Mastering Microbiology Chapter 6
(Q) Microbes have very narrow optimum temperature ranges. Which of the following classifications of microbes are most likely to cause human disease, based on temperature requirements? (1) mesophiles (2) hyperthermophiles (3) thermophiles (4) psychrophiles
Answer: (1) mesophiles. Extra: The temperature range of mesophiles overlaps that of normal human body temperature, allowing the greatest growth.
(Q) Which enzyme catalyzes the reaction: 2H2O2 → 2H2O + O2? A) Catalase B) Oxidase C) Peroxidase D) Superoxide dismutase
Answer: A) Catalase
(Q) A culture medium consisting of agar, peptone, and beef heart is a: A) complex medium. B) chemically defined medium. C) selective medium. D) reducing medium. E) differential medium.
Answer: A) complex medium.
(Q) Patients with indwelling catheters are susceptible to infections because: A. biofilms develop on catheters. B. injected solutions are contaminated. C. infections can be transmitted from other people. D. their immune systems are weakened. E. bacteria cause infections.
Answer: A. biofilms develop on catheters
(Q) During which growth phase will gram-positive bacteria be most susceptible to penicillin? A) Lag phase B) Log phase C) Death phase D) Stationary phase E) The culture is equally susceptible during all phases.
Answer: B) Log phase
(Q) Most fungi grow best at pH: A) 1. B) 5. C) 7. D) 9. E) 14.
Answer: B) pH 5 (Acidic)
(Q) The biosafety level for a clinical microbiology laboratory working with potentially airborne pathogens, like tuberculosis bacteria, is: A) BSL-1. B) BSL-2. C) BSL-3. D) BSL-4.
Answer: C) BSL-3.
(Q) Three cells with generation times of 60 minutes are inoculated into a culture medium. How many cells are there after 5 hours? A. 900 B. 180 C. 96 D. 32 E. 15
Answer: C. 96
(Q) Thirty-six colonies grew in nutrient agar from 1.0 ml of undiluted sample in a standard plate count. How many cells were in the original sample? A) 4 B) 9 C) 18 D) 36 E) 72
Answer: D) 36
(Q) An experiment began with 4 cells and ended with 128 cells. How many generations did the cells go through? A) 64 B) 32 C) 6 D) 5 E) 4
Answer: D) 5
(Q) A culture medium on which only gram-positive organisms grow and a yellow halo surrounds: Staphylococcus aureus colonies is called a(n): A) enrichment culture. B) selective medium. C) differential medium. D) selective and differential medium. E) differential and enrichment culture.
Answer: D) selective and differential medium.
(Q) If cells are grown in media containing amino acids labeled with radioactive nitrogen (15N), most of radioactivity will be found in the cells. A. DNA. B. proteins. C. phospholipids. D. DNA and proteins. E. DNA and phospholipids
Answer: D. DNA and proteins
(Q) T or F:
Answer: False
(Q) T or F: In performing a ten-fold dilutions series from a sample containing 10,000 bacteria per milliliter, the fourth tube in the dilution series will have 10 cells per milliliter.
Answer: False
(Q) T or F: Most pathogenic bacteria are thermophiles.
Answer: False
(Q) Which of the following is an advantage of the direct microscopic count? A) Can readily count organisms that are motile B) Enumerates dead cells C) Requires no incubation time D) Sample volume is unknown. E) Requires a large number of cells
Answer: C) Requires no incubation time
(Q) C) The same number of cells in both Assume you inoculated 100 cells into 100 ml of nutrient broth. You then inoculated 100 cells of the same species into 200 ml of nutrient broth. After incubation for 24 hours, you should have: A) More cells in the 100 ml. B) More cells in the 200 ml. C) The same number of cells in both.
Answer: C) The same number of cells in both.
(Q) C) The term facultative anaerobe refers to an organism that: A) Doesn't use oxygen but tolerates it. B) Is killed by oxygen. C) Uses oxygen or grows without oxygen. D) Requires less oxygen than is present in air. E) Prefers to grow without oxygen.
