Chapter 7 On Physical Methods Of Microbial Control

Front 1

What physical methods of microbial control did stone age humans most likely used to preserve their food?

Back 1

Drying (desiccation) and salting (osmotic pressure).

Front 2

What are some factors when selecting methods of microbial control?

Back 2

Heat may be a factor when selecting a microbial control because certain vitamins or antibiotics may be inactivated in a solution. Heat may also damage laboratory and hospital materials such as rubber and latex tubing.

Front 3

What are some economic considerations for selecting a microbial control agent?

Back 3

It may be cheaper to do a method one way than another such as using presteralized, disposable plasticware than to repeatedly wash and resterilize glassware.

Front 4

What is a thermal death point (TDP)?

Back 4

The lowest temperature at which all the microorganisms in a particular liquid suspension will be killed in 10 minutes.

Front 5

What is a thermal death time (TDT)?

Back 5

The minimal length of time for all bacteria in a particular liquid culture to be killed at a given temperature.

Front 6

What is a decimal reduction time (DRT or D value)?

Back 6

The time in minutes in which 90% of a population of bacteria at a given temperature will be killed.

Front 7

Explain the relation between moist heat sterilization and how it affects the proteins in a microorganism.

Back 7

Moist heat kills microorganisms primarily by coagulating proteins (denaturation), which is caused by breakage of hydrogen bonds that hold the proteins in their three-dimensional structure.

Front 8

Name one method of moist heat sterilization and what does moist heat sterilization kill a mircoorganism and how long does it usually take to kill a microorganism.

Back 8

Boiling is one method of moist heat sterilization and it kills vegetative forms of bacterial pathogens, almost all viruses, fungi and their spores in about 10 minutes.

Front 9

Is free-flowing (unpressurized) steam essentially the same temperature as boiling water?

Back 9

Yes.

Front 10

What kind of microorganism can be resistant to free-flowing steam and boiling water and how long can some of these microorganisms survive when boiled?

Back 10

Endospores and some viruses can be resistant to boiling. Some hepatitis viruses can resist boiling for up to 30 minutes and some bacterial endospores can survive more than 20 hours.

Front 11

Is boiling always a reliable sterilization procedure?

Back 11

No.

Front 12

Can brief boiling at high altitudes kill most pathogens?

Back 12

Yes.

Front 13

What does moist heat sterilization need to become a reliable sterilization?

Back 13

It needs a temperature above boiling water.

Front 14

What can make steam reach a higher temperature and what is the device that can achieve this?

Back 14

Steam can reach a higher temperature through pressure and it can be achieved through a device called an autoclave.

Front 15

What is the prefered method of sterilization?

Back 15

Autoclaving.

Front 16

What is one reason to not use an autoclave?

Back 16

A reason not to use an autoclave is because a material may be damaged by heat or moisture.

Front 17

What is the relation between pressure and temperature in an autoclave?

Back 17

The higher the pressure in an autoclave will make the temperature higher.

Front 18

What happens when free-flowing steam at a temperature of 100 degrees Celsius is placed under 15 psi?

Back 18

The temperature of the free-flowing steam rises to 121 degrees Celsius.

Front 19

What happens when free-flowing steam at a temperature of 100 degrees Celsius is placed under 20 psi?

Back 19

The temperature of the free-flowing steam rises to 126 degrees Celsius.

Front 20

When is sterilzation most effective in an autoclave?

Back 20

When an organism is either contacted by steam or contained in a small volume of aqueous (primarily water). Under these conditions, steam at a pressure of about 15 psi (121 degrees Celsius) will kill all organisms (but not prions) and their endospores in about 15 minutes.

Front 21

What kind of things can an autoclave sterilize?

Back 21

An autoclave can be used to sterlize culture media, instruments, dressings, intravenous equipment, applicators, solutions, syringes, transfusion equipment and numerous other items that can withstand high temperatures and pressure.

