Chapter 7: The Control of Microbial Growth

Any process that destroys the non-spore forming contaminants on inanimate objects is sterilization. True or False

False

Desiccation is a reliable form of sterilization. True or False

False

Which of the following methods is used to preserve food by slowing the metabolic processes of foodborne microbes? - pasteurization - ionizing radiation - lyophilization - freezing - nonionizing radiation

Freezing

A disk-diffusion test using Staphylococcus gave the following results: Disinfectant Zone of inhibition (mm) A 0 B 2.5 C 10 D 5 In the table, which compound was the most effective against E. coli? -A -B -C -D -The answer cannot be determined based on the information provided.

The answer cannot be determined based on the information provided.

Contaminated hospital equipment represents a difficult environment to control harmful microbial growth. Regarding influences that affect disinfection of hospital equipment, which of the following is an accurate statement? - Antimicrobial agents work best under reduced temperatures. - The presence of organic matter, such as dried blood or protein, will not affect the action of antimicrobial agents. - Biofilms, often found contaminating hospital equipment, are relatively simple targets for biocides to reach effectively. -The cell walls of gram-negative bacteria are especially resistant to many chemicals that are used destroy microbes.

The cell walls of gram-negative bacteria are especially resistant to many chemicals that are used destroy microbes. (A principal factor in this relative resistance to biocides is the external lipopolysaccharide layer of gram-negative bacteria.)

Moist heat destroys organisms by denaturing proteins. True or False

True

The thermal death time is the time needed to kill all the bacteria in a particular culture at a certain temperature. True or False

True

Prior to drawing blood for a blood donation, the nurse will clean the arm with a Betadine solution. This form of antimicrobial control is called __________. disinfection antisepsis sanitization sterilization

antisepsis: Antisepsis is the destruction of vegetative pathogens on living tissue.

Which of the following pairs of terms is mismatched? fungicide - kills yeasts and molds germicide - kills microbes bacteriostatic - kills vegetative bacterial cells sterilant - destroys all living microorganisms virucide - inactivates viruses

bacteriostatic - kills vegetative bacterial cells

Which of the following disinfectants acts by disrupting the plasma membrane? heavy metals halogens bisphenols soaps aldehydes

bisphenols

All of the following are effective for destroying prions EXCEPT NaOH + autoclaving at 134°C incineration boiling proteases None of the answers are correct; each of these will destroy prions.

boiling

Which of the following physical methods of microbial control denatures proteins as a mechanism of action? radiation incineration osmotic pressure boiling or autoclaving

boiling or autoclaving (Heat denatures proteins by altering the tertiary structure, inhibiting their function)

Which graph in the figure best depicts the effect of placing the culture at 7°C at time x? a b c d e

d

Application of heat to living cells can result in all of the following EXCEPT - damage to nucleic acids - alteration of membrane permeability - breaking of hydrogen bonds - decreased thermal death time - denaturation of enzymes

decreased thermal death time

The preservation of beef jerky from microbial growth relies on which method of microbial control? desiccation filtration ionizing radiation lyophilization supercritical CO2

desiccation

An agent used to reduce the number of bacteria on a toilet would most accurately be called a(n) disinfectant antiseptic aseptic virucide fungicide.

disinfectant

which of the following chemical agents is used for sterilization? alcohol phenolics chlorine soap ethylene oxide

ethylene oxide

Microorganisms placed in high concentrations of salts and sugars undergo lysis true or false

false

Ultraviolet light (UV) causes irreversible breaks in DNA strands. true or false

false

true or false The pH of the medium has no effect on the activity of the disinfectant being applied.

false

Which chemical disinfectant can be considered a sterilizing liquid agent when appropriately applied? ethylene oxide quaternary ammonium compounds sodium benzoate 70% ethanol gluteraldehyde

gluteraldehyde

Surface-active agents act by decreasing surface tension so that microbes can more easily be removed. All of the following agents use this mechanism of action EXCEPT __________. quaternary ammonium compounds (quats) acid-anionic sanitizers soaps and detergents halogens

halogens (This is the exception. The mechanism of action for halogens includes inhibiting protein synthesis and acting as a strong oxidizing agent, but halogens do not act as surface-active agents.)