Answer: C) Uses oxygen or grows without oxygen.
(Q) A sample of milk is tested for its bacterial content in a plate count assay. A one-millileter 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: A. 540,000 cells. B. 540 cells. C. 54,000 cells. D. 54 cells. E. 5,400 cells.
Answer: C. 54,000 cells.
(Q) What enables the copied chromosomes to separate during binary fission? A. The septum splits the replicated chromosomes. B. The mitotic spindle drives the separation. C. The chromosomes are attached to different parts of cell membrane, which elongates and thus separates the chromosomes. D. The nuclear membrane dissolves.
Answer: C. The chromosomes are attached to different parts of cell membrane, which elongates and thus separates the chromosomes.
(Q) In one hospital, Pseudomonas aeruginosa serotype 10 infected the biliary tract of 10% 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 10 was not isolated from the detergent, glutaraldehyde, or tap water. What was the source of the infections? A. fecal contamination of the bile ducts B. bacterial cell walls in the water C. a biofilm in the reprocessor D. contaminated disinfectant
Answer: C. a biofilm in the reprocessor
(Q) Which of the following types of culture media would best be used by a veterinarian to grow any bacteria in a blood sample? A. selective and differential media B. general purpose media C. enrichment media D. selective media
Answer: C. Enrichment media
(Q) The source of nutrients in nutrient agar is: A) Agar. B) Nutrient. C) Peptone and beef extract. D) Peptone and NaCl.
Answer: C) Peptone and beef extract.
(Q) What Is Happening during Stationary Phase? 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. (1) Harmful waste products may be accumulating. (2) The number of cells that are dying is balanced by the number of new cells that are being formed. (3) Cells are not increasing in number because they have not yet adjusted to the nutrient availability in the new media. (4) The cells are likely running out of nutrients. (5) The cells are dead; therefore, the number is staying constant.
Answer: (1) Harmful waste products may be accumulating. (2) The number of cells that are dying is balanced by the number of new cells that are being formed. (4) The cells are likely running out of nutrients. Extra: 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. During log phase, bacteria are actively growing and metabolizing. If the bacteria are being cultured for industrial purposes, such as producing amino acids or some other desirable product, they are generally most productive during log phase. For this reason, it is desirable to extend or prolong log phase.
(Q) 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? (1) Hyperthermophiles (2) Facultative halophiles (3) Extremophiles (4) Psychrophiles (5) Mesophiles
Answer: (2) Facultative halophiles (4) Psychrophiles (5) Mesophiles Extra: 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]. More Extra: Growth of the fecal coliform bacteria in the lake involves more than just simple physical conditions. Nutrients must also be available to build and support the new cells. As such, we also must consider the chemical requirements associated with this outbreak.
(Q) 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? (1) The lake environment will support only the growth of obligate anaerobes. (2) The lake environment will support the growth of facultative anaerobes. (3) Fecal coliforms will need to acquire trace elements for growth in the lake environment. (4) Fecal coliforms will likely contain enzymes to counteract toxic oxygen forms. (5) Fecal coliforms will not need organic growth factors to grow in the lake environment.
Answer: (2) The lake environment will support the growth of facultative anaerobes. (3) Fecal coliforms will need to acquire trace elements for growth in the lake environment. (4) Fecal coliforms will likely contain enzymes to counteract toxic oxygen forms. Extra: 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. More Extra: Recall that fecal coliforms are generally found in the intestines of warm-blooded animals. As such, they are adapted to be a part of a specific community of gut flora. The coliform organisms in the Lake of the Ozarks now find themselves in a completely different environment and bacterial community.