Front 22

What is a large industrial autoclave called?

Back 22

A retort.

Front 23

Are the principles of an autoclave the same as a household pressure cooker that is cooking a canned food?

Back 23

Yes.

Front 24

Does heat require more time to reach the center of a solid material than a liquid? If yes, why?

Back 24

Yes because solids do not develop the efficient heat-distributing convection currents that liquids do.

Front 25

Does heating a large container of liquid require more time than a small container of liquid to sterilize?

Back 25

Yes.

Front 26

Can you sterilize a solid with some areas blocked out to steam during a moist heat sterilization.?

Back 26

No. A solid requires the steam to actually contact the surface to sterilize it.

Front 27

What must you make sure when you sterilize glassware and bandages by moist heat sterilization?

Back 27

That the steam would be able to contact all surfaces.

Front 28

Should you use aluminum foil to wrap dry material when using moist heat sterilization? If not, why and what material can you use?

Back 28

No because aluminum foil is impervious to steam and paper should be used instead.

Front 29

When using moist heat sterilization, what must you be aware of when sterilizing a dry container and why?

Back 29

You must be aware of the trapping of air in the bottom of a dry container. Trapped air will not be replaced by steam because steam is lighter than air.

Front 30

What must you do to a container that can trap air when using moist heat sterilization and why?

Back 30

Place it in a tipped position so that steam will force out the air.

Front 31

Can products like mineral oil or petroleum jelly be penetrated by the moisture in moist heat sterilization? If not, can you use the same methods used to sterilize aquous solutions in moist heat sterilization?

Back 31

No and no.

Front 32

Are there commercially available methods that can indicate a heat treatment achieved sterilization?

Back 32

Yes. (Page 190 of Mircrobiology: An Introduction 10th Edition for examples)

Front 33

Can steam sterilize when air is not completely exhausted in an autoclave? What must you make sure you do not do when handling an autoclave?

Back 33

No and you must make sure you do not prematurely close an autoclave's ejctor valve.

Front 34

What must you do while using a pressure cooker and what happens if you do not do this step?

Back 34

You must let the steam flow vigorously at the valve in the lid for serveral minutes to carry out all the air before the pressure cooker is sealed and if not, the air will cause the container to not reach the temperature at a given pressure.

Front 35

What can occur from improper canning methods?

Back 35

Food poisoning from botulism.

Front 36

Who found a practical method of preventing the spoilage of beer and wine?

Back 36

Louis Pasteur.

Front 37

What did Pasteur do to a product that sufficiently kill an organism that caused particular spoilage problems without seriously damaging the taste of the product?

Back 37

Mild heating.

Front 38

What is mild heating applied to milk called?

Back 38

Pasteurized milk.

Front 39

What is the intent of the pasteurization of milk?

Back 39

To eliminate pathogenic microbes and lower microbial numbers to keep the quality of the milk good under refrigeration.

Front 40

What can survive pasteurization but unlikely to cause a disease or cause refrigerated milk to spoil?

Back 40

Thermoduric bacteria.

Front 41

Does ice cream, yogurt and beer have the same pasterization time and temperatures?

Back 41

No.

Front 42

Is heating less efficient in foods that are more viscous?

Back 42

Yes.

Front 43

Can fats in food have a protective effect on microorganisms.

Back 43

Yes.

Front 44

What does the dairy industry use to determine if a product has been pasturized?

Back 44

A phosphatase test.

Front 45

Explain the process of a phosphatase test used in a dairy product.

Back 45

A phosphatase is checked if it is activated or inactivated after pasteurization. If phosphatase is inactivated, then the product is successfully pasteurized.

Front 46

What is high-temperature short-time (HTST) pasteurization?

Back 46

Milk pasteurization of at least 72 degrees Celsius for 15 seconds usually through a heat exchanger.

Front 47

What does high-temperature short-time (HTST) pasteurization do?

