Microbiology An Introduction 10th Edition Tortora Case Funke Instructors Manual
Microbiology An Introduction 10th Edition Tortora Case Funke Test Bank
Microbiology An Introduction 10th Edition Tortora Case Funke Test Bank
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Free Nursing Test Questions:
6: Microbial Growth
6-1 Classify microbes into five groups on the basis of preferred temperature range.
6-2 Identify how and why the pH of culture media is controlled.
6-3 Explain the importance of osmotic pressure to microbial growth.
6-4 Name a use for each of the four elements (carbon, nitrogen, sulfur, and phosphorus) needed in large amounts for microbial growth.
6-5 Explain how microbes are classified on the basis of oxygen requirements.
6-6 Identify ways in which aerobes avoid damage by toxic forms of oxygen.
6-7 Describe the formation of biofilms and their potential for causing infection.
6-8 Distinguish chemically defined and complex media.
6-9 Justify the use of each of the following: anaerobic techniques, living host cells, candle jars, selective and differential media, enrichment medium.
6-10 Differentiate biosafety levels 1, 2, 3, and 4.
6-11 Define colony.
6-12 Describe how pure cultures can be isolated by using the streak plate method.
6-13 Explain how microorganisms are preserved by deep-freezing and lyophilization (freeze-drying).
6-14 Define bacterial growth, including binary fission.
6-15 Compare the phases of microbial growth, and describe their relation to generation time.
6-16 Explain four direct methods of measuring cell growth.
6-17 Differentiate direct and indirect methods of measuring cell growth.
6-18 Explain three indirect methods of measuring cell growth.
Check Your Understanding
Why are hyperthermophiles that grow at temperatures above 100°C seemingly limited to oceanic depths?
Other than controlling acidity, what is an advantage to using phosphate salt buffers in growth media?
Why might primitive civilizations have used food preservation techniques that rely on osmotic pressure?
If bacterial cells were given a sulfur source containing radioactive sulfur (35S) in their culture media, in what molecules would the 35S be found in the cells?
How would one determine whether a microbe is a strict anaerobe?
Oxygen is so pervasive in the environment that it would be very difficult for a microbe to always avoid physical contact. What, therefore, is the most obvious way for a microbe to avoid damage?
Identify a way in which pathogens find it advantageous to form biofilms.
Could humans exist on chemically defined media, at least under laboratory conditions?
Could Louis Pasteur, in the 1800s, have grown rabies viruses in cell culture instead of in living animals?
What BSL is your laboratory?
Can you think of any reason why a colony does not grow to an infinite size, or at least fill the confines of the Petri plate?
Could a pure culture of bacteria be obtained by the streak plate method if there were only one desired microbe in a bacterial suspension of billions?
If the Space Station in Earth orbit suddenly ruptured, the humans on board would die instantly from cold and the vacuum of space. Would all the bacteria in the capsule also be killed?
Can a complex organism, such as a beetle, divide by binary fission?
If two mice started a family within a fixed enclosure, with a fixed food supply, would the population curve be the same as a bacterial growth curve?
Why is it difficult to measure realistically the growth of a filamentous mold isolate by the plate count method?
Direct methods usually require an incubation time for a colony. Why is this not always feasible for analysis of foods?
If there is no good method for analyzing a product for its vitamin content, what is a feasible method of determining the vitamin content?
New in this Edition
- A significantly updated and expanded discussion of biofilms (which previously appeared in Chapter 27).
- A discussion of biosafety levels with a figure illustrating Biosafety Level 4
- A new Clinical Focus (MMWR) box illustrating the role of biofilms in causing nosocomial infections
The Requirements for Growth (pp. 157–163)
- The growth of a population is an increase in the number of cells.
- The requirements for microbial growth are both physical and chemical.
Physical Requirements (pp. 157–160)
- On the basis of preferred temperature ranges, microbes are classified as psychrophiles (cold-loving), mesophiles (moderate-temperature–loving), and thermophiles (heat-loving).
- The minimum growth temperature is the lowest temperature at which a species will grow, the optimum growth temperature is the temperature at which it grows best, and the maximum growth temperature is the highest temperature at which growth is possible.
- Most bacteria grow best at a pH value between 6.5 and 7.5.
- In a hypertonic solution, most microbes undergo plasmolysis; halophiles can tolerate high salt concentrations.
Chemical Requirements (pp. 160–162)
- All organisms require a carbon source; chemoheterotrophs use an organic molecule, and autotrophs typically use carbon dioxide.
- Nitrogen is needed for protein and nucleic acid synthesis. Nitrogen can be obtained from the decomposition of proteins or from NH4+ or NO3–; a few bacteria are capable of nitrogen (N2) fixation.