(Q) Which of the following would you expect to be a function of MacConkey agar? Mark all that apply. (1) allow for the growth of all organisms in a sample regardless of nutritional requirements (2) allow for the growth of all organisms in a sample that require only the most common nutrients (3) inhibit the growth of certain bacteria (4) change the color of some organisms based on their metabolic characteristics
Answer: (3) inhibit the growth of certain bacteria (4) change the color of some organisms based on their metabolic characteristics
(Q) Bacteria that can grow in the presence or absence of oxygen (O2) are called _____. (1) facultative anaerobes (2) obligate anaerobes (3) microaerophiles (4) obligate aerobes
Answer: (1) facultative anaerobes. Extra: Facultative anaerobes are able to use oxygen if it is present but also to grow in the absence of oxygen, although with decreased efficiency.
(Q) Which of the following methods used to count microbes is correctly matched as direct or indirect? (1) filtration--direct method (2) dry weight--direct measurement (3) plate count--indirect measurement (4) turbidity--direct method
Answer: (1) filtration--direct method. Extra: A specific volume of fluid is filtered through a membrane, which is then placed on media and allowed to grow, representing a direct count of the viable cells.
(Q) For which of the following types of microbes would a microbiologist use culture techniques for living host cells? (1) obligate intracellular organisms, such as chlamydia and viruses (2) capnophiles (3) normal skin bacteria (4) Campylobacteria sp.
Answer: (1) obligate intracellular organisms, such as chlamydia and viruses. Extra: These organisms cannot grow on media but require living host cells when cultured.
(Q) Bacterial growth measures increases in the size of a(n) _____________, while the growth of a multicellular organism refers to an increase in the size of a(n) _____________. (1) population; individual organism (2) individual organism; population (3) eukaryotic cell; prokaryotic cell (4) prokaryotic cell; eukaryotic cell
Answer: (1) population; individual organism
(Q) A microbe reproduces by binary fission every 20 minutes under favorable conditions. How long would 10 generations take and how many bacteria would be present if all the conditions were just right? (1) 18 hours and 40 minutes, producing 1 million bacteria (2) 3 hours 20 minutes, producing 1,024 bacteria (3) 2 hours and 10 minutes, producing 1,048,576 bacteria (4) 24 hours, producing 262,144 bacteria
Answer: (2) 3 hours 20 minutes, producing 1,024 bacteria. Extra: The organism produced 210 over 10 generations, which would take a little over 3 hours and produce over a half million bacterial cells.
(Q) Prolonging Exponential Growth: 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? (1) Chemostats include detoxifying agents that inactivate growth-inhibiting toxins that develop during continued microbial growth. (2) Chemostats provide a continued source of fresh nutrients and remove wastes and dead bacterial cells. (3) Chemostats promote the formation of endospores, which enable the long-term survival of the bacteria. (4) Chemostats include growth-promoting agents that prolong microbial growth.
Answer: (2) Chemostats provide a continued source of fresh nutrients and remove wastes and dead bacterial cells.
(Q) Bacterial generation times are typically measured using which units of time? (1) Months (2) Hours (3) Days (4) Seconds
Answer: (2) Hours
(Q) Which of the following statements regarding infections involving biofilms is FALSE? (1) It is estimated that nearly 70% of all infections are caused by biofilms. (2) There is no way to prevent biofilms from developing on surfaces. (3) Microbes in biofilms are 1000x more resistant to antimicrobials than are independent organisms. (4) The majority of hospital acquired infections (nosocomial infections) are related to biofilms.
Answer: (2) There is no way to prevent biofilms from developing on surfaces. Extra: This is false. Antimicrobials can be applied to the surface of catheters and IV tubing to prevent biofilm development.
(Q) Which of the following describes the correct equation used to calculate generation time? (1)(Number of cells at time zero) - (Number of cells at the end of a specified time) (2) Number of generations (doublings)/Total time (3) Total time/Number of generations (doublings) (4) (Number of cells at the end of a specified time) - (Number of cells at time zero)
Answer: (2) Total time / Number of generations (doublings)
(Q) Which of the following phases of the bacterial growth curve is matched with the correct definition? (1) death phase--the phase where the curve is flat; microbial deaths balance the number of new cells (2) log phase--the phase where organisms are actively dividing and the generation time is constant (3) lag phase--the phase where the death of organisms exceeds the creation of new cells and the curve declines (4) stationary phase--the phase where cells are not dividing very rapidly as they acclimatize to a new environment
Answer: (2) log phase--the phase where organisms are actively dividing and the generation time is constant. Extra: This is the steep upward slope of the bacterial growth curve, where organisms are rapidly multiplying.