Back 47

Lower total bacterial counts so the milk keeps well under refrigeration.

Front 48

How can milk be sterilized?

Back 48

Through ultra-high-temperature (UHT) treatments.

Front 49

What can ultra-high-temperature (UHT) treaments do?

Back 49

Be sterilized without refrigeration for several months.

Front 50

Where is ultra-high-temperature (UHT) treated milk usually sold at?

Back 50

Ultra-high-temperature (UHT) treated milk is usually sold in Europe and less developed parts of the world where refrigeration facilities are not always available.

Front 51

What does the United States sometimes use ultra-high-temperature (UHT) for and where can you find the product of the ultra-high-temperature (UHT) treatment.

Back 51

Small containers of coffee creamers and usually found in restaurants.

Front 52

How does milk usually get a cooked taste using ultra-high-temperature (UHT) treatment?

Back 52

When the milk touches a surface hotter than the milk itself.

Front 53

What are the steps when milk (or juice) avoids getting a cooked taste using ultra-high-temperature (UHT) treatment.

Back 53

The milk (or juice) is sprayed through a nozzle into a chamber filled with high-temperature steam under pressure. A small volume of fluid sprayed into an atmosphere of high-temperature steam exposes a relatively large surface area on the fluid droplets to heating by the steam; sterilizing temperatures are reached almost instantaneously. After reaching a temperature of 140 degrees Celsius for 4 seconds, the fluid is rapidly cooled in a vacuum chamber. The milk or juice is then packaged in a presterilized, airtight container.

Front 54

What is an equivalent treatment and can you give an example and do both treatments yield the same result?

Back 54

When the temperature is increased, much less time is needed to kill the same number of microbes. For example, the destruction of highly resistant endospores might take 70 minutes at 115 degrees Celsius, whereas only 7 minutes might be needed at 125 degrees Celsius. Both treatments yield the same result.

Front 55

How does dry heat sterilization kill?

Back 55

By oxidation effects.

Front 56

Give an example of dry heat sterilization using paper.

Back 56

The paper is put into an oven and it is slowly charring, even when the temperature remains below the ignition point of the paper.

Front 57

What is the simplest method of dry heat sterilization?

Back 57

Direct flaming.

Front 58

What is the usual procedure of sterilizing an inoculating loop and how do you effectively sterilize it?

Back 58

The usual procedure of sterilizing an inoculating loop is direct flaming and you effectively sterilize it by heating the wire to a red glow.

Front 59

What is an effective way to sterilize and dispose contaminated paper cups, bags and dressings?

Back 59

Incineration.

Front 60

Is hot-air sterilization another form of dry heat sterilization?

Back 60

Yes.

Front 61

How is hot-air sterilization done?

Back 61

By placing items in an oven usually around 170 degrees Celsius for about 2 hours to ensure sterilization.

Front 62

Why does it usually take a longer period of time and a higher temperature when using moist heat sterilization in water?

Back 62

Because heat in water is more readily transferred to a cool body than is the heat in the air.

Front 63

What is filtration and how is it done?

Back 63

Filtration is the passage of a liquid or gas through a screen like material with pores small enough to retain microorganisms. A vacuum is created in the receiving flash; air pressure then forces the liquid through the filter.

Front 64

What is filtration used for?

Back 64

sterilizing heat-sensitive materials such as some culture media, enzymes, vaccines and antibiotic solutions.

Front 65

What do burn patients receive usually in operating theaters and rooms.

Back 65

Filtered air.

Front 66

What do High-efficiency particulate air (HEPA) filters remove?

Back 66

Almost all microorganism larger than 0.3 micrometers in diameter.

Front 67

How was unglazed porcelain used to filter liquids in the early days of biology and how does it absorb bacteria. What were the unseen pathogens that passed through the filters called?

Back 67

They were shaped to like a hollow candle and the long indirect passageways through the walls of the filter absorbed the bacteria. The unseen pathogens were called filterable viruses.