Chapter 3 Quiz Review
Which of the following statements is true?
Hypochlorite-based disinfectants are effective against a wider range of pathogens than quats. While quats are used widely as surface-active agents, they are not effective at eliminating endospores or mycobacteria. Concentrated hypochlorite-based disinfectants are sporicidal and also germicidal against mycobacteria. Return to Assignment
Starting with three cells, how many cells would result from three rounds of replication?
Twenty-four
In the figure, which line best illustrates the growth of a facultative anaerobe incubated aerobically?
a
In one hospital, Pseudomonas aeruginosa serotype 10 infected the biliary tract of 10 percent of 1300 patients who underwent gastrointestinal endoscopic procedures. After each use, endoscopes were washed with an automatic reprocessor that flushed detergent and glutaraldehyde through the endoscopes, followed by a tap water rinse. P. aeruginosa serotype 10 was not isolated from the detergent, glutaraldehyde, or tap water. What was the source of the infections?
a biofilm in the reprocessor
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 __________.
antisepsis Antisepsis is the destruction of vegetative pathogens on living tissue.
Which of the following pairs of terms is mismatched?
bacteriostatic - kills vegetative bacterial cells
Which of the following pairs is mismatched?
biguanide - sporocide
All of the following substances are used to preserve foods EXCEPT
biguanides.
Bone and tendons for transplant are decontaminated by
supercritical fluids.
Which of the following is the best definition of generation time?
the length of time needed for a cell to divide
Which of the following pairs of microbe classification terms and optimal growth temperatures is mismatched?
thermophile - growth at 37°C
Consider a culture medium on which only gram-positive organisms such as Staphylococcus aureus colonies can grow due to an elevated NaCl level. A yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the pH as a result and changing the color of a pH indicator chemical. This type of medium would be referred to as a(n)
selective and differential medium.
An isolated colony on a streak plate contains millions (or even billions) of identical cells all arising from one initial cell.
True
In addition to physical requirements, bacterial growth and multiplication also entails chemical requirements. Which of the following statements would accurately describe chemical requirements and conditions associated with growth in the Lake of the Ozarks environment? Select all of the following statements that are true regarding fecal coliforms in the Lake of the Ozarks.
- Fecal coliforms will need to acquire trace elements for growth in the lake environment - The lake environment will support the growth of facultative anaerobes - Fecal coliforms will likely contain enzymes to counteract toxic oxygen forms With chemical and physical requirements met, bacteria are able to replicate in their environment and potentially increase numbers enough to find or invade a new host.
After a period of rapid growth (log phase), bacterial growth rates will slow and enter the stationary phase. The number of viable cells no longer increases, but instead stays constant. In this activity you will indicate the statements that correctly describe what is happening during stationary phase. Select each statement that accurately describes what is happening to bacterial cultures during stationary phase.
- The number of cells that are dying is balanced by the number of new cells that are being formed -Harmful waste products may be accumulating -The cells are likely running out of nutrients During the stationary phase, the number of viable cells does not increase and remains constant, or stationary. This phase begins as the nutrient supply is depleted and/or waste products begin to accumulate at a toxic level.
You might not consider the Midwest when someone mentions a beach trip, but the Lake of the Ozarks is a hotspot in the United States. Centrally located in the heart of Missouri, the lake is a great gathering place for Middle America vacations. It is one of the largest human-created lakes, containing roughly 600 billion gallons of fresh water, spanning approximately 61,000 acres and about 1100 miles of shoreline. Flow of the lake water is controlled by the Bagnell Dam. AmerenUE operates the dam for electrical production, in conjunction with the Army Corps of Engineers, which monitors the dam for spill-off, reservoir, and commerce. In a typical year, the lake system boasts 3.5 million tourists from Memorial Day to Labor Day, drawing in millions of dollars in vacations, tourism, boating, golf, hotels, and entertainment. During the summers of 2009 to 2011, things have been different at the Lake of the Ozarks. Bacterial growths have been "blossoming" in the water, which have the potential to cause disease. As a result, repeated closures have been necessary, and the beaches have been much quieter. The Missouri Department of Natural Resources (MODNR) routinely tests the waters for safety by counting fecal coliform bacteria. Fecal coliforms are a collection of microorganisms that live in large numbers in the intestines of warm-blooded animals (including humans). The best-known member of this group is Escherichia coli, but not all E. coli fecal coliform strains cause disease. However, E. coli can act as a marker of other microbial pathogen levels in the water. The Lake of the Ozarks is a human-made lake, so it collects runoff from coal strip-mining, fertilizers, resort wastewaters, and septic drainages. The average lake temperature is between 10∘∘C and 21∘∘C. Consider the physical requirements for growth and multiplication that would allow fecal coliforms to "blossom" in the Lake of the Ozarks. Which of the following would accurately describe these organisms? Check all that apply.