(Q) 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? (1) colony (2) infectious unit (3) biofilm (4) planktonic unit
Answer: (3) Biofilm. Extra: 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.
(Q) 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? (1) direct microscopic counts (2) plate count culture (3) filtration count culture (4) serial dilution count culture
Answer: (3) filtration count culture. Extra: 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.
(Q) 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? (1) complex culture medium (2) anaerobic culture medium (3) basic culture medium (4) enrichment culture medium
Answer: (4) Enrichment Culture Medium. Extra: 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.
(Q) Which of the following statements accurately describes the culture media necessary for growing Clostridium tetani? (1) Nutrient agar contains ingredients that combine with oxygen and remove it, creating an anaerobic environment. (2) A complex medium is one whose exact chemical composition is known. (3) A chemically defined medium is one made up of extracts such as those from yeasts, meat, or plants whose exact chemical composition may vary slightly. (4) Reducing media are complex media containing chemicals, such as thioglycolate, that combine with oxygen, creating an anaerobic environment.
Answer: (4) Reducing media are complex media containing chemicals, such as thioglycolate, that combine with oxygen, creating an anaerobic environment. Extra: This medium is used to create an anaerobic environment for obligate anaerobes.
(Q) Bacteria are said to exhibit logarithmic, or exponential, growth. What does that mean about the growth rate of bacterial populations? (1) Every new cell is capable of producing two daughter cells. (2) The population size increases by a power of two. (3) The number of new cells is proportional to the size of the population (the larger the population gets, the faster it grows). (4) Since each and every bacterial cell is capable of reproduction, the size of a bacterial population increases by a power of two. In effect, the larger a population gets, the faster it grows.
Answer: (4) Since each and every bacterial cell is capable of reproduction, the size of a bacterial population increases by a power of two. In effect, the larger a population gets, the faster it grows.
(Q) Which of the following factors may affect the generation time? (1) Temperature (2) Growth media used (3) Bacterial species plated (4) Temperature, growth media, and bacterial species are all examples of factors that can affect generation time.
Answer: (4) Temperature, growth media, and bacterial species
(Q) 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? (1) The medium contains inhibitors that prohibit rapid growth of the bacteria, and these must be inactivated before bacterial numbers will increase. (2) The bacteria have to establish a biofilm before their numbers can increase. (3) There are not enough nutrients for the bacteria to grow, and growth is delayed until there are some dead cells to cannibalize. (4) The bacteria must adjust to the nutrient content in the new medium, synthesizing necessary amino acids, growth factors, and enzymes.
Answer: (4) The bacteria must adjust to the nutrient content in the new medium, synthesizing necessary amino acids, growth factors, and enzymes.
(Q) Which of the following statements describes what is happening in the cell during the lag phase? (1) Nutrients are depleted from the media; the microorganisms die at a rapid & uniform rate. (2) Cells are undergoing binary fission, resulting in an exponential increase in the population size. (3) The number of cells that are dividing equals the number of cells that are dying. (4) The cells are adjusting to their new environment; cellular metabolism is accelerated.
Answer: (4) The cells are adjusting to their new environment; cellular metabolism is accelerated.
(Q) Which of the following statements describes what is happening in the cell during the stationary phase? (1) The cells are adjusting to their new environment; cellular metabolism is accelerated. (2) Nutrients have been depleted from the media; the microorganisms are dying at a rapid and uniform rate. (3) Cells are undergoing binary fission, resulting in an exponential increase in the population size. (4) The number of cells that are dividing equals the number of cells that are dying.
Answer: (4) The number of cells that are dividing equals the number of cells that are dying.
