Chapter 9: Controlling Microbial Growth in the Environment
It has been determined that the temperature in an autoclave should reach _ for sterilization.
121 degrees Celsius The temperature is set at 121 degrees Celsius and 15 psi for 15 minutes to sterilize small volumes.
Which of the following is an example of sanitation? A pubic toilet is treated with disinfectants. A surgeon washes her hands before surgery. A nurse prepares an injection site with an alcohol swab. An autoclave is used to prepare nutrient agar. Heat is used to kill potential pathogens in apple juice.
A public toilet is treated with disinfectants.
Which biosafety level requires that laboratory air be HEPA-filtered but is insufficient for the safe study Ebola?
BSL-3
Why is autoclaving rather than boiling water used for sterilization?
Boiling water does not kill everything, including bacterial endospores and some protozoan cysts. Boiling watere reaches a maximum temperature of 100 degrees Celsius, compared with autoclaving where the temperature reaches at least 121 degrees Celsius. Boiling water is not hot enough to kill endospores or cysts in a reasonable amount of time.
Why do containers of liquid placed in the autoclave need to remain at least slightly open?
If they remain closed, they may implode. The extreme temperature and pressure changes within the autoclave may cause closed containers to implode.
What role does pressure play in an autoclave?
Pressure is applied to boiling water to prevent heat from escaping as steam. Adding pressure to boiling water leads to higher water temperatures.
Which of the following statements is TRUE of disinfectants? They are only effective for short periods of time (seconds to minutes). They are used for sterilization. They are effective in destroying endospores. They are used on inanimate surfaces. They are used on living tissue.
They are used on inanimate surfaces.
How do scientists ensure that autoclaved materials were actually sterilized?
They may place a sterility indicator with a special dye to detect the growth of endospores. Some sterility indicators have dyes that change color in the presence of living bacteria, indicating that the correct sterilizing temperature and time have not been reached.
What was the MOST likely source of the family's botulism food poisoning? The family consumed botulism toxin in the: chicken canned tomatoes green beans spinach salad
green beans C. botulinum is a soil microbe that could be found on green beans. If the canned beans were not prepared and canned properly, then the organism would be able to survive. It is less likely that C. botulinum could survive in canned tomatoes because tomatoes are very acidic.
Which of the following describes flash pasteurization? heating at 63 degrees Celsius for 30 minutes heating at 134 degrees Celsius for one second passing liquid through steam at 140 degrees Celsius heating at 72 degrees Celsius for 15 minutes heating at 72 degrees Celsius for 15 seconds
heating at 72 degrees Celsius for 15 seconds
Silvadene, a topical treatment for burns, contains 1% silver. What category of chemical control agent is in Silvadene?
heavy metals
Compared to moist heat methods, dry heat needs which of the following in order to sterilize effectively? lower temperature & shorter time higher temperature & shorter time higher temperature & increased time lower temperature & increased time
higher temperature and increased time
The lowest temperature that kills all cells in a broth in 10 minutes is known as the (microbial/thermal) death point.
thermal
What is the purpose of an autoclave?
to sterilize equipment and media
The phenolic _ present in many consumer products labeled "antibacterial."
triclosan
Milk that can be stored for months at room temperature has been treated by which of the following methods? batch pasteurization ultrahigh-temperature pasteurization ultrahigh-temperature sterilization flash pasteurization
ultrahigh-temperature sterilization
Which of the following is NOT an example of ionizing radiation? gamma rays electron beams ultraviolet light X rays
ultraviolet light
Which of the following is bacteriostatic? flash pasteurization autoclaving filtration freezing below 0 degrees Celsius heating in an oven at 171 degrees Celsius for an hour
freezing below 0 degrees Celsius
Which of the following is used for microbial control in fresh fruits and vegetables? electron beams X-rays microwaves gamma rays ultraviolet light
gamma rays
Why are endospores sometimes used in sterility indicators?
They are the hardest life form to kill.
A stationary broth culture contains 10 billion (10^10) cells. The microbial death rate during autoclaving of this spent culture is 1.5 minutes. How long must it be autoclaved to be considered sterile?
16.5 minutes
A broth containing one million bacterial cells is treated with an antimicrobial agent that kills 90% of the cells in 1 minute. What is the minimum amount of time it will take before all the cells in the broth are dead?
