospores survive several hours of boiling
- Greatly reduces number of bacteria, but does not sterilize
pasteurization
Flash method
Holding method
Ultra
Flash method
pasteurization
high temp (72C) for short time (15 seconds) as liquid is in pipes is common method
Holding method
pasteurization
lower temp (63C) for longer time (30 mins) - treated in bulk
Ultra
pasteurization
high temp (140) for shorter time ( a few seconds)
Autoclave
moist heat under pressure
- when water is present, all macromolecules are denatures at relatively low temperatures
- Steam under 15 psi pressure can reach temperature of 121C which will kill even endospores after 15 minutes
Disadvantage of autoclave
some items can be damaged by water and heat
Harvey Chemiclave
- Alcohol or formaldehyde vapor is pressurized and heated
- used for dental instruments
disadvantages of Harvey Chemiclave
more expensive that autoclave, but does not require drying time
-Some items can be damaged by chemicals, heat or pressure
UV radiation
- changes to DNA structure (thyamine dimers) = mutations
- bacteria can repair unless high doses of UV used
- Reduced microbes to 99% (disinfectant)
- very effective against actively reproducing cells but not endospores because of mutations
Disadvantages of UV radiation
stopped by solids: used on air, some liquids & surfaces
- also damages human tissue
Ionizing radiation
x-rays and Gamma rays - very high energy wavelengths
- remove electrons: breaks DNA and cell membrane
- Used in food preparation and in some hospital settings
- can penetrate most solids - fabric, plastic, food
- Gram - bacteria very susceptible
Disadvantages of ionizing radiation
- not effective on endospores
- damages human tissue
filtration
- filters with pores from 0.02 - 8 micrometers
- will filter our bacteria and some viruses
- good for heat sensitive fluids (beer, wine)
- Air filtration used in sterile environments (OR)
Disadvantage of filtration
- does not capture small viruses or toxins
- does not destroy microbes
