Micro+Exam+2+Review-2

Chapter 4: Prokaryotic Structure

Cell Walls

• Gram-positive cell wall:

  • Composed of thick peptidoglycan layers.

  • Retains crystal violet stain, thus appearing purple under a microscope.

  • Biomedical significance: Provides structural support and protection to the cell; tends to be more susceptible to certain antibiotics (e.g., penicillin).

• Gram-negative cell wall:

  • Comprises a thinner peptidoglycan layer and an outer membrane.

  • Does not retain crystal violet stain, appearing pink after counterstaining with safranin.

  • Biomedical significance: Often more resistant to antibiotics due to the outer membrane, and can have toxic lipopolysaccharide (LPS) components.

Cell Wall Exceptions

• Mycolic acid (e.g., Mycobacterium, Nocardia):

  • A waxy substance that makes the cell wall resistant to decolorization.

  • Examples: Mycobacterium tuberculosis.

• Atypical cell walls (Archaebacterium):

  • Not classified as gram-positive or gram-negative; can be varied in structure.

  • Examples: Halobacterium.

• No cell wall (Mycoplasmas):

  • Lack a cell wall altogether, which provides unique adaptive features.

  • Example: Mycoplasma pneumoniae, causing atypical pneumonia