Sterilization and Disinfection Flashcards
What is antisepsis?
Prevents sepsis (infection) by killing infectious microorganisms
What is sterilization?
Kills all forms of microbial life
It is desirable but not always feasible
What is disinfection?
Same as antisepsis (preventing sepsis by killing microorganisms) except applied to inanimate objects
What is santization?
Reducing the number of microorganisms
What are sterilizers?
They are used to eliminate all forms of microbial life including fungi, viruses, bacteria, and their spores
What are antiseptics and germicides and how are they different from disinfectants?
Antiseptics and germicides are used on humans/animals to inhibit growth of microorganisms and they are regulated by the FDA. Disinfectants are used on hard inanimate surfaces
Is destruction of microorganisms equivalent to sterilization? Why?
No, killing microorganisms in an intravenous solution could release pyrogenic compounds causing toxic shock
Solutions should be sterilized so that bacteria never have the chance to grow
Death rates of bacteria during sterilization follow what trend? How long does it take phenol to kill bacteria down to 1% of the population?
Exponential
~30 minutes
Death rate of spores follow what trend? How long does it take phenol to kill spores down to 1% of the population? What is the rate constant compared to death of bacteria?
Exponential but much slower
~6 hours
Rate constant is 1000 fold less
Killing spores is a major problem
During sterilization, is there an absolute time when 0 organisms remain?
No
Kinetics vary with ______ populations
low
Kinetics are affected by composition of what?
Suspending medium
For example, aggregates of bacteria can survive longer
Bacterial spores are relatively __________ to killing by all means of sterilization
resistant
Endospores are formed in response to what?
Nutrient depletion
Spores contain everything necessary to
regenerate vegetative cells
What is the bacterial spore basis to resistance?
Extremely low water content (and high Ca2+) due to dipicolinic acid
What does dipicolinic acid do?
Chelates Ca2+
Stabilizes DNA by intercalation
What specifically initiates sporulation?
GTP deficiency
An unfavorable environment leads to decreased amino acids which leads to increased ppGpp, inhibiting GTP synthesis
Sigma factors are initiating proteins associated with what?
RNA polymerase
Sigma 29 is a sporulation specific factor of what bacteria?
B. subtilis
What is sigma 55?
Its for vegetative growth
What are the three stages of regeneration of vegetative cells?
Activation
Germination
Outgrowth
For the regeneration of vegetative cells, activation generally occurs by
heat or chemicals
one possibility is the inactivation of a critical protein
Describe the germination phase of regeneration of vegetative cells
Irreversible
Requires water
Accompanied by loss of resistance
Doesn’t require nucleic acid or protein synthesis
During the outgrowth stage of regeneration of vegetative cells, there is active what?
Biosynthesis
There are four medically important species of anaerobic spore-forming bacteria are what?
C. tetani - tetanus
C. botulinum - botulism
C. perfringens - gas gangrene
C. difficile - diarrhea
C. difficile exists as vegetative cells or spores?
Both
Which form of C. difficile produces the toxin?
Vegetative form
What is the main mode of transmission for C. difficile?
Spores
Survive on dry surfaces for several months
Resistant to heat, antibiotics, acid, and alcohol hand disinfectants
What happens after ingestion of C. difficile?
Spores germinate into vegetative cells in the colon and produce toxin
Are alcohol disinfectants effective against C. difficile? What can you do?
No, just don’t come into contact with it (gloves, gowns, etc)
What are 3 chemical agents that damage the cell membrane?
Surface active compounds
Phenolic compounds
Alcohols
What are surface active compounds?
Detergents Cationic agents (Zephiran) Anionic agents (SDS) Nonionic agents (Tween 80)
Are nonionic agents effective?
No, they can even serve as nutrients for bacterial growth
Two examples of alkyl and chloro phenols (which are less potent than pure phenol)?
Lysol
Triclosan
Example of a halogenated diphenyl?
hexachlorophene (soap withdrawn from OTC sales because falsely accused of being carcinogenic)
What is the optimal ethanol concentration to kill bacteria? Why not 100%?