-Facultative halophiles - Mesophiles -Psychrophiles The bacterial growth process depends on the microorganism's ability to adapt to environmental conditions. Being able to grow to larger numbers increases the chances for survival and spread to new hosts. Requirements for growth have led us to develop descriptive terms for the organisms that refer to temperature range [Chapter 6, section 6-1], pH range [Chapter 6, section 6-2], and pressure range [Chapter 6, section 6-3].
Antimicrobial treatments, such as heat or chemicals, kill cells over a period of time. A microbial death curve is a plot of this decrease in population size as the antimicrobial treatment does its job. Typically, the death curve shows a constant percentage of cells dying each minute. For example, if we start with a population of 1,000,000 cells, and 90% of those cells die in the first minute, then we'd be left with 100,000 cells going into the second minute. During the second minute, 90% of the remaining cells would then die, leaving us with 10,000 cells going into third minute. Plotting this death curve would initially show the population decreasing rapidly. But then the plot would flatten out along the x-axis—approaching, but in theory never quite reaching, a population of zero. In practice, microbe populations are eventually eliminated by antimicrobial treatments, but the shape of the death curve reveals an important property of microbial population control. If a treatment eliminates 90% of the microbes in the first minute, killing the remaining 10% takes several times longer! Because most of the cells are killed early in the treatment, microbial death curves typically plot the logarithm of the population size rather than the actual (arithmetic) population size. Using a logarithmic scale makes it easier to visualize the population changes at late time points—the same data points that would otherwise be compressed down against the x-axis. 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?
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 surviving after 4 minutes is 1000
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?
10^5 After another 2 minutes of antimicrobial treatment, the population would be reduced to 105 cells (100,000). For a given period of treatment time, antimicrobial agents typically destroy a constant percentage of cells. In this example, the population was reduced by 90% in the first 2 minutes (i.e., from 107 to 106 cells, or 9,000,000 cells destroyed). Over the next 2 minutes, another 90% of the remaining 106 cells would be destroyed (i.e., 900,000 cells destroyed). This leaves 100,000 (105) cells surviving after a total of 4 minutes of treatmen
This activity asks you to calculate the size of a bacterial population during exponential growth. A broth medium has been inoculated, and microbial numbers will be counted periodically to generate a bacterial growth curve. At 2 hours after inoculation, the culture has progressed through lag phase and is now in log phase. At this point, the population size is 1 million cells. The generation time is 30 minutes. Assuming the continuation of log growth, how many cells would there be at 2 hours of growth in log phase?
16 million There would be approximately 16 million cells. In the 2-hour interval of log growth, there are four 30-minute generations. This is four doublings of the 1 million organisms present at hour 2.1 million cells x 24 = 16 million cells
The most resistant of the bacterial endospores can withstand boiling for up to
20 hours.
Put the following steps of bacterial replication in the correct order, starting from a parent cell. 1.Cell elongation 2.Septum formation 3.Chromosome replication 4. Separation of daughter cells
3, 1, 2, 4
A sample of milk is tested for its bacterial content in a plate count assay. A one-milliliter sample of the milk is diluted in a 1:10 dilution series. One milliliter of the third dilution tube is plated in a pour plate. After incubation, the plate has 54 colonies, indicating that the original milk sample contained
54,000 cells per milliliter.
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
Which concentration of ethanol is the most effective bactericide?
70 percent
Three cells with generation times of 60 minutes are inoculated into a culture medium. Assuming no lag phase takes place, how many cells are there after 5 hours?
96
In the figure, which line best depicts a psychrotroph incubated at 0°C?
?
Three different culture media are shown below. In the table, in which medium (or media) would an autotroph grow but a heterotroph could not?
A
Which of the following inanimate objects could ordinarily be treated with a low-level disinfectant?
A hospital scale A scale is considered a non-critical item as it only contacts the intact skin of a patient. Disinfectant with a low-level disinfectant is suitable to prevent the spread of pathogens.
Which of the following is an example of a healthcare-associated infection (HAI)?
A patient develops a Pseudomonas infection during treatment in a burn unit. Burns leave skin vulnerable to infections by bacteria like Pseudomonas aeruginosa. The presence of these microorganisms in the hospital environment makes these vulnerable patients susceptible to infection.
Which of the following regarding antimicrobial control agents is FALSE?
Alcohols effectively inactivate nonenveloped viruses by attacking lipids.
Which of the following factors contributes to the frequency of healthcare-associated infections (HAIs)?
All of the above Transmission from healthcare professionals to patients.The presence of patients with weakened immune systems.The presence of a wide range of pathogens in the healthcare environment. While any one of the factors cited may not be enough to cause infection, the convergence of all three factors place a patient at extreme risk of developing an HAI. Proper disinfection and sterilization is an important step in limiting the presence of microorganisms and cutting of the chain of transmission.