7 minutes
Which of the following best explains why the pressure cooker is so important in the canning process?
A pressure cooker utilizes steam to create a higher-pressure environment that allows the food to cook at higher temperatures than normal. The higher temperatures kill most contaminating microbes and endospores and therefore effectively sterilize the food. Pressure cookers rely on the relationship between pressures and temperature. As you increase pressure, you increase temperature at which liquids boil. The increase in pressure in a pressure cooker or an autoclave is a result of the production of steam within the chamber. Complete sealing of the chamber is essential for proper functioning of either piece of equipment. This increase in temperature and pressure allows for sterilization of many solids and small volumes of liquids within a very short period of time. When working properly, an autoclave or a pressure cooker reaches temperatures as high as 121 degrees C at 15 psi, which is hot enough to kill all organisms (except prions) and their endospores in about 15 minutes. This is an extremely useful sterilization technique for items that are not destroyed by high heat or moisture.
Glutaraldehyde acts on microbes by
forming chemical cross links in DNA and proteins
The decimal reduction time is the time required to kill all the microbes in a given sample.
False.
The pH conditions under which chemical disinfectant is used do not alter its efficacy.
False.
Use of moist heat can control microbial growth in many circumstances, but heat-sensitive items and those susceptible to moisture cannot be sterilized in this manner. Which of the following correctly describes a method of physical control used to control microbial growth on or in such items?
Filtration is the passage of liquid or gas through a screenlike material with pores small enough to retain microorganisms. A vacuum is typically used to force the liquid through the mesh, and then the sterile liquid or gas is collected in a sterile container on the other side. Nonionizing radiation, such as UV light, has a wavelength longer than that of ionizing radiation. The wavelengths of UV light are absorbed by cellular DNA in organisms directly exposed to the light. Desiccation is a process that removes water from microorganisms, leaving them unable to grow or reproduce, but still viable. Osmotic pressure is a process that uses high concentrations of salts and sugars to preserve food.
Which of the following is an example of microbial control? Sue washes off the vegetables before serving them in a meal. Mary warms food up in a microwave before putting it on the table. Sue uses bleach to clean the kitchen counters. Mary places leftover in the refrigerator after the meal.
Sue washes off the vegetables before serving them in a meal. Sue uses bleach to clean the kitchen counters. Mary places leftovers in the refrigerator after the meal.
Sodium nitrate and sodium nitrite are added to many meat products, such as ham, bacon, hot dogs, and sausage. These additives help to prevent the growth of Clostridium botulinum by inhibiting certain iron-containing enzymes of the organism. This is an example of chemical food preservation. Which of the following correctly describes a method of chemical control used to control microbial growth?
Surface-active agents, or surfactants, decrease surface tension among molecules of liquid. Phenolics exert antimicrobial activity by injuring lipid-containing plasma membranes, which causes the cellular components to leak out of the cell. Alcohols exert their action by denaturing proteins and dissolving lipids.
Disinfectants known as (alcohols/oxidizers/aldehydes) have the chemical group -CHO, which reacts with and damages both proteins and nucleic acids.
aldehydes
Disinfecting agents naturally produced by microorganisms are
antibiotics
The use of lysozome during the preparation of cheese and wines is effective in reducing the numbers of
bacteria
Air can be disinfected using
both HEPA filters and ultraviolet light
Alcohols are used for antisepsis disinfection sterilization both sterilization and disinfection both antisepsis and disinfection
both antisepsis and disinfection
An antimicrobial agent that _ will have the most lasting germicidal effect.
damages DNA
A nurse preparing a section of skin for an inject is an example of
degerming
Physical removal of microbes without killing them is
degerming
Which of the following could be used to sterilize a heat-sensitive liquid such as urea broth? autoclaving lyophilization pasteurization filtration
filtration
Where are you likely to find an autoclave?
in dentist office
Heavy metal and oxidizing agent disinfectants damage (proteins/DNA/membranes), interfering with microbial metabolism.
proteins
Which of the following is a low-level disinfectant? oxidizing agents alcohols quats halogens
quats Alcohols and halogens are both intermediate-level disinfectants, and oxidizing agents are considered to be high-level disinfectants. Quarternary ammonia compounds are less effective.
The compound ethylene oxide is used in
sterilization
The process of incineration is used for
sterilization
