Ch.7 Control of Microbial Growth

Decimal reduction time is the time in minutes in which __________ of the population at a given temperature will be killed. a)90% b)75% c)100% d)10%

a)90%

Which of the following are NOT major targets for action of antimicrobials? a)Flagella b)Enzymes c)Cell membranes d)Nucleic acids e)Proteins

a)Flagella

Which one of the following physical methods of microbial control is bactericidal? a)Incineration b)Refrigeration c)Desiccation d)Deep-freezing

a)Incineration

Which of the following types of radiation is the LEAST effective control method against microorganisms? a)Microwaves b)UV light c)X rays d)Gamma rays

a)Microwaves

You are preparing a medium for growing fastidious bacteria and must add several heat-labile solutions of growth factors. Which of the following is an appropriate strategy for preparing and sterilizing this medium? a)Prepare and autoclave the medium before adding the growth factors. b)Prepare the medium, add the growth factors, and autoclave. c)Use dry heat to sterilize the medium. d)Pasteurize the medium. e)Use UV radiation to sterilize this medium.

a)Prepare and autoclave the medium before adding the growth factors.

Which of the following is LEAST likely to be damaged by exposure to gamma radiation? a)Prions b)Bacteria c)Fungi d)Protozoa e)Viruses

a)Prions

__________ bacteria may survive pasteurization. a)Thermoduric b)Mesophiles c)Psychrophile d)Psychotroph

a)Thermoduric explanation: Thermoduric bacteria may survive pasteurization. Pasteur used mild heating, which was sufficient to kill the organisms that caused spoilage in beer and wine without seriously damaging the taste of the product. The same principle was later applied to milk to produce what we now call pasteurized milk. The intent of pasteurization of milk was to eliminate pathogenic microbes. It also lowers microbial numbers, which prolongs milk's good quality under refrigeration. Many relatively heat-resistant, thermoduric, and endospore-forming bacteria may survive pasteurization.

While waiting for your meal at a restaurant, you read the information on the creamer containers at your table and notice that they do not need to be refrigerated. You are surprised, because dairy products typically must be kept cold to prevent spoilage. How were these products treated to eliminate microbial growth and prevent spoilage? a)Ultra-high-temperature (UHT) treatment b)Pasteurization c)Gamma irradiation d)Chemical preservatives

a)Ultra-high-temperature (UHT) treatment explanation: Milk can also be sterilized—something quite different from pasteurization—by ultra-high temperature (UHT) treatments. It can then be stored for several months without refrigeration. In the United States, UHT is used on the small containers of coffee creamers found in restaurants. During this process, the liquid milk (or juice) is sprayed through a nozzle into a pressurized chamber filled with high-temperature steam. 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°C for 4 seconds, the fluid is rapidly cooled in a vacuum chamber. The milk or juice is then packaged in a pre-sterilized, airtight container.

All of the following methods are used for food preservation EXCEPT __________ a)direct flaming b)deep freezing c)dessication d)osmotic pressure e)commercial canning

a)direct flaming

Pasteurization was first used by Pasteur to control spoilage of __________. a)wine b)canned foods c)milk d)cheese e)yogurt

a)wine

You contaminate the kitchen counters with Salmonella enterica in chicken blood and expose it to a variety of treatments to study the survival of the bacteria on kitchen surfaces. The following DRT values were obtained: 2.0 minutes at 52°C; 3.7 minutes at pH 2.6; 13.3 minutes with 10 mM hydrogen peroxide; and > 35 days without treatment. Which treatment is most effective against S. enterica? a)The most effective treatment cannot be determined from the given data. b)Heat (52ºC) c)10 mM hydrogen peroxide d)These are equivalent treatments. e)Acid (pH 2.6)

b)Heat (52ºC)

For control of microbial growth on a surface, which of these conditions is LEAST likely to interfere with the effectiveness of an antiseptic or disinfectant? a)Presence of biofilms b)Warm environmental conditions c)Presence of organic matter d)High numbers of microbes

b)Warm environmental conditions

A chemical that reduces spoilage in fruit by destroying fungi but does NOT appear to affect other microbes would be called a __________. a) sterilant b)fungicidal agent c)fungistatic agent d)bactericidal agent

b)fungicidal agent

An antiseptic is used to remove microbes from __________. a)foods before canning them b)skin before an injection c)food preparation areas d)toilet surfaces e)restaurant glassware

b)skin before an injection

You discover a compound that you suspect reduces spoilage in fruit. You treat apples with your compound and inoculate them with Botrytis, a common spoilage fungus. After 7 days, the dry weight of fungi is 5 mg on the treated apples and 10 mg on the untreated apples. You conclude from these results that __________. a)the compound is toxic to humans b)the compound is fungistatic c)apple spoilage is caused by fungi d)the compound kills fungi e)the fungus probably will have no effect on the apples