The most effective form of chlorine is which of the following? chloromine hydrochloric acid hypochlorite ion hypochlorous acid ozone

hypochlorous acid

Gluteraldehyde is among the most effective chemical control agents because it __________. acts as a surfactant is useful for preserving food is considered a relatively safe sterilizing agent is oligodynamic

is useful for preserving food (Even in small concentrations, given adequate exposure time, gluteraldehyde inactivates microbial proteins and is considered bactericidal, tuberculocidal, virucidal, and sporicidal while being less irritating to living tissue. The fact that it is a liquid makes it extremely versatile agents for a variety of hospital equipment.)

Which of the following is the best method to sterilize heat-labile solutions? freezing membrane filtration autoclave dry heat pasteurization

membrane filtration

All of the following are methods of food preservation EXCEPT desiccation ionizing radiation high pressure microwaves osmotic pressure

microwaves

Microbial control methods usually target any of the following cellular components EXCEPT which one? nucleic acids mitochondria plasma membrane permeability microbial proteins

mitochondria

Which of the following does NOT achieve sterilization? supercritical fluids autoclave ethylene oxide dry heat pasteurization

pasteurization

Consider various effects of moist and dry heat to control microbial growth. Which of the following methods would best reduce the number of microbes without altering the taste and chemical composition of beer? boiling autoclaving hot-air sterilization pasteurization

pasteurization (Pasteurization retains the properties of the alcohol and the protein structure. Although it does not destroy all microbes, it is adequate to destroy most of the harmful microbes while retaining flavor.)

If you were preparing nutrient agar at home and did not have an autoclave, what could you use to sterilize the nutrient agar? oven at 121°C for one hour boiling for one hour hydrogen peroxide pressure cooker at 121°C for 15 minutes bleach

pressure cooker at 121°C for 15 minutes

Ethylene oxide is a

sterilizing agent

Autoclaving is the most effective method of moist heat sterilization. true or false

true

true or false? Pseudomonas has been found growing in quaternary ammonium compounds (quats).

true

true or false? Some antimicrobial chemicals are considered to be disinfectants and antiseptics.

true

Which of the following pairs is mismatched? ultraviolet radiation - desiccation supercritical fluids - CO2 plasma sterilization - free radicals ozone - takes electrons from substances ionizing radiation - hydroxyl radicals

ultraviolet radiation - desiccation

A kitchen countertop has a spill of vegetable oil that was wiped up but a film remains. What should be the next step in disinfecting this surface? warm soapy scrub chlorhexidine containing solution 10% bleach spray a disinfectant that contains a heavy metal isopropanol

warm soapy scrub

Which of the following treatments is the most effective for controlling microbial growth? - 140°C for 4 seconds - 63°C for 30 minutes - 72°C for 15 seconds - They are equivalent treatments -None of the answers is correct.

- 140°C for 4 seconds

Which of the following regarding antimicrobial control agents is FALSE? - Some agents kill by denaturing microbial cell proteins - Some agents affect microbial cell membranes by dissolving lipids - Silver-impregnated dressings are used for treating antibiotic-resistant bacteria - Contaminating organic debris such as blood or sputum decrease effectiveness - Alcohols effectively inactivate nonenveloped viruses by attacking lipids.

- Alcohols effectively inactivate nonenveloped viruses by attacking lipids.

Which of the following is a limitation of the autoclave? - It cannot be used with glassware - It cannot kill endospores - It cannot be used with heat-labile materials - It requires an excessively long time to achieve sterilization - It cannot inactivate viruses.

- It cannot be used with heat-labile materials

Which of the following is an example IS NOT 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 leftovers in the refrigerator after the meal.

- Mary warms food up in a microwave before putting it on the table

Which of the following regarding antimicrobial control agents is FALSE? - Some agents are utilized as both an antiseptic and a disinfectant - Some agents affect microbial cell membranes by dissolving lipids - Some agents kill by denaturing microbial cell proteins - Most chemical agents can achieve sterility - Contaminating organic debris such as blood or sputum will decrease effectiveness.

- Most chemical agents can achieve sterility

Which of the following best describes why microbial death curves are typically plotted logarithmically? - Most of the cell death occurs early in the treatment - Different treatments vary in the length of time required to kill all microbes - It takes longer to kill all members of a large population than a smaller one - Bacterial population sizes are typically expressed in logarithmic form.

- Most of the cell death occurs early in the treatment

All of the following factors contribute to hospital-acquired infections EXCEPT - bacteria may be present in commercial products such as mouthwash. - invasive procedures can provide a portal of entry for bacteria - gram-negative bacteria are often resistant to disinfectants - some bacteria metabolize disinfectants - None of the answers is correct; all of these factors may contribute to hospital-acquired infection.

