Deck 5: Control of Microbial Growth

Question 1

An agriculture extension agent is preparing pamphlets on prevent­ing the spread of disease. In the pamphlet, he must explain the appropriate situations for using disinfectants around the house. What situations should the agent discuss?

Answer 1

The disinfectants are used for the sterilization of surfaces of non-living objects (inanimate) such as floors and instruments. Examples include, phenol, quaternary ammonium compounds, and others.
Disinfectant agents are often used to disinfect the kitchen area because food is one of the common sources of infectious microbes in the household.
In the given case, the agent should describe the possible sources of microbial contamination in the kitchen and around the house, which include the food residues, contaminated foods, skin and respiratory secretions. Bedding and toiletries of people with infectious diseases should also be disinfected.

Question 2

This graph shows the time it takes to kill populations of the same microorganism under different conditions. What conditions would explain the differences in lines a, b, and c?

Answer 2

The given graph is showing the time taken to kill the microbes on the X-axis, and the number of surviving cells on the Y-axis.
From the graph, it can be observed that both the population "a" and "b" contain the same number of surviving bacteria, but it took more time to kill the bacteria from population a, than that of the population b (same number and type of bacteria). Means, the population b might have been subjected to more toxic or destructive condition (such as higher temperature, destructive radiation, or a greater germicide concentration) than population a.
The rate of death of population "a and c" is same, means they are subjected to equally toxic conditions. The difference between population a and c is, the population "c" started with low number of surviving cells and all the cells were killed within a short time period of time.

Question 3

The methods used to control microbial growth depend on the situation and the level of control required.
How is sterilization different from disinfection?

Answer 3

Sterilization is a process that destroys or removes all of the microorganisms or viruses on or contained in a material. This process is achieved by destroying microbes by heating them, filtration, irradiation, or by using specific chemicals. The sterilization process means that the microbes are destroyed to the point that they cannot multiply when they are moved from the sterilized material to a growth medium. Sterile materials refer to those that are completely free of microbes such as endospores and viruses; however, this process doesn't refer to the removal of prions, which are protein particles that cause infection and cannot be removed by standard sterilization processes.
Disinfection is a process that refers to the removal of most or all pathogens on or in a product. Generally, this means that antimicrobial chemicals are used, and some microorganisms may remain living. Antimicrobial chemicals that are used for disinfecting nonliving materials are called disinfectants , which are toxic to most living microorganisms and are therefore biocides. Germicides are antimicrobial chemicals that target microorganisms and viruses, and are known as bactericidal because they kill bacterial. Antimicrobial chemicals that are considered non-toxic and used on the skin are called antiseptics.
Therefore, the main difference between sterilization and disinfection is that sterilization will destroy microorganisms, other than prions, so that they are unable to multiply, while disinfection will remove most pathogens, but some microorganisms may remain living.

Question 4

Unlike a disinfectant, an antiseptic

A) sanitizes objects rather than sterilizes them.
B) destroys all microorganisms.
C) is non-toxic enough to be used on human skin.
D) requires heat to be effective.
E) can be used in food products.

Question 5

How is preservation different from pasteurization?

Question 6

As a microbiologist representing a food corporation, you have been asked to serve on a health food panel to debate the need for chemical preservatives in foods. Your role is to prepare a statement that compares the benefits of chemical preservatives and the risks. What points must you bring up that indicate the benefits of chemi­cal preservatives?

Question 7

This diagram shows the filter paper method used to evaluate the inhibitory effect of chemical agents, heavy metals, and antibiotics on bacterial growth. A culture of a test bacterium is spread uniformly over the surface of an agar plate. Small filter paper discs containing the material to be tested are then placed on the surface of the medium. A disc that has been soaked in sterile distilled water is sometimes added as a control. After incubation, a lawn (film of growth) will cover the plate, but a clear zone will surround those discs that contain an inhibitory compound. The size of the zone reflects several factors, one of which is the effectiveness of the inhibitory agent. What are two other factors that might affect the size of the zone of inhibition? What is the purpose of the control disc? If a clear area were apparent around the control disc, how would you interpret the observation?

Question 8

The methods used to control microbial growth depend on the situation and the level of control required.
Why would water treatment facilities be concerned about disinfection by-products?

Question 9

The D value is defined as the time it takes to kill

A) all bacteria in a population.
B) all pathogens in a population.
C) 99.9% of bacteria in a population.
D) 90% of bacteria in a population.
E) 10% of bacteria in a population.

Question 10

What is the most chemically resistant non-spore-forming bacterial pathogen?

Question 11

The methods used to control microbial growth depend on the situation and the level of control required.
Why would the term sterilization not encompass prions?

Question 12

Which of the following is the most resistant to destruction by chemicals and heat?

A) Bacterial endospores
B) Fungal spores
C) Mycobacterium tuberculosis
D) E. coli
E) HIV

Question 13

Explain why it takes longer to kill a population of 10 9 cells than it does to kill a population of 10 3 cells.

Question 14

The types and numbers of microorganisms initially present, environmental conditions, the potential risks associated with use of the item, and the composition of the item must all be considered when determining which sterilization or disinfection procedure to employ.
Describe three groups of microorganisms that are resistant to certain chemical treatments.

Question 15

Ultraviolet light kills bacteria by

A) generating heat.
B) damaging DNA.
C) inhibiting protein synthesis.
D) damaging cell walls.
E) damaging cytoplasmic membranes.

Question 16

What is the primary reason that wine is pasteurized?

Question 17

The types and numbers of microorganisms initially present, environmental conditions, the potential risks associated with use of the item, and the composition of the item must all be considered when determining which sterilization or disinfection procedure to employ.
Why do critical instruments need to be sterile, whereas semicritical instruments need only be free of viruses and vegetative bacteria?