b)the compound is fungistatic

The DRT for a particular bacterial species at 60°C is 30 minutes. How long would it take at this temperature to remove 99.9% of this bacterial population? a)10 minutes b)30 minutes c)90 minutes d)120 minutes e)60 minutes

c)90 minutes

Which of the following treatments achieves sterilization? a)Pasteurization b)Freezing c)Autoclaving d)Bringing water to a boil

c)Autoclaving

Operating rooms may receive ventilation from air that has passed through __________ filters to remove microorganisms. a) air b)UV c)HEPA d)dust

c)HEPA

Which of the following correctly describes antisepsis? a)Destruction of vegetative microorganisms on inanimate surfaces b)Destruction of all organisms on any surface c)Removal of vegetative microorganisms from living tissue d)Reduction of microbial cells on eating or drinking utensils

c)Removal of vegetative microorganisms from living tissue

Sterilization is the __________. a)destruction of all forms of microbial life except endospores b)elimination of all gram-negative bacteria c)destruction of all microbial life d)reduction of microbial growth e)elimination of vegetative bacterial cells and fungal spores

c)destruction of all microbial life

Which of the following is true of an antimicrobial substance with a microbial death rate of 90% after 1 minute? a)After the first 2 minutes of application of the agent, 10% of the original microbial count survives. b)After 1 minute of application of the agent, 75% of the microbes would be killed. c)All of the microbes would be killed instantly upon application of the agent. d)After the first minute of application of the agent, 10% of the original microbes are still left on the surface.

d)After the first minute of application of the agent, 10% of the original microbes are still left on the surface. explanation: Decimal reduction time (DRT, or D value) is the time, in minutes, in which 90% of a population of bacteria at a given temperature will be killed. Therefore, it would be correct to state that after the first minute of application of the agent, 10% of the original microbes are still left on the surface.

Which term refers to an agent that inhibits bacterial growth? a)Fungicidal b)Homeostatic c)Bactericidal d)Bacteriostatic e)Germicidal

d)Bacteriostatic

Which term refers to an agent that inhibits bacterial growth? a)Bactericidal b)Germicidal c)Fungicidal d)Bacteriostatic e)Homeostatic

d)Bacteriostatic explanation: A bacteriostatic agent inhibits bacterial growth. The suffix "-stat" or "-stasis," means to "stop" or to "steady," as in bacteriostasis. Once a bacteriostatic agent is removed, growth might resume.

Which of these conditions is likely to interfere with the effectiveness of an antiseptic or disinfectant? a)Absence of endospores b)Increased time of exposure c)Increased temperature d)Presence of biofilms

d)Presence of biofilms

Which of these is NOT a characteristic of the autoclave? a)The use of high temperatures b)The ability to sterilize solutions with endospores c)The use of high pressures d)The requirement for long (hours) exposure times e)The use of moist heat

d)The requirement for long (hours) exposure times explanation: Autoclaving is the preferred method of sterilization in health care environments, unless the material to be sterilized can be damaged by heat or moisture. The higher the pressure in the autoclave, the higher the temperature. It does not require as long of exposure times as other methods. Sterilization in an autoclave is most effective when the organisms either are contacted by the steam directly or are contained in a small volume of aqueous (primarily water) liquid. Under these conditions, steam at a pressure of about 15 psi (121°C) will kill all organisms (but prions) and their endospores in about 15 minutes.

Pasteurized milk in an unopened container spoils in the refrigerator. A sample reveals the presence of microorganisms. The most likely explanation is __________. a)the milk was pasteurized too long b)the pasteurization process was ineffective c)the microbes are pathogens d)pasteurization-resistant mutants developed after pasteurization e)the microbes that survived pasteurization were able to grow at 4ºC

e)the microbes that survived pasteurization were able to grow at 4ºC

Packages of milk and coffee creamers may be stored without refrigeration if they have been sterilized by __________. a)autoclaving b)high-temperature short-time (HTST) pasteurization c)treatment with phenol d)boiling e)ultra-high-temperature (UHT) treatment

e)ultra-high-temperature (UHT) treatment explanation: Milk can also be sterilized by ultra-high-temperature (UHT) treatments. It can then be stored for several months without refrigeration UHT-treated milk is widely sold in Europe; in the United States, UHT is sometimes used on the small containers of coffee creamers found in restaurants. 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°C for 4 seconds, the fluid is rapidly cooled in a vacuum chamber. The milk or juice is then packaged in a pre-sterilized, airtight container.