- On the basis of oxygen requirements, organisms are classified as obligate aerobes, facultative anaerobes, obligate anaerobes, aerotolerant anaerobes, and microaerophiles.
- Aerobes, facultative anaerobes, and aerotolerant anaerobes must have the enzymes superoxide dismutase (2 O2– + 2 H+ æÆ O2 + H2O2) and either catalase (2 H2O2 æÆ 2 H2O + O2) or peroxidase (H2O2 + 2 H+ æÆ 2 H2O).
- Other chemicals required for microbial growth include sulfur, phosphorus, trace elements, and, for some microorganisms, organic growth factors.
Biofilms (pp. 162–163)
- Microbes adhere to surfaces and accumulate as biofilms on solid surfaces in contact with water.
- Biofilms form on teeth, contact lenses, and catheters.
- Microbes in biofilms are more resistant to antibiotics than are free swimming microbes.
Culture Media (pp. 164–169)
- A culture medium is any material prepared for the growth of bacteria in a laboratory.
- Microbes that grow and multiply in or on a culture medium are known as a culture.
- Agar is a common solidifying agent for a culture medium.
Chemically Defined Media (p. 165)
- A chemically defined medium is one in which the exact chemical composition is known.
Complex Media (p. 165)
- A complex medium is one in which the exact chemical composition varies slightly from batch to batch.
Anaerobic Growth Media and Methods (pp. 166–167)
- Reducing media chemically remove molecular oxygen (O2) that might interfere with the growth of anaerobes.
- Petri plates can be incubated in an anaerobic jar, anaerobic chamber, or OxyPlate.
Special Culture Techniques (pp. 167–168)
- Some parasitic and fastidious bacteria must be cultured in living animals or in cell cultures.
- CO2 incubators or candle jars are used to grow bacteria that require an increased CO2 concentration.
- Procedures and equipment to minimize exposure to pathogenic microorganisms are designated as biosafety levels 1 through 4.
Selective and Differential Media (pp. 168–169)
- By inhibiting unwanted organisms with salts, dyes, or other chemicals, selective media allow growth of only the desired microbes.
- Differential media are used to distinguish different organisms.
Enrichment Culture (p. 169)
- An enrichment culture is used to encourage the growth of a particular microorganism in a mixed culture.
Obtaining Pure Cultures (pp. 169–170)
- A colony is a visible mass of microbial cells that theoretically arose from one cell.
- Pure cultures are usually obtained by the streak plate method.
Preserving Bacterial Cultures (p. 170)
- Microbes can be preserved for long periods of time by deep-freezing or lyophilization (freeze-drying).
The Growth of Bacterial Cultures (pp. 171–179)
Bacterial Division (p. 171)
- The normal reproductive method of bacteria is binary fission, in which a single cell divides into two identical cells.
- Some bacteria reproduce by budding, aerial spore formation, or fragmentation.
Generation Time (p. 171)
- The time required for a cell to divide or a population to double is known as the generation time.
Logarithmic Representation of Bacterial Populations (pp. 171–172)
- Bacterial division occurs according to a logarithmic progression (two cells, four cells, eight cells, and so on).
Phases of Growth (pp. 172–174)
- During the lag phase, there is little or no change in the number of cells, but metabolic activity is high.
- During the log phase, the bacteria multiply at the fastest rate possible under the conditions provided.
- During the stationary phase, there is an equilibrium between cell division and death.
- During the death phase, the number of deaths exceeds the number of new cells formed.
Direct Measurement of Microbial Growth (pp. 174–178)
- A standard plate count reflects the number of viable microbes and assumes that each bacterium grows into a single colony; plate counts are reported as number of colony-forming units (CFU).
- A plate count may be done by either the pour plate method or the spread plate method.
- In filtration, bacteria are retained on the surface of a membrane filter and then transferred to a culture medium to grow and subsequently be counted.
- The most probable number (MPN) method can be used for microbes that will grow in a liquid medium; it is a statistical estimation.
- In a direct microscopic count, the microbes in a measured volume of a bacterial suspension are counted with the use of a specially designed slide.
Estimating Bacterial Numbers by Indirect Methods (pp. 178–179)
- A spectrophotometer is used to determine turbidity by measuring the amount of light that passes through a suspension of cells.
- An indirect way of estimating bacterial numbers is measuring the metabolic activity of the population (for example, acid production or oxygen consumption).
- For filamentous organisms such as fungi, measuring dry weight is a convenient method of growth measurement.
Appendix B, “Exponents, Exponential Notation, Logarithms, and Generation Time,” is useful here. Bioenhancement with N and P is described in the box in Chapter 2, p. 33. The use of MPN in water quality testing is discussed on p. 175 and Figure 6.19.
- In binary fission, the cell elongates and the chromosome replicates. Next, the nuclear material is evenly divided. The plasma membrane invaginates toward the center of the cell. The cell wall thickens and grows inward between the membrane invaginations; two new cells result.
- Carbon: Synthesis of molecules that make up a living cell. Hydrogen: Source of electrons and component of organic molecules. Oxygen: Component of organic molecules; electron acceptor in aerobes. Nitrogen: Component of amino acids. Phosphorous: In phospholipids and nucleic acids. Sulfur: In some amino acids.
- a. Catalyzes the breakdown of H2O2 to O2 and H2O.
- H2O2; peroxide ion is O22–.
- Catalyzes the breakdown of H2O2;
NADH + H+ + H2O2 Peroxidase > NAD+ + 2H2O
- O2–; this anion has one unpaired electron.
- Converts superoxide to O2 and H2O2;
2O2– + 2H+ Superoxide dismutase > O2 + H2O2
The enzymes are important in protecting the cell from the strong oxidizing agents, peroxide and superoxide, that form during respiration.
- Direct methods are those in which the microorganisms are seen and counted. Direct methods are direct microscopic count, plate count, filtration, and most probable number. Growth is inferred by indirect methods: turbidity, metabolic activity, and dry weight.
- The growth rate of bacteria slows down with decreasing temperatures. Mesophilic bacteria will grow slowly at refrigeration temperatures and will remain dormant in a freezer. Bacteria will not spoil food quickly in a refrigerator.
- Number of cells x 2n generations = Total number of cells
6 x 27 = 768
- Petroleum can meet the carbon and energy requirements for an oil-degrading bacterium; however, nitrogen and phosphate are usually not available in large quantities. Nitrogen and phosphate are essential for making proteins, phospholipids, nucleic acids, and ATP.
- A chemically defined medium is one in which the exact chemical composition is known. A complex medium is one in which the exact chemical composition is not known.
- a. At x, the bacteria began a second lag phase during which they synthesized enzymes required to use the second carbon source.
- The first substrate provided the better growth conditions. The slope of the line is steeper, indicating that the bacteria grew faster.
- In the presence of oxygen, H2O2 forms in Clostridium. The H2O2 accumulates in these catalase-negative cells and kills them. H2O2 does not form in Streptococcus.
- Glucose provides a fermentable carbohydrate for chemoheterotrophs. Glucose is the carbon and energy source. Other macronutrients including nitrogen are provided in inorganic compounds in the “minimal salts.”
- a. A
- 1.68 x 108. They are the progeny of the original 10.
- At least 53°C; 60°C was recommended after this study. The bacteria get in the food during preparation and those buried inside do not get hot enough to be killed.
- Mouthwash 2 decreased bacterial numbers by 89% compared to a 17% decrease for both Mouthwash 1 and 3. All the bacteria probably did not grow. Only those that could grow aerobically on nutrient agar were counted in the experiment.
Case Study: Determining the Effectiveness of a Food Preservative
To determine whether a newly synthesized chemical might be a useful food preservative, the chemical was tested for its ability to inhibit bacterial growth.
500 ml of cottage cheese was inoculated with 2 ml of a 24-hr culture of Pseudomonas aeruginosa and incubated at 25°C. Five hours after inoculation, a standard plate count showed there were 200 bacterial cells/ml in the cottage cheese. After 29 hours at 25°C, there were 1,000,000 cells/ml in the cottage cheese.
500 ml of cottage cheese containing the preservative was inoculated with 2 ml of a 24-hr culture of P. aeruginosa. After 6 hours of incubation at 25°C, a standard plate count was performed. There were 700 bacterial cells/ml in the cottage cheese. After 38 hours, there were 61,000,000 bacterial cells/ml in the cottage cheese.
1.00 x 106 6.00
6.10 x 106 6.79
6.10 x 107 7.79
- Why were plate counts used instead of direct microscopic counts or turbidity measurements?
- How did the control cottage cheese and the experiment cottage cheese differ? Was this a fair test?
- Determine the effectiveness of the new food preservative.
- Does this type of test determine bacteriostatic or bactericidal activity?
- The particles in cottage cheese would interfere with direct counts and turbidity.
- The new chemical was added to the experiment and was lacking in the control. Yes, this is a fair test.
- The two tests had the same generation time, proving that the new food preservative was not effective.
- Both. The answer is “bactericidal” when the number of bacteria declines, and “bacteriostatic” if the number of bacteria stays the same.