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35 Cards in this Set
- Front
- Back
What factors effect the killing of organisms? |
1. # of organisms present |
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Killing of Organisms
# of organisms present |
it is harder to kill a larger population of cells
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Killing of Organisms
# of molecules (bullets of chemical agents) |
a more concentrated killing chemical agent may be more effective
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Killing of Organisms
time |
more exposure time, more death.
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Killing of Organisms
temperature |
increased temperature results in increased killing rate. The molecules are moving faster. |
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Killing of Organisms
pH |
altered pH can alter the potency. Depends upon the specific killing agent.
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Killing of Organisms
Media/Environment |
the more organic material present, the less susceptible to killing. Organic material can combine the chemical causing inactivation. Organic material can cause the chemical causing inactivation. Organic material can cause the chemical agent to precipitate out of solution. Organic material can coat the microorganism and protect it.
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Killing of Organisms
Type of Organism |
There are differences between bacteria, fungi and other infective agents. It is harder to destroy Gram negative bacteria then Gram positives. Bacterial spores are hardier and more resistant than fungal spores.
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Killing of Organisms
Physiologic State and/or Age of Organisms |
Younger bacterial cells reproduce more and are easier to kill than older cells. Chemicals have a greater chance of reacting with cells actively engaged in metabolic (growth) activities.
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What are examples of Physical Agents?
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1. Dry Heat
2. Moist Heat 3. Cold Temperatures 4. Lyophilization 5. Pasteurization 6. UV radiation 7. X-rays and gamma rays 8. Cathode rays 9. Filtration 10. Osmotic Pressure 11. Sonic Vibration (cavitation) |
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Physical Agents
Dry Heat |
conventional ovens set at 300 to 320 degrees F. for a period of 2 hours can be used for sterilizing pipettes with cotton for example. Open flames can be used to incinerate organism on inoculation loops.
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Physical Agents
Moist Heat |
a. Boiling water - will kill vegetative bacterial cells and eukaryotic spores (fungal). Will destroy most viruses. High altitude boiling occurs at a lower temperature and is less effective. Bottom line, boiling does not sterilize even with extended periods of boiling (ex. 30 min). Can be better than nothing. |
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Physical Agents
Cold Temperatures |
does not kill many bacteria. It is bacteriostatic . Used to preserve bacteria and viruses.
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Physical Agents
Lyophilization |
(freeze-drying or cryodessication)
a method of preservation |
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Physical Agents
Pasteurization |
63 degrees C for 30 min- kills human pathogens and serves to increase shelf life of a product by destroying many of the spoilage bacteria. Does not kill spore formers or destroy spores. Can use HTST (High temperature, short time) method commercially. Milk is heated at 71 degrees C. for 15 sec. Increase temperature and decrease the time for more fat content. (82.2 degrees C. for 1 sec. for cream). Beer, wine and fruit juices can also be pasteurized. Generally, pasteurization times are dependent upon the materials, potential pathogens and contaminants present.
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Physical Agents
UV radiation |
creates thymine dimers. Most lethal at 260-270 nm. Does not penetrate well. UV intensity is inversely proportional to the square of the distance from its target. Used mostly for aerial contaminants. Effectively used in areas where cultures are transferred, restaurants, operating rooms and meat storage areas. A visible light repair mechanism and a two step dark repair mechanism can reverse the damage.
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Physical Agents
X-rays and gamma rays |
hyperactive ions that ultimately cause protein, DNA and other damage. Destructive peroxide and super oxide formation occurs. Ionizing radiation is used to sterilize prepackaged dog food as well as increasing the shelf life of fruits and cold vegetables.
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Physical Agents
Cathode rays |
consist of a beam of electrons. Used for research purposes.
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Physical Agents
Filtration |
use filter grids that range from 0.2 to 0.45 micrometers for filtering out bacteria. Commonly used to sterilize thermo labile fluids such as human and animal serum and plasma. This is a slow and costly method. The filters oftentimes clog too easily. Urea in urea agar is sterilized using filtration. |
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Physical Agents
Osmotic pressure |
use high concentrations of salt and sugar to create hyper osmotic environments and therefore osmotic imbalances. 10 to 15% salt concentrations will inhibit most bacteria and microorganisms. 50% sugar concentrations will inhibit most bacteria and microorganisms.
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Physical Agents
Sonic vibration (cavitation) |
differential pressures created by targeting one side of a bacterial cell will cause the cell to burst. Used in research. A method for obtaining cell free extracts.
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What are Desirable Qualities of Chemical Agents?
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1. Selective toxicity |
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Phenol coefficient test for affectivity
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Test organisms |
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What are examples of Chemical Agents?
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1. Acids and bases |
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Chemical Agents
Acids and bases |
cause hydrolysis and coagulation of proteins. So toxic that they are rarely used.
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Chemical Agents
Phenols |
disrupt membranes and denature proteins. Active against vegetative cells. Not generally effective against spores. Stable to heat and can survive temperature extremes. Used by Lister.
a. phenol b. hexachlorophene - 2 phenols with 6 chlorines. Good for skin antisepsis. c. hexylresorcinol - phenol compound with sugar. Used in some soap. d. cresols (creosote is a derivative) - phenol compound with additional methyl groups. Good in presence of organic matter, but toxic to the skin. Used as a wood preservative against fungi. |
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Chemical Agents
Alcohols |
the longer its carbon chain, the better its killing effect.
a. one carbon-methyl alcohol b. two carbons-ethyl alcohol c. three carbons-propyl alcohol d. four carbons-butyl alcohol Longer chains enter the cell more readily, shorter chained alcohols tend to get bound during entry. Alcohol denatures proteins in cell. Good for skin antisepsis. Optimally active at 70% concentrations. At higher concentrations the improved dehydration effect actually inhibits the alcohol during cell entry. Alcohols are good against Gram positive and Gram negative bacteria, fungal spores and enveloped viruses. They are not effective against bacterial spores and non-enveloped viruses. |
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Chemical Agents
Halogens |
work by combining with proteins and rendering them ineffective. Active against spores, viruses and fungi. Chlorine and Iodine compounds predominantly |
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Chemical Agents
Heavy metals |
combine with proteins |
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Chemical Agents
Dyes or biological stains |
combine with proteins
a. crystal violet (gentian violet) - inhibits gram positive bacteria in cultures. Also used as an antifungal agent. b. potassium permanganate- acts as an oxidizer. Used against fungal infections of the hands and feet. Also used in water disinfection. |
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Chemical Agents
Quaternary ammonium compounds |
disrupts cell membranes. Also denatures proteins. Chemically central nitrogen is attached to four side chains. This nitrogen compound is positively charged. This compound is linked to a chloride anion. Is used in disinfection of utensils in dairies and restaurants. Quats have no effect on spores. Benzalkonium chloride is an example of a quat.
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Chemical Agents
Glutaraldehyde |
(“cidex”) |
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Chemical Agents
Ozone and Hydrogen peroxide |
(oxidizing agents) |
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Chemical Agents
Formaldehyde |
acts as an alkylating agent. Used in vaccine preparation and in specimen preservation. Formaldehyde will inactivate viral particles for use in vaccines. Chemically formaldehyde is built from one aldehyde group.
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Chemical Agents
Ethylene oxide |
an alkylating agent that is a gaseous chemosterilant commonly used in hospitals. A ringed structure built from two carbons and oxygen that is a highly instable chemical. It is used in the sterilization of heat-labile materials (plastic petri dishes used in lab.). Effective against vegetative bacteria, spores and viruses.
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