- None of the answers is correct; all of these factors may contribute to hospital-acquired infection.

Which of the following correctly lists, in increasing order, the resistance of microorganisms to chemical biocides? - protozoan cysts, fungi, gram-negative bacteria, prions - prions, gram-negative bacteria, vegetative protozoa, gram-positive bacteria - gram-negative bacteria, fungi, protozoan cysts, mycobacteria - gram-positive bacteria, fungi, endospores, prions

- gram-positive bacteria, fungi, endospores, prions

An iodophor is a(n) - form of formaldehyde - iodine mixed with a surfactant - agent that reduces oxygen - quaternary ammonium compound - phenol

- iodine mixed with a surfactant

The fate of E. coli O157:H7 in apple cider held at 8°C for 2 weeks, with and without preservatives, is shown below: Bacteria/ml Cider only 2.2 Cider with potassium sorbate 2.0 Cider with sodium benzoate 0.5 Cider with potassium sorbate + sodium benzoate 0 In the table, which preservative is most effective? - potassium sorbate + sodium benzoate - no preservative - sodium benzoate - potassium sorbate

- potassium sorbate + sodium benzoate

When microbial control methods are used, microbes are destroyed at a constant rate; there is no instantaneous death of all the microbes present. That microbial death rate is influenced by all of the following factors EXCEPT __________. - the time of exposure - toxins produced by the microbe - the microbial characteristics - the number of microbes

- toxins produced by the microbe

A disk-diffusion test using Staphylococcus gave the following results: Disinfectant Zone of inhibition (mm) A 0 B 2.5 C 10 D 5 In the table, which compound was bactericidal? -A -B -C -D -The answer cannot be determined based on the information provided.

-The answer cannot be determined based on the information provided.

Which of the following best describes the pattern of microbial death? - The pattern varies depending on the antimicrobial agent - The pattern varies depending on the species - Not all of the cells in a culture are killed - All the cells in a culture die at once -The cells in a population die at a constant rate.

-The cells in a population die at a constant rate.

HEPA filters are effective because they are designed to remove all airborne particulates, including microorganisms down to 0.3 micrometers 10 micrometers 0.01 micrometers 1 micrometer 10 nanometers

0.3 micrometers

(use pic from que 7) A suspension of 106 Bacillus cereus endospores was put in a hot-air oven at 170°C. Plate counts were used to determine the number of endospores surviving at the time intervals shown. In the figure, the decimal reduction time (D value) for the culture, which is defined as the time to reduce a population by one log, is approximately 60 minutes 0 minutes 10 minutes 40 minutes 30 minutes.

10 minutes

que 14 add picture This graph shows a microbial death curve for a bacterial population subjected to a heat treatment. Treatment began at time zero. About how many cells were still living after 4 minutes of treatment? 3 cells 30 cells 1000 cells 10,000 cells

1000 cells (The 4-minute point on the graph indicates that the logarithm of the number of surviving cells is 3.0. Now, this is not the same as 3 cells, because the logarithm of 3 is not 3 [instead, log10(3) = 0.48]. It's the logarithm of 103 that's equal to 3.0. And 103 is the same as 1000. So the number of cells)

An antimicrobial chemical was added to a population of bacteria. The initial population was 107 living cells (10,000,000). After 2 minutes, only 106 cells still remained alive. After another 2 minutes (4 minutes of total treatment), about how many cells would still be alive? 0 10^3 10^4 10^5

10^3

7. (add picture) A suspension of 106 Bacillus cereus endospores was put in a hot-air oven at 170°C. Plate counts were used to determine the number of endospores surviving at the time intervals shown. In the figure, what is the thermal death time? 60 minutes 100°C 120 minutes 150°C The answer cannot be determined based on the information provided.

60 minutes

Which concentration of ethanol is the most effective bactericide? 70 percent 100 percent 30 percent 50 percent 40 percent

70 percent

Assume 109 E. coli cells/ml are in a flask. Which graph in the figure best depicts the effect of placing the culture in an autoclave for 15 minutes at time x?

B

A disk-diffusion test using Staphylococcus gave the following results: Disinfectant Zone of inhibition (mm) A 0 B 2.5 C 10 D 5 In the table, which compound was the most effective against Staphylococcus? -A -B -C -D -The answer cannot be determined based on the information provided.

C