Lecture 7B

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Answer

Sterilization

kills all living orgaimsms on object, including endospores

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Disinfectants

do not kill all organisms and spores, used on inanimate objects

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Antiseptic

used on living tissue. Does not kill all organisms.

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Degerm

E.g. swabbing with alcohol. Mostly mechanical removal of microbes. Limited effectiveness.

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Sanitization

Lowers numbers of microbes. E.g. high temperature dish washing.

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Germicide

Kills microorganisms; may not be effective on all types.

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Bacteriostat

Stops microorganisms from growing.

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Disinfectants and Antiseptics

Inactivate enzymes (change the shape; like frying an egg) e.g. heat; ammonia

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Disinfectants and Antiseptics - Injure plasma membranes

Damage proteins or lipids e.g. alcohol

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Disinfectants and Antiseptics Damage DNA

ionizing radiation - gamma radiation ionizes water to form hydroxyl radicals. H2O ---> H+ and OH-. These radicals react with DNA and protein

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Disinfectants and Antiseptics non ionizing radiation -

UV light causes thymine dimers to form . Replication of DNA can be disrupted. Sometimes the repair mechanisms of cell can get rid of the dimers. Sometimes not

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Factors that Influence microbial death

Number of organisms (note that kill is expressed as log of # of cells)

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Microbial characteristics mycobacteria

e.g. M. tuberculosis, cell wall has large amt of lipid, so resistant to environment stress like drying. also resistant to many disinfectants

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Microbial characteristics endospores

e.g. Bacillus

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Microbial characteristics gram -/+

in general gram + easier to kill with H2O soluble disinfectants (gram+'s more resistant to drying and physical disruption because of thick peptidoglycan layer; Psudomonads (gr-) are very hard to kill and have been found in hospital disinfection solutions

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Microbial characteristics Organic matter

pH (easier to kill with heat if environment more acid)

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List 3 factors determining effectiveness of disinfection

Time, concentration of disinfectant, temperature

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Physical Methods of Disinfection- Heat (moist)

Moist (autoclave (fig. 9.7 and 9.8 121°C 15 min. Kill is more effective in presence of water. Kills endospores too. Organic material does not interfere) Autoclaves are tested using an endospore former (Baciluus stearoathermophilus)

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Physical Methods of Disinfection- Heat (Dry)

(flaming, 170°C 2 hrs.-- less efficient. Takes longer. Must be hotter.)

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Physical Methods of Disinfection- Pasteurization

Does not kill everything. 63°C 30 min. takes care of almost all pathogens, incuding M. tuberculosis

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Physical Methods of Disinfection- Cold

Remember the psychrophiles!, generally bacteriostatic

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Physical Methods of Disinfection- Filtration

(blank)

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Physical Methods of Disinfection- Drying

Not reliable, esp. if organic material around

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Physical Methods of Disinfection- Radiation

Interrupts the ability of DNA to accurately replicate

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Physical Methods of Disinfection- Chemical Methods phenols/biguanides

chlorhexidine surgical scrub injues plasma membranes ; phenols like listerine are most effective above 1% and denature enzymes.

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Physical Methods of Disinfection- Chemical Methods halogens

chlorine, iodine. Iodine interacts with the amino acid tyrosine

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Physical Methods of Disinfection- Chemical Methods alcohol

disrupts lipids denatures enzymes. 70-95% is most effective. Having a little water mixed in increases the effectiveness of the alcohol as a disinfectant. Alcohol-based agents for cleaning skin have been found as effective as good hand washing with soap.

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Physical Methods of Disinfection- Chemical Methods surface active agents

soaps and detergents are by themselves not all that effective against killing bacteria. Mostly they work by mechanically removing dirt and bacteria, and emulsifying oils --helping to lift bacteria off surfaces. The alkaline nature of soaps help kill some.

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Disinfection- Quats

quarternary ammonium compounds. e.g. benzelkonium chloride and Zepherin. These are more effective for gram negatives than gram positive and may not work for TB, or endospores. They are effective for fungi.

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Disinfection - aldehydes

Wavicide, Cidex. 2% glutaraldehyde sols. which can be quite effective. Used for soaking surgical equip.(endoscopes, etc.) which can't be autoclaved. Soak time can be critical. Often used for 15-20 mins. Might need 3+ hrs for efficacy

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Disinfection - peroxides

hydrogen peroxide. Although used on skin it is quickly broken down by enzymes in skin and other tissues. It is better used on surfaces.

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Types of Water used in Hospitals - distilled

Water can be distilled (heated and recondensed to remove chemical contaminants

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Types of Water used in Hospitals - deionized

run thru special filters to remove ions such as cholorine and sodium

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Types of Water used in Hospitals - Pyrogen Free

Pyrogens are a lipopolysaccharide in the outer membrane of gram - cell walls. When gram - cells are killed or die these pyrogens are released into the bloodstream causing blood clots, shock, death. Must be tested and proven pyrogen free Used for inject

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