In the figure, which tube shows the expected growth pattern for a facultative anaerobe?
B
The biosafety level (BSL) for most introductory microbiology laboratories is
BSL-1
Which enzyme catalyzes the following reaction? 2H2O2 → 2H2O + O2
Catalase
A chemostat is continuous culture system that is designed to promote and prolong exponential growth and prevent bacteria from entering stationary phase. How might this work?
Chemostats provide a continued source of fresh nutrients and remove wastes and dead bacterial cells.
Which of the following regarding antimicrobial control agents is FALSE?
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. Any particular treatment may take a long time to eliminate all microbes from a sample. However, most of the cell death actually occurs early in the treatment. For example, if 90% of the population dies each minute, then it might take 6 minutes for an entire population of 1,000,000 cells to be eliminated. However, 90% of those cells—900,000—are killed in the very first minute. The remaining 100,000 die over the remaining 5 minutes. With a standard (arithmetic) graph, all the late data points are compressed down against the x-axis, making them hard to distinguish (blue trace; right y-axis). By displaying the logarithm of the data instead (red trace; left y-axis), both the early and late data points can be clearly seen.
How long does it take for the daughter cells to initiate or start the next round of replication?
No time is required -- they are ready to divide immediately after DNA replication and separation of the daughter cells is complete if conditions are right.
All of the following factors contribute to hospital-acquired infections EXCEPT
None of the answers is correct; all of these factors may contribute to hospital-acquired infection. - invasive procedures can provide a portal of entry for bacteria.some bacteria metabolize disinfectants.gram-negative bacteria are often resistant to disinfectants.bacteria may be present in commercial products such as mouthwash.
Which of the following statements accurately describes the culture medium necessary for growing an obligate anaerobe, such as Clostridium tetani?
Reducing media are complex media containing chemicals, such as thioglycolate, that combine with oxygen, creating an anaerobic environment. This medium is used to create an anaerobic environment for obligate anaerobes.
Which of the following is NOT a sign or symptom of a Clostridium difficile infection?
Respiratory distress Overgrowth of C. difficile in the colon results in the accumulation of toxins that cause inflammation of the colon (colitis). This inflammation results in bloody, watery stools (more than three times a day for at least three days), tenderness of the abdomen, and fever. It is a gastrointestinal infection, not a respiratory infection.
A sample of raw, unpasteurized milk is tested for its bacterial content in a plate count assay. A one-milliliter sample of the milk is diluted in a 1:10 dilution series. One milliliter of the third dilution tube is plated in a pour plate. After incubation, the plate has approximately 500 colonies, indicating that the original milk sample contained
The answer cannot be determined reliably with the information given.
When bacteria are inoculated into a new sterile nutrient broth, their numbers don't begin to increase immediately. Instead, there is a lag phase that may last for an hour or even several days. Why don't bacterial numbers increase immediately?
The bacteria must adjust to the nutrient content in the new medium, synthesizing necessary amino acids, growth factors, and enzymes. A new medium may not have the same nutrients that were available in the medium from which an inoculum was taken. The bacteria may have to synthesize different amino acids, growth factors, or enzymes to enable them to grow in this new medium. Once those are synthesized, the growth rate is likely to increase, and the cells will move into log (exponential) growth phase.
Which of the following best describes the pattern of microbial death?
The cells in a population die at a constant rate.
What enables the copied chromosomes to separate during binary fission?
The chromosomes are attached to different parts of cell membrane, which elongates and thus separates the chromosomes. Submit
This question asks you to make comparisons regarding the slope of an exponential growth curve, based on generation time. Each of the three graphs shown below includes data collected during exponential growth of a species of bacteria grown in three different growth conditions. Which growth condition resulted in the longest generation time?
The graph of exponential growth under growth condition C illustrates the slowest rate of growth and, thus, the longest generation time.
What would happen if the septum did not form during binary fission?
The parent cell would now have two copies of the chromosome.
Which of the following statements regarding infections involving biofilms is FALSE?
There is no way to prevent biofilms from developing on surfaces. This is false. Antimicrobials can be applied to the surface of catheters and IV tubing to prevent biofilm development.
Bacteria naturally prefer company instead of solitude for growth. Examples of this kind of communal growth pattern can be found everywhere, from surfaces of the teeth and the intestines, to the surface of a slimy rock in the lake, to the thick floc that clogs water pipes. These examples of communal bacterial growth are known by what name?
biofilm Biofilms are a large collection of mixed populations of organisms that form a matrix of "slime" for protection and assemble a complex, coordinated, and functional community on a surface. Biofilms often provide a safe haven for bacterial growth, often among "friendly" microorganisms. The complex architecture of biofilms gives the cells benefits they would not have in an individual lifestyle as a planktonic cell. As such, biofilms can play an extremely important role in colonizing a host and leading to a disease state.