50-70%, any higher than that the bacteria become dehydrated and they are harder to kill
Is isopropanol more or less effective than ethanol?
More, but its more toxic as well
Does alcohol kill spores?
Nope
What are the organic acids benzoic and proprionic used for?
They denature bacterial proteins and are used in preservatives and pharmaceuticals
Alkyl esters of organic acids (benzoic and proprionic) act like alkyl-substituted phenols. Why aren’t they toxic once ingested?
They are rapidly hydrolyzed to p-hydroxy-benzoate
What are four things that modify proteins and nucleic acids of bacteria directly?
Heavy metals
Oxidizing agents
Dyes
Alkylating agents
How do heavy metals act on bacteria? How can they be reversed?
They interact with sulfhydryl groups (many if not most proteins have these)
They are effective at low concentrations (1 ppm)
Reversed by sulfhydryl compounds
What are silver nitrate and silver sulfadiazine used for?
Silver nitrate is used in the eyes of newborns to prevent gonococcal infections
Silver sulfadiazine is used to prevent skin infections in burn patients
Is iodine an oxidizing agent? How does it work?
Yes
It combines with proteins and iodinates tyrosine residues
In what form is iodine used? What makes it less painful?
KI is used but it is very painful and destructive
Combining it with a detergent (iodophores-betadyne)
What is iodine effective against?
Spores
Do hydrogen peroxide and organic peroxides work better on anaerobes or aerobes? Why?
Anaerobes because they lack catalase
Cl and hypochlorite oxidizing agents yield what? What are they used on?
Hypochlorous acid (HOCl) Inanimate objects
What are the names of two types of dyes?
Triphenylmethanes
Acridines
What are triphenylmethanes?
Topical skin treatment dyes - used on burn patients
Crystal violet, brilliant green, malachite green
What are acridines?
Used for wound antisepsis
Mutagenic - insert into DNA
Carcinogenic
Proflavine, acriflavine
What are alkylating agents, how do they work?
Active against spores at level equivalent to those necessary to kill vegetative cells
Used often, effective
They work by interacting with reactive species, killing enzymes
Formaldehyde, glutaraldehyde, ethylene oxide
What does formaldehyde, an alkylating agent, react with?
CO2-, SH, OH
What are the two ways that formaldehyde can be used, and what specific use does it have?
As an aqueous solution it is formalin (37% soln)
0.2-0.4% is used to inactivate virus to make vaccines
Also used as a gas for decontamination
It is carcinogenic
Glutaraldehyde: what does it react with, what is it used for?
Reacts with SH and NH groups
Cold sterilant for surgical items (or whatever) that won’t hold up in heat
10x as effective as formaldehyde
Ethylene oxide: what is it used for?
It is extremely reactive, biohazard
Used by companies that make hospital equipment
Sterilization with heat is dependent on which factors?
Time, temperature, pressure, water
Is sterilization with heat slower or faster without water?
Slower without water
What is tyndallization?
Fractional sterilization method
Heat to 80-100 degrees C for 30 mins for 3 days
Spores activated each cycle then killed
What is pasteurization?
Reduces the number of microorganisms and kills most pathogens
Heat to 62 degrees C for 30 minutes
Should freezing/thawing be used for sterilization?
No
What can damage skin and eyes but has low penetrating power?
UV radiation
What produces pyrimidine dimers in DNA? What are they repaired by?
UV radiation
Photoreactivation or SOS repair
What is UV radiation used for?
Sanitizing rooms and tissue culture hoods
What is ionizing radiation used for?
Sterilization of surgical supplies and food, kills spores with the direct effect
What is the direct effect of ionizing radiation?
Energy directly damages macromolecules and kills spores
What is the indirect effect of ionizing radiation?
Ionization of H2O
Doesn’t kill spores
What pore size would you use to filter bacteria out of liquids?
0.22 microns