Question 18

Which concentration of alcohol is the most effective germicide? a) 100% b) 75% c) 50% d) 25% e) 5%

Question 19

What is the primary reason that milk is pasteurized?

Question 20

The types and numbers of microorganisms initially present, environmental conditions, the potential risks associated with use of the item, and the composition of the item must all be considered when determining which sterilization or disinfection procedure to employ.
Would it be safe to say that if all bacterial endospores had been killed, then all other medically important microorganisms had also been killed?

Question 21

Which of the following can most reliably be used as a sterilant?

A) Alcohol
B) Phenolic compounds
C) Ethylene oxide gas
D) Iodine

Question 22

When canning, why are low-acid foods processed at higher tem­peratures than high-acid foods?

Question 23

Moist heat such as boiling water destroys most microbes. Pasteurization significantly reduces the numbers of heat-sensitive organisms. Autoclaves use pressurized steam to achieve high temperatures that kill microbes, including endospores. The commercial canning process is designed to destroy the endospores of Clostridium botulinum. Dry heat takes longer than moist heat to kill microbes.
Why is it important that the commercial canning process destroys the endospores of Clostridium botulinum?

Question 24

All of the following are routinely used to preserve foods except

A) high concentrations of sugar.
B) high concentrations of salt.
C) benzoic acid.
D) freezing.
E) ethylene oxide.

Question 25

How are heat-sensitive liquids sterilized?

Question 26

Moist heat such as boiling water destroys most microbes. Pasteurization significantly reduces the numbers of heat-sensitive organisms. Autoclaves use pressurized steam to achieve high temperatures that kill microbes, including endospores. The commercial canning process is designed to destroy the endospores of Clostridium botulinum. Dry heat takes longer than moist heat to kill microbes.
How does incineration destroy microbes?

Question 27

Aseptically boxed juices and cream containers are processed using which of the following heating methods?

A) Canning
B) High-temperature-short-time (HTST) method
C) Low-temperature-long-time (LTLT) method
D) Ultra-high-temperature (UHT) method

Question 28

How does microwaving a food product kill bacteria?

Question 29

Moist heat such as boiling water destroys most microbes. Pasteurization significantly reduces the numbers of heat-sensitive organisms. Autoclaves use pressurized steam to achieve high temperatures that kill microbes, including endospores. The commercial canning process is designed to destroy the endospores of Clostridium botulinum. Dry heat takes longer than moist heat to kill microbes.
Would pasteurization destroy endospores?

Question 30

Commercial canning processes are designed to ensure destruction of which of the following?

A) All vegetative bacteria
B) All viruses
C) Endospores of Clostridium botulinum
D) E. coli
E) Mycobacterium tuberculosis

Question 31

How is an iodophore different from a tincture of iodine?

Question 32

Filters can be used to remove microorganisms and viruses from liquids and air. Gamma radiation can be used to sterilize products and to decrease the number of microorganisms in foods. Ultraviolet light can be used to disinfect surfaces and air. Microwaves do not kill microbes directly but destroy them by the heat they generate. Extreme pressure can kill microorganisms.
What is the difference between the mechanism of a depth filter and that of a membrane filter?

Question 33

Which of the following is false?

A) A high-level disinfectant cannot be used as a sterilant.
B) Critical items must be sterilized before use.
C) Low numbers of endospores may remain on semicritical items.
D) Standard sterilization procedures do not destroy prions.
E) Quaternary ammonium compounds can be used to disinfect food preparation surfaces.

Question 34

Name two products commonly sterilized using ethylene oxide gas.

Question 35

Filters can be used to remove microorganisms and viruses from liquids and air. Gamma radiation can be used to sterilize products and to decrease the number of microorganisms in foods. Ultraviolet light can be used to disinfect surfaces and air. Microwaves do not kill microbes directly but destroy them by the heat they generate. Extreme pressure can kill microorganisms.
How does ultraviolet light kill microorganisms?

Question 36

Filters can be used to remove microorganisms and viruses from liquids and air. Gamma radiation can be used to sterilize products and to decrease the number of microorganisms in foods. Ultraviolet light can be used to disinfect surfaces and air. Microwaves do not kill microbes directly but destroy them by the heat they generate. Extreme pressure can kill microorganisms.
Why could sterilization by gamma irradiation be carried out even after packaging?

Question 37

Germicidal chemicals can be used to disinfect and, in some cases, sterilize, but they are less reliable than heat. They are especially useful for destroying microorganisms and viruses on heat-sensitive items and large surfaces.
Describe four factors to consider when selecting a germicide.

Question 38

Germicidal chemicals can be used to disinfect and, in some cases, sterilize, but they are less reliable than heat. They are especially useful for destroying microorganisms and viruses on heat-sensitive items and large surfaces.
Explain why it is essential to dilute iodophores properly.

Question 39

Germicidal chemicals can be used to disinfect and, in some cases, sterilize, but they are less reliable than heat. They are especially useful for destroying microorganisms and viruses on heat-sensitive items and large surfaces.
Why would a heavy metal be a more serious pollutant than most organic compounds?

Question 40

Preservation techniques slow or halt the growth of microorganisms to delay spoilage.
What is the most important function of nitrate in cured meat?

Question 41

Preservation techniques slow or halt the growth of microorganisms to delay spoilage.
How do high concentrations of sugar and salt preserve foods?

Question 42

Preservation techniques slow or halt the growth of microorganisms to delay spoilage.
Preservation by freezing is sometimes compared to drying. Why would this be so?