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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 seven days the dry weight of fungi on the treated apples is 5 mg and 10 mg on the untreated apples. You conclude from these results that ________.
Since the treatment appears to have slowed fungal growth, we can say that it is fungistatic
Decimal reduction time is the time in minutes in which ________ of the population at a given temperature will be killed.
What is the difference between a disinfectant and an antiseptic?
Disinfectants are used on environmental surfaces; antiseptics are used on living tissue.
Which of these conditions is likely to interfere with the effectiveness of an antiseptic or disinfectant?
presence of biofilms
Which substance is effective against bacterial endospores?
Endospores are very difficult to destroy. Of the choices, chlorine bleach is the most effective.
Which concentration of ethyl alcohol is the most effective disinfectant?
Alcohols work by denaturing proteins, and this process requires water. Generally the most effective alcohol concentration is 70%.
Which of these organisms is the most difficult to destroy using either chemical or physical methods?
Which chemical is not an oxidizing agent?
Triclosan is not an oxidizing agent. Triclosan inhibits an enzyme required for the synthesis of membrane lipids.
The use-dilution values for three disinfectants tested under the same conditions are Disinfectant X-1:10; Disinfectant Y-1:100; Disinfectant Z-1:1,000. If the disinfectants are nontoxic and designed for the same purpose, which would you select?
The disinfectant with the greatest use-dilution value is the most effective.
The disk-diffusion test is used to test disinfectants against Staphylococcus aureus. For disinfectant A, a 1:10 dilution gives a 25-mm zone of inhibition; 1:100 has a 15-mm zone of inhibition; and 1:1000 gives a 0-mm zone of inhibition. For disinfectant B, a 1:10 dilution gives a 50-mm zone of inhibition; 1:100 has a 25-mm zone of inhibition; and 1:1000 gives a 10-mm zone of inhibition. Which disinfectant is most effective?
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 since dairy products typically must be kept cold to prevent spoilage. How were these products treated to eliminate microbial growth and prevent spoilage?
UHT is a treatment that essentially sterilizes the product.
Some antimicrobial treatments kill microbes; some inhibit growth. Which term refers to an agent that inhibits bacterial growth?
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 min. at 52°C; 3.7 min. at pH 2.6; 13.3 min. with 10 mM hydrogen peroxide; and > 35 days without treatment. Which treatment is most effective against S. enterica?
Pasteurized milk in an unopened container spoils in the refrigerator. A sample reveals the presence of microorganisms. The most likely explanation is ________.
the microbes that survived pasteurization were able to grow at 4°C.
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?
Prepare and autoclave the medium before adding the growth factors. After the medium has cooled, filter sterilize and aseptically add the growth factors.
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?
The following may be listed on the ingredients of your favorite snack food. Which of these products is not antimicrobial?
The presence of organic matter, such as blood or saliva, may impair the action of antimicrobial chemicals.
Times required for sterilization in an autoclave are shorter than those required in a dry oven because moist heat penetrates biological specimens more effectively than does dry heat.
Ethylene oxide gas is used to sterilize medical equipment that might be damaged by exposure to the heat of autoclaving.
UV radiation and x-ray radiation are similar in that they damage DNA and have a high penetrating power.
Iodine is one of the least effective antimicrobial chemicals, effective only against certain very sensitive strains of bacteria.
Soap is ineffective in killing bacteria. Therefore, hand washing is a rather ineffective measure in preventing disease transmission.
Ionizing radiation can be used to sterilize some foods such as spices, meat, and fruits and vegetables.
Put the following in order from least to greatest amount of time to kill the population using a chemical agent: gram-negative bacteria, gram-positive bacteria, endospores, mycobacteria.
gram-positive bacteria, gram-negative bacteria, mycobacteria, endospores
You have two populations of cells that you want to kill. The first has 100,000 cells per ml, and the second has 1,000,000 cells per ml. Which will be killed at a faster rate?
Both populations will be killed at the same rate.
What factors will play a role in the effectiveness of a treatment? Give an example.
Number of microbes, organic matter, temperature, biofilms, time of exposure to the treatment, characteristics of the microbe such as a capsule or being gram positive or gram negative, concentration of the chemical, and if it is a resistant organism.
How will actions of microbial control agents affect the bacteria?
Alteration of membrane permeability and damage to proteins by way of chemicals, heat, pressure, or adding metals. Also damage to the nucleic acids by adding chemicals or metals.
Lowest TEMPerature at which all cells in a culture are KILLED in 10 minutes
thermal death point, TDP
What are some characteristics of an autoclave?
Steam reaches 120 degrees Celsius, only for items that can get wet like glass, NO paper or plastic, kills microbes quickly, sterilization takes 15-20 minutes.
How does an autoclave affect the microbes?
The moist heat in the autoclave causes the proteins within the cell to denature.
Name four types of dry heat sterilization.
dry heat, oven
flaming, Bunsen burner
incineration, hot coils
What form of sterilization should you use if the substance cannot be heated, such as blood or plasma?
HEPA for air
Membrane filtration for liquids
Name four physical methods of microbial control.
Low temperature (refrigeration, deep-freeze, lyophilization)
High pressure (denatures proteins)
Desiccation (prevents metabolism)
Osmotic pressure (causes plasmolysis)
What are the factors that play a role in what you are disinfecting?
concentration of disinfectant
Give an example of ionizing radiation and its effect on microbes.
X-rays, gamma rays, electron beams
ionizes water to release OH
How do microwaves kill microbes?
The microwaves cause the water molecules within the microbes to move faster which causes them to heat up. Increasing the temperature denatures proteins.
What are phenols and phenolics and how do they effect the bacteria?
They are alcohols and they disrupt the plasma membrane. Alcohols such as ethanol denature proteins, dissolve lipids, and require water.
Differentiate between hot-air and autoclave sterilization.
Hot-air: dry, 170 degrees Celsius, takes 2 hours, used for paper and pipettes.
Autoclave: moist heat, 121 degrees Celsius, take 15 minutes, used for glass
What form of "cleaning" is the surface-active agent, surfactant, acid-anionic detergents?
What form of "cleaning" is the surface-active agent, surfactant, quarternary ammonium compounds? Also known as cationic detergents.
bactericidal, denature proteins, disrupt plasma membrane
What are gaseous sterilants used for? How do they work? Give an example.
Used for heat-sensitive material. They denature proteins. Example is ethylene oxide.
What are peroxygens used for? How do they work? Give an example.
Used on contaminated surfaces. It is an oxidizing agent. O3 (ozone), H2O2 (hydrogen peroxide)
List microbes in order from most resistant to least resistant.
endospore of bacteria
cysts of protozoa
fungi, including fungal spores
viruses without envelopes
viruses with lipid envelopes
How much bleach is added to one gallon of water in order to sterilize it?
CDC states 1/8 tsp for cloudy water, let sit for 45 minutes, smell the water, should smell like chlorine
Times required for sterilization in an autoclave are shorter than those required in a dry oven because . . .
moist heat penetrates biological specimens more effectively than does dry heat.
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