Which of the following disinfectants acts by disrupting the plasma membrane?
bisphenols
All of the following are effective for destroying prions EXCEPT
boiling.
In the figure, which line shows the growth of an obligate aerobe incubated anaerobically?
c
The figure shows a typical bacterial growth curve with the y-axis indicating the log of the number of bacteria and the x-axis indicating time in culture. In the figure, which section (or sections) shows a growth phase where cells are dividing and dying, and the number of cells dying equals the number of cells dividing?
c
Which of the following substances is used for surgical hand scrubs?
chlorhexidine
A culture medium consisting of agar, peptone, and beef heart is a
complex medium.
Assume 109 E. coli cells/ml are in a flask.Which graph in the figure best depicts the effect of placing the culture at 7°C attime x?
d
Application of heat to living cells can result in all of the following EXCEPT
decreased thermal death time.
Which of the following is an advantage of the standard plate count?
determines the number of viable cells
Sampling lake water for microscopic organisms is not as easy as it sounds when you want to both count and identify species. In a given water sample, your bacteria of choice can be rare or difficult to culture, particularly given the mixture of bacteria in a biofilm. Which of the following culture media would be best for growing fecal coliforms when they are relatively less abundant than other bacteria in the lake?
enrichment culture medium Growth of microorganisms for identification is not a trivial exercise. To accurately and efficiently grow bacteria in culture, you must consider the bacteria's relative abundance, metabolic and chemical needs, and best growth conditions, as well as the cost and overall goals of the experiment. Enrichment culture medium is a good choice for environmental samples whose desired populations are low compared to the rest of the microbes present. From a sample of large numbers of organisms, complex medium favors the growth of only certain organisms.
Which group of microorganisms is most likely to spoil a freshwater trout preserved with salt?
facultative halophiles
Cultures of the Lake of the Ozarks water samples were grown on enrichment media for identification. However, these organisms are present to some degree in all samples. An important question from a clinical perspective is whether or not there is a significant increase in the fecal coliform populations that would put people's health at risk. If you were part of the team investigating this outbreak, how would you best enumerate the fecal coliform threat?
filtration count culture This method will trap organisms and keep them on the surface of the filter. Transferring the organisms to a plate will then produce an accurate count. Fecal coliform bacteria were counted by direct filtration CFUs. Some of the samples taken at the beaches exceeded the recommended maximum levels established by the Environmental Protection Agency (EPA) for direct sampling: greater than 235 E. coli per 100 ml of water, or a geometric mean of greater than 126 E. coli per 100 ml of water. The beach samples were 178.2 E. coli per 100 ml and 1299.7 E. coli per 100 ml, with a geometric mean of 173.2 E. coli per 100 ml.
The chemical requirements for microbial growth include carbon, nitrogen, phosphorus, and sulfur. Why do all cells need nitrogen?
for building amino acids, proteins, and nucleic acids Amino acids, proteins, and nucleic acids all include significant amounts of nitrogen.
Which of the following methods is used to preserve food by slowing the metabolic processes of foodborne microbes?
freezing
Which of the following could be used to sterilize plastic Petri plates in a plastic wrapper?
gamma radiation
Which of the following is an example of a metabolic activity that could be used to measure microbial growth?
glucose consumption
Salts and sugars work to preserve foods by creating a
hypertonic environment.
Which of the following phases of the bacterial growth curve is matched with the correct definition?
log phase--the phase in which organisms are actively dividing and the generation time is constant This is the steep upward slope of the bacterial growth curve, where organisms are rapidly multiplying.
Which of the following is the best method to sterilize heat-labile solutions?
membrane filtration
Microbial control methods usually target any of the following cellular components EXCEPT which one?
mitochondria Most of the target organisms are bacteria or viruses, which do not contain mitochondria. In addition, microbial control mechanisms attempt to target structures in microbes that are not common to human cells.
Which of the following does NOT achieve sterilization?
pasteurization
Disinfection of water is achieved by all of the following EXCEPT
peracetic acid.
Which enzyme catalyzes the reaction: H2O2 + 2H+ → 2H2O?
peroxidase
This activity asks you to consider various methods of counting or estimating the size of bacterial populations and to select the method that will provide the most accurate data for plotting a bacterial growth curve. Which of the following methods would be most appropriate for gathering data to plot a bacterial growth curve throughout the four phases?
plate count A plate count will provide the number of living cells. These data are most appropriate for generating a plot of a bacterial growth curve.
Which process is best for the short-term storage of bacterial cultures?
refrigeration Refrigeration is the best short-term storage method for microbes. Refrigeration slows down metabolic activity, but the microbes can be quickly revived when returned to optimum temperatures.