(Q) What is the definition of generation time? 1) The time span from the beginning of the log phase to the beginning of the stationary phase 2)The time it takes for one bacterium to produce a new circular chromosome 3) The time span from the beginning of the lag phase and the beginning of the log phase 4) The time required for the population to double in size
Answer: (4) The time required for the population to double in size
(Q) Why are multiple serial dilutions plated when using the direct method? (1) So there are extra plates for comparison between the direct and indirect methods (2) In case one culture becomes contaminated (3) To compare rates of growth on different growth media (4) To ensure that one dilution results in a plate with a countable number of colony-forming units (cfu)
Answer: (4) To ensure that one dilution results in a plate with a countable number of colony-forming units (cfu)
(Q) The depletion of essential metabolites and accumulation of toxic metabolic waste products results in the beginning of the _________________ phase. (1) lag (2) stationary (3) log (4) death
Answer: (4) death
(Q) Which of the following statements describes what is happening in the cell during the logarithmic (log) phase? 1) Cells are undergoing binary fission, resulting in an exponential increase in the population size. 2) Nutrients have been depleted from the media; the microorganisms are dying at a rapid and uniform rate. 3) The cells are adjusting to their new environment; cellular metabolism is accelerated. 4) The number of cells that are dividing equals the number of cells that are dying.
Answer: 1) Cells are undergoing binary fission, resulting in an exponential increase in the population size.
(Q) Which of the following represents an ideal number of colony-forming units for effective enumeration using the direct method? (1) 1,000,000 (2) 100 (3) 1,000 (4) 10
Answer: 100
(Q) Calculating Population Increases during Exponential Growth: 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? (1) 32 million (2) 8 million (3) 16 million (4) 2 million (5) 4 million
Answer: 16 million. Extra 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
(Q) Starting with three cells, how many cells would result from three rounds of replication? A. Six B. Nine C. Twelve D. Twenty-four E. Forty-eight
Answer: 24
(Q) In microbiology lab, you make three different culture plates: one general purpose plate, one selective media plate, and one differential media plate. Unfortunately, you forget to label the different plates, so you do not know which is which. To determine the identity of each plate, you inoculate it with two different strains of laboratory bacteria. Which of the following results would indicate the plate you used was the general purpose media? A. Both organisms would grow equally well. B. Only one organism would grow. C. Both organisms would grow, but they would be dyed different colors. D. Only one organism would grow, and it would grow a different color.
Answer: Both organisms would grow equally well.
(Q) What is the difference between the direct and indirect methods of determining generation time with a growth curve? 1) In the indirect method, only one plate is inoculated; in the direct method, several serial dilutions are plated. 2) In the indirect method, the cells are enumerated by determining colony-forming units on a Petri dish; in the direct method, the cell numbers are approximated using a spectrophotometer. 3) In the direct method, the cells are enumerated by determining colony-forming units on a Petri dish; in the indirect method, the cell numbers are approximated using a spectrophotometer. 4) In the direct method, only one plate is inoculated; in the indirect method, several serial dilutions are plated.
Answer: 3) In the direct method, the cells are enumerated by determining colony-forming units on a Petri dish; in the indirect method, the cell numbers are approximated using a spectrophotometer.
(Q) 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
Answer: 3-1-2-4
(Q) 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: A) 54 cells. B) 540 cells. C) 5400 cells. D) 54,000 cells. E) 540,000 cells.
Answer: 54,000 cells.
(Q) The addition of which of the following to a culture medium will neutralize acids? A) Buffers B) Sugars C) pH D) Heat E) Carbon
Answer: A) Buffers
(Q) Most bacteria reproduce by: A) binary fission. B) fragmentation. C) mitosis. D) aerial hyphae. E) budding.
Answer: A) binary fission.
(Q) Pathogenic bacteria isolated from the respiratory or intestinal tracts of humans are: A) capnophiles that grow best in carbon dioxide incubators. B) facultative anaerobes that require reducing media for growth. C) strict aerobes that grow best in candle jars. D) capnophiles that prefer highly oxygenated growth conditions. E) strict aerobes that grow best in reducing media.
