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Questions and Answers
During which phase of the bacterial growth curve do bacteria increase in size without dividing?
During which phase of the bacterial growth curve do bacteria increase in size without dividing?
What occurs during the log phase of bacterial growth?
What occurs during the log phase of bacterial growth?
Which statement best describes what happens during the stationary phase of the bacterial growth curve?
Which statement best describes what happens during the stationary phase of the bacterial growth curve?
In which phase do bacteria exhibit features such as the production of granules and antibiotics?
In which phase do bacteria exhibit features such as the production of granules and antibiotics?
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What is the primary reason for the flat line observed in total count during the lag phase?
What is the primary reason for the flat line observed in total count during the lag phase?
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Which of the following statements is true regarding the viable count during the log phase?
Which of the following statements is true regarding the viable count during the log phase?
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Which phase of the bacterial growth curve is directly followed by the stationary phase?
Which phase of the bacterial growth curve is directly followed by the stationary phase?
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During which phase do bacteria primarily accumulate enzymes and metabolites in preparation for division?
During which phase do bacteria primarily accumulate enzymes and metabolites in preparation for division?
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Which characteristic is true during the stationary phase of bacterial growth?
Which characteristic is true during the stationary phase of bacterial growth?
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What is a key event that occurs during the stationary phase?
What is a key event that occurs during the stationary phase?
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Which of the following describes the decline phase of bacterial growth?
Which of the following describes the decline phase of bacterial growth?
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What occurs in bacterial cells during the stationary phase regarding storage?
What occurs in bacterial cells during the stationary phase regarding storage?
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Which type of bacteria can only grow when oxygen is present?
Which type of bacteria can only grow when oxygen is present?
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In which classification do bacteria grow well in low oxygen tension?
In which classification do bacteria grow well in low oxygen tension?
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What is a common characteristic of facultative anaerobes?
What is a common characteristic of facultative anaerobes?
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Which factor affecting bacterial growth does not directly relate to the nutrition available?
Which factor affecting bacterial growth does not directly relate to the nutrition available?
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What is the process called when dormant spores become active vegetative cells?
What is the process called when dormant spores become active vegetative cells?
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What is the typical shape and position of spores for a given bacterial species?
What is the typical shape and position of spores for a given bacterial species?
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Which of the following substances can effectively kill bacterial spores?
Which of the following substances can effectively kill bacterial spores?
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What appearance do spores have during Gram staining?
What appearance do spores have during Gram staining?
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Bacteria divide through which method of cell division?
Bacteria divide through which method of cell division?
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What is the minimum requirement for bacterial growth?
What is the minimum requirement for bacterial growth?
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How is 'generation time' defined in bacterial growth?
How is 'generation time' defined in bacterial growth?
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Which bacterial species' spores are used as indicators of proper sterilization for autoclaves?
Which bacterial species' spores are used as indicators of proper sterilization for autoclaves?
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Study Notes
Morphology of Bacteria
- Bacteria are classified based on shape and Gram staining properties.
- Cocci: Oval or spherical cells, arranged in clusters, pairs, or chains.
- Bacilli: Rod-shaped cells, arranged in chains, pairs, or curved forms (comma, cuneiform).
- Gram-positive cocci and bacilli exist in various arrangements (e.g., clusters, chains).
- Gram-negative cocci and bacilli are also present in distinct arrangements. Examples include pairs, lens shapes, and kidney shapes.
Bacterial Cell Wall and Appendages
- The outer layer/envelope comprises rigid cell walls and plasma membranes.
- Bacteria’s cytoplasm contains cytoplasmic inclusions (e.g., mesosomes, ribosomes), and a diffuse nucleoid with a single circular chromosome.
- Cell wall appendages (if present) include capsules, flagella, and fimbriae.
Bacterial Growth Curve
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A bacterial growth curve shows the growth progression over time, and has four phases.
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Lag phase: The time lag between inoculation and beginning of growth. Bacteria increase in size, accumulate enzymes and metabolites.
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Log phase: Exponential cell division, rapid growth. Bacteria are smaller, active, and uniformly stained.
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Stationary phase: Cell division rate declines as the rate of cell death increases. There’s a balance between dying and new cells.
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Decline phase: The cells stop dividing, while cell death continues as nutrients are depleted and toxic substances accumulate.
Bacterial Cell Anatomy
- The cell wall, a tough and rigid structure, surrounds the bacterium. It's 10–25 nm thick and accounts for 20–25% of the bacterial cell’s dry weight.
- The cell wall functions to protect the cell from osmotic lysis, provide rigidity, shield it from toxic substances, and act as a target for some antibiotics.
- The cell wall contains peptidoglycan. Gram-positive bacterial cell walls have thicker layers of peptidoglycan where as Gram-negative cell walls are thinner.
- The outer membrane in Gram-negative bacteria has a phospholipid layer, specialized proteins (OMPs or porin proteins), lipopolysaccharide (LPS), and a periplasmic space.
Types of Bacterial Motility
- Flagella: Thread-like structures that aid in motility, composed of a filament, basal body, and hook. Different arrangements for flagella exist: monotrichous, lophotrichous, peritrichous, and amphitrichous.
- Fimbriae or Pili: Short, hair-like structures for bacterial adhesion, and sometimes conjugation (sex pili).
Atypical Bacteria Patterns
- Involution forms: Swollen and aberrant forms resulting from aging cultures in high salt concentration, found in gonococci and Yersinia pestis.
- Pleomorphic bacteria: Exhibit shape and size variations in cells, including Proteus and Haemophilus.
- L-forms (Cell Wall-Deficient Forms): Discovered by E. Klieneberger. Associated with the persistence of pyelonephritis and chronic infections.
Bacterial Spores
- Spores are highly resistant, resting stages of bacteria, formed in unfavorable conditions.
- They are composed of several layers(core, cortex, coat, and exosporium).
- Sporulation (formation of spores) is a complex process and takes around 10 hours.
- Mature spores are resistant to heat and disinfectants.
- Spore germination turns the dormant spore into an active vegetative cell, driven by exposure to a nutrient rich environment.
Demonstration of Spores and Capsules
Methods exist to detect these structures in bacterial samples. One key method for capsules in the Quellung reaction. Other methods exist for detecting spores and capsules. Different staining methods may also be used.
Bacterial Growth Requirements
- Water constitutes 80% of the bacterial cell.
- Essential nutrients include carbon, nitrogen, hydrogen, oxygen, and some inorganic substances.
Bacterial Counts
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Total count: Measures the total number of bacteria (dead or alive) using methods like a counting chamber.
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Viable count: Measures living bacteria using techniques like the pour plate method.
Bacteria Classifications and Examples
There are various classifications for bacteria based on oxygen needs, temperature tolerance, and other factors. Specific examples are given for each classification.
Bacterial Growth Curve Phases
- Detailed study of the lag, log, stationary, and decline phases of bacterial growth with features and processes in each.
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Description
This quiz covers the morphology of bacteria, including classification based on shape and Gram staining properties. It also delves into the structure of bacterial cell walls and appendages, as well as the phases of the bacterial growth curve. Test your knowledge on these fundamental microbiology concepts.