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Destruction of all living microbes, spores, and viruses


Lowers germ levels (washing utensils)


Kill by oxidation (proteins, breaking of H20 bound)


Direct flame to kill microbes

Dry heat (The hot-air oven)

Long exposure time required for heat penetration. 160-180°C for 2 hours. Works by oxidizing proteins, dehydration. Used for corrosive metals, powders, oils, some reusable glassware.

Moist heat (more effective - More rapid penetration than dry heat)

Includes: boiling, autoclave, pasteurization. Conduction (heat is continuous without air) vs. Convection (heating involving air)


Moist heat and pressure. Uses 121°C, 15 psi 15-30 minutes. coagulation of proteins.


Cold loving; Temperature Range: 0-20; Optimim: 10-15; Found in refrigerator, freezer, cold water, snow, ice, etc.; not found in the human body


20-40 C; human pathogens; most grow best at 37`C (human body temp)


Heat-loving, 40 - 80 degrees.


Organuisms that survive at high temperatures but do NOT multiply. (e.g. Endospore)

UV Light

265 nm = most destructive to living cells. Effect: Pyrimidine dimers (DNA changes). Must be direct exposure to penetrate.

What range of ultraviolet is most harmful to microorganisms?

200-280 nm

What other types of radiation could be used to control microorganisms?

Gamma & X radiation

How can drying or dessication of bacteria be applied to health care? What items should be kept dry?

Dessication (drying) is the removal of moisture from the body of an organism. Many bacteria are very sensitive to water loss and can be killed simply by removal of water. For example, Treponema pallidum, the agent of syphillis, is so intolerant to water loss that it will die within twenty seconds on the surface of a dry fomite. The physical preservation of foodstuffs by drying has been practiced by humans for thousands of years and in most cases does reduce the number of potentially pathogenic microbes.

What is lyophilization? Give applications of this process.

Lyophilization is a way of drying something that minimizes damage to its internal structure. (Freeze Drying) Lyophilization is used by botanists to preserve flower samples indefinitely

Are most microorganisms destroyed by cold temperatures?

No, cold temperature slows down bacterial growth.

What effect would alternate freezing and thawing have on bacteria?

Repeated freezing and thawing may cause cell damage to the meat, releasing nutrients, making them more available to bacteria. Repeated thawing increases the time that the meat is at a temperature that bacteria can grow.

What are the conditions for effective sterilization by incineration?

When there's no regard to host or the microorganism, it is total destruction.

What kinds of organisms are hardest to destroy by heat? Name four.

Endospore forming. Bacillis subtilis, Clostridium tetanus, Clostridium botulism, Clostridium perfrigins

Name two organisms that are very heat-labile?

Endospore: Bacillis & Clostridium

What is the thermal death point?

The lowest temperature needed to sterilize a pure culture of bacteria in 10 minutes.

What is the thermal death time?

The time require to sterilize a culture in a given temperature.

What is "fractional sterilization"?

sterilized by exposure to free flowing steam at 100oC for 30 minutes on each of 3 successive days, with incubation periods between the steaming; a fraction was accomplished on each day. It was also called tydallization after its developer, John Tyndall.

What is the relationship of time to temperature in heat sterilization?Explain.

the higher the temperature, the less time needed for sterilization. Inverse proportional relationship.

Why does sterilization by hot air take so long?

Because it needs to break the water bonds

What type of items can best be sterilized in a hot air oven?

Glassware (flasks, pipettes, syringes), metals, powders, oils, petroleum jelly


100 C must adjust duration & substrate. Substrate can increase temperature above 100. Increase length of time of boiling can increase likely hood of sterilization.

Zone of inhibition

clear zone around disc paper, area that has no growth. Size=expresses chemical effectiveness.

Filter paper disc method

disc of altered paper impregnated with chemical agents.


used on living tissue. e.g. Hydrogen peroxide, Alcohol


used on non-living surfaces. e.g. Vesphere, Clorox, Zephorine Cl.

Antimicrobial Susceptibility Test

Means bacteria will be slow down or killed by an antibiotic. Kirby-Bauer Method: filter paper disc impregnated with different antibiotics.

Kirby-Bauer Method

Filter paper disc impregnated with different antibiotics.

Mueller-Hinton Agar

Specific media, no nutritional value, won't inhibit or hinder growth.

Streak lawn

Streak and cover the plate in both directions.

Acridime Dyes

At low concentration kills gram (-) bacteria. e.g. Proflavin, Acriflavin

Triphenylmethane Dyes

Low concentration inhibits gram (+). High concentration will inhibit both gram (+) and gram (-). e.g. Malachile green, Bismarck brown, Crystal Violet.

Indirect contacts

Transmission by FORMITES.


Hospital acquired infections


contaminating organism easily removed w/soap & water usually in 7-8 mins.

Susceptible, Resistant, Intermediate

Susceptible=Bacteria is killed by antibiotic (good for use), Resistant=Bacteria is not affected by antibiotic (don't use on patient), Intermediate=some bacteria is affected and others may not by the antibiotic (don't use on patient)

How does Gram reaction of organisms determine the type of antibiotic to be used?

Because some antibiotic will only work on Gram (-) or (+) while others (broad spectrum) may work on both.

What is the difference between an antibiotic and chemotherapeutic agent?

Antibiotic is for bacterial diseases. Chemotherapeutic agent is for infectious diseases (may target more than just bacteria)

What is meant by "drug resistant" microorganisms and how did they arise?

Example of bacteria, where some are resistant to penicillin. this came about due to over use of the antibiotic to allow for bacteria to develop the resistance factor which is spread through their subsequent populations.

What is a Broad spectrum antibiotic?

Broad spectrum drugs affect many bacterial groups, work on gram +/-. Ex. Tetracycline

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