Answer: A) capnophiles that grow best in carbon dioxide incubators.
(Q) How long does it take for the daughter cells from one round of replication to replicate themselves? A. 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. B. No time is needed -- the daughter cells cannot replicate further. C. 20 minutes D. After the cells have matured fully.
Answer: A. 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.
(Q) Which step of binary fission is the reason for genetically identical daughter cells? A. Replication of the bacterial chromosome B. Splitting of the two daughter cells C. Elongation of the cell D. There are four new daughter cells that result from one parental cell
Answer: A. Replication of the bacterial chromosome
(Q) Lag Phase: 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?
Answer: A. The bacteria must adjust to the nutrient content in the new medium, synthesizing necessary amino acids, growth factors, and enzymes. Extra: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.
(Q) What does a spectrophotometer directly measure? 1) Plate count in colony-forming units 2) Absorbance of light 3) Level of contamination 4) Bacterial growth
Answer: Absorbance of light
(Q) Which of these elements is NOT correctly matched with its cellular function? A) magnesium and potassium — required as cofactors for enzymes B) sulfur — used for synthesis of thiamin and biotin C) nitrogen — needed for amino acid synthesis D) phosphorus — incorporated into nucleic acids E) None of the answers is correct; all of the elements are correctly matched.
Answer: All of the answers are correctly matched.
(Q) Which of the following is the best definition of generation time? A) The length of time needed for lag phase B) The length of time needed for a cell to divide C) The minimum rate of doubling D) The duration of log phase E) The time needed for nuclear division
Answer: B) The length of time needed for a cell to divide
(Q) Which of the following is NOT a step in bacterial cell division? A. Cell elongation B. Disappearance of nuclear envelope C. Splitting apart of two new daughter cells D. Replication of the genetic material
Answer: B. Disappearance of nuclear envelope
(Q) What would happen if the septum did not form during binary fission? A. The chromosome could not replicate. B. The parent cell would now have two copies of the chromosome. C. Nothing; the septum is not required for binary fission. D. The daughter cells would not be genetically identical.
Answer: B. The parent cell would now have two copies of the chromosome.
(Q) The biosafety level (BSL) for most introductory microbiology laboratories is: A) BSL-1. B) BSL-2. C) BSL-3. D) BSL-4.
Answer: BSL-1
(Q) Which level of biosafety (BSL) is appropriate for handling organisms that present a moderate risk of infection? BSL-3 BSL-1 BSL-2 BSL-4
Answer: BSL-2. Extra: BSL-2 labs feature open bench tops, lab coats, gloves, and appropriate eyewear for use in working with microbes that are moderately pathogenic.
(Q) Which of the following is an advantage of the standard plate count? A) Can readily count cells that form aggregates B) Requires incubation time C) Determines the number of viable cells D) Chemical and physical requirements are determined by media and incubation. E) Cannot be used to count bacteria in food
Answer: C) Determines the number of viable cells
(Q) Which of the following is an example of a metabolic activity that could be used to measure microbial growth? A) MPN B) standard plate count C) glucose consumption D) turbidity E) direct microscopic count
Answer: C) Glucose Consumption
(Q) In microbiology lab, you make three different culture plates: one general purpose plate, one selective media plate, and one differential media plate. Unfortunately, you forget to label the different plates, so you do not know which is which. To determine the identity of each plate, you inoculate it with two different strains of laboratory bacteria. After inoculation, you see that a particular plate has allowed both organisms to grow, but one has changed color. Which plate do you think this is? A. It is impossible to distinguish between selective and differential media in this case. B. selective media C. differential media D. general purpose media
Answer: C. differential media
(Q) The term aerotolerant anaerobe refers to an organism that: A. uses oxygen or grows without oxygen. B. is killed by oxygen. C. does not use oxygen but tolerates it. D. requires more oxygen than is present in air. E. requires less oxygen than is present in air.
Answer: C. does not use oxygen but tolerates it
(Q) Salts and sugars work to preserve foods by creating: A) Depletion of nutrients. B) Hypotonic environment. C) Lower osmotic pressure. D) Hypertonic environment. E) Lower pH.
Answer: D) Hypertonic environment.
(Q) D) Metabolic activity Which of the following is NOT a direct method to measure microbial growth? A) Direct microscopic count B) Standard plate count C) Filtration D) Metabolic activity E) MPN
Answer: D) Metabolic activity
(Q) Which enzyme catalyzes the reaction: O2- + O2- + 2H+ → H2O2 + O2? A) Catalase B) Oxidase C) Peroxidase D) Superoxide dismutase
Answer: D) Superoxide dismutase
(Q) Which of the following pairs is mismatched? A) hyperthermophiles — growth at 85°C B) psychrotroph — growth at 0°C C) psychrophile — growth at 15°C D) thermophile — growth at 37°C E) mesophile — growth at 25°C
Answer: D) Thermophile → growth at 37°C
(Q) Which of the following is an organic growth factor? A) glucose B) NH₄H₂PO₄ C) peptone D) vitamin B1 E) H₂O
Answer: D) Vitamin B1
(Q) What results when a single bacterium reproduces? A. One parent cell and a genetically identical daughter cell B. One parent cell and a genetically different cell C. Two genetically identical daughter cells D. Two genetically unique daughter cells
Answer: D. Two genetically unique daughter cells
(Q) Which group of microorganisms is most likely to spoil a freshwater trout preserved with salt? A) thermophiles B) anaerobes C) psychrophiles D) hyperthermophiles E) facultative halophiles
Answer: E) Facultative Halophiles
(Q) If you begin with six cells, how many cells would you have after three rounds of division? A. Twelve cells B. Nine cells C. Eighteen cells D. Twenty-four cells E. Forty-eight cells F. It is impossible to determine.
Answer: E. Forty-eight cells
(Q) 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? (1) direct microscopic count (2) indirect estimate based on turbidity (3) plate count (4) Any of these methods will provide reliable data for plotting a growth curve. (5) electronic cell counter
Answer: 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.
(Q) Why must a new pipette be used for each dilution when plating a serial dilution? 1) To avoid contamination from non-sterile pipettes 2) To avoid contamination from environmental organisms 3) To make sure organisms from the previous dilution are not carried over into the next dilution 4) To practice proper pipetting techniques
Answer: To make sure organisms from the previous dilution are not carried over into the next dilution
(Q) T or F: Agar is used as a solidifying agent in microbiological media since few bacteria can degrade it.
Answer: True
(Q) T or F: An isolated colony on a streak plate contains millions or billions of identical cells.
Answer: True
(Q) T or F: Bacterial growth refers to an increase in the numbers of cells in a bacterial culture.
Answer: True
(Q) T or F: Filtration methods are used to count bacteria present in very low concentrations, such as in lakes and streams.
Answer: True
(Q) T or F: Laboratory cultivation of obligate anaerobes requires reducing media or special growth chambers filled with inert gases.
Answer: True
(Q) T or F: Nitrogen-fixing bacteria, such as cyanobacteria, can use atmospheric nitrogen (N 2 ) for their nitrogen source.
Answer: True
(Q) T or F: Turbidity is an indirect measurement of bacterial growth that can be measured using a spectrophotometer.
Answer: True
(Q) Most bacteria grow best at pH: A) 1. B) 5 C) 7. D) 9. E) 14.
Answer: c) pH 7 (Neutral)
(Q) Which process is best for the short-term storage of bacterial cultures? (1) lyophilization (2) deep-freezing (3) freeze-drying (4) refrigeration
Answer: refrigeration Extra: Refrigeration is the best short-term storage method for microbes. Refrigeration slows down metabolic activity, but the microbes can be quickly revived at optimum temperatures.
In the figure, which line best depicts a facultative anaerobe in the absence of O2?
b