Bacterial Morphology and Growth Patterns

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Questions and Answers

During which phase of the bacterial growth curve do bacteria increase in size without dividing?

  • Lag phase (correct)
  • Stationary phase
  • Log phase
  • Phase of decline

What occurs during the log phase of bacterial growth?

  • Bacteria accumulate maximum size
  • Bacteria die at a constant rate
  • Bacteria divide exponentially (correct)
  • No increase in total count is observed

Which statement best describes what happens during the stationary phase of the bacterial growth curve?

  • Bacteria divide at an exponential rate
  • Viable count remains constant while total count increases
  • Total count increases while viable count decreases
  • Bacterial death exceeds division (correct)

In which phase do bacteria exhibit features such as the production of granules and antibiotics?

<p>Phase of decline (A)</p> Signup and view all the answers

What is the primary reason for the flat line observed in total count during the lag phase?

<p>Bacteria are only increasing in size (B)</p> Signup and view all the answers

Which of the following statements is true regarding the viable count during the log phase?

<p>Viable count increases considerably (C)</p> Signup and view all the answers

Which phase of the bacterial growth curve is directly followed by the stationary phase?

<p>Log phase (D)</p> Signup and view all the answers

During which phase do bacteria primarily accumulate enzymes and metabolites in preparation for division?

<p>Lag phase (C)</p> Signup and view all the answers

Which characteristic is true during the stationary phase of bacterial growth?

<p>There is a balance between dying cells and newly formed cells. (B)</p> Signup and view all the answers

What is a key event that occurs during the stationary phase?

<p>Production of exotoxins and antibiotics. (B)</p> Signup and view all the answers

Which of the following describes the decline phase of bacterial growth?

<p>Cell death continues due to nutrient exhaustion. (B)</p> Signup and view all the answers

What occurs in bacterial cells during the stationary phase regarding storage?

<p>Increase in the number of storage granules. (D)</p> Signup and view all the answers

Which type of bacteria can only grow when oxygen is present?

<p>Obligate aerobes. (C)</p> Signup and view all the answers

In which classification do bacteria grow well in low oxygen tension?

<p>Microaerophilic bacteria. (C)</p> Signup and view all the answers

What is a common characteristic of facultative anaerobes?

<p>They can grow both aerobically and anaerobically. (C)</p> Signup and view all the answers

Which factor affecting bacterial growth does not directly relate to the nutrition available?

<p>Light. (A)</p> Signup and view all the answers

What is the process called when dormant spores become active vegetative cells?

<p>Germination (C)</p> Signup and view all the answers

What is the typical shape and position of spores for a given bacterial species?

<p>Oval or spherical, constant position (C)</p> Signup and view all the answers

Which of the following substances can effectively kill bacterial spores?

<p>Ethylene oxide sterilizer (C)</p> Signup and view all the answers

What appearance do spores have during Gram staining?

<p>Colorless and refractile (B)</p> Signup and view all the answers

Bacteria divide through which method of cell division?

<p>Binary fission (D)</p> Signup and view all the answers

What is the minimum requirement for bacterial growth?

<p>Carbon, nitrogen, hydrogen, oxygen, and some inorganic elements (B)</p> Signup and view all the answers

How is 'generation time' defined in bacterial growth?

<p>The time required for a bacterium to give rise to two daughter cells (B)</p> Signup and view all the answers

Which bacterial species' spores are used as indicators of proper sterilization for autoclaves?

<p>Geobacillus stearothermophilus (B)</p> Signup and view all the answers

Flashcards

Bacterial Growth Curve

A graph showing the change in bacterial count over time, as bacteria are grown in a culture.

Lag Phase

The initial phase of bacterial growth where bacteria adjust to the environment but don't multiply.

Log Phase

The phase of rapid bacterial multiplication, and exponential growth.

Stationary Phase

The phase where bacterial growth rate equals the death rate.

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Decline Phase

The final phase of bacterial growth where the bacteria die at an accelerating rate.

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Total Count

The total number of bacteria (live and dead) in a sample

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Viable Count

The number of living bacteria in a sample

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Bacterial Count

Measures the number of bacteria in a sample. Can be total or viable.

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Gram-variable bacteria

Bacteria that stain inconsistently with the Gram stain method, exhibiting both Gram-positive and Gram-negative characteristics. This happens due to changes in cell wall structure.

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Storage Granules

Intracellular structures in bacteria that store reserve materials such as carbohydrates, lipids, or phosphate. They accumulate during the stationary phase.

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Sporulation

The process by which some bacteria form resistant spores to survive harsh conditions. It occurs in the stationary phase.

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Exotoxins

Toxic proteins released by bacteria into the surrounding environment during the stationary phase. They can damage host cells and cause disease.

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Oxygen Requirements

The specific oxygen concentration needed for bacterial growth. Bacteria can be categorized into aerobes, anaerobes or microaerophiles.

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Obligate Aerobe

A bacterium that requires oxygen for growth.

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Facultative Anaerobe

A bacterium that can grow both in the presence and absence of oxygen.

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Microaerophile

A bacterium that thrives at lower oxygen concentrations than normal air.

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Spore Resistance

Mature bacterial spores are incredibly resistant to heat and disinfectants, making them difficult to kill.

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Germination (Spore)

The process where a dormant bacterial spore transforms into an active vegetative cell when exposed to favorable conditions.

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Spore Position

The location of a spore within a bacterial cell is constant for a given species; it can be central, subterminal, or terminal.

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Spore Shape

Bacterial spores typically have a consistent oval or spherical shape for each species.

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Spore Size

The diameter of a spore can be either the same size or smaller than the width of the bacteria it's in.

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Sporicidal Agents

Chemicals or treatments capable of killing bacterial spores; examples include autoclaves and ethylene oxide sterilizers.

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Staining Spores

Special staining techniques, such as Schaeffer-Fulton and Moeller stains, are used to visualize bacterial spores which usually appear as unstained, refractile bodies.

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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

  • A bacterial growth curve shows the growth progression over time, and has four phases.

  • Lag phase: The time lag between inoculation and beginning of growth. Bacteria increase in size, accumulate enzymes and metabolites.

  • Log phase: Exponential cell division, rapid growth. Bacteria are smaller, active, and uniformly stained.

  • Stationary phase: Cell division rate declines as the rate of cell death increases. There’s a balance between dying and new cells.

  • 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

  • Total count: Measures the total number of bacteria (dead or alive) using methods like a counting chamber.

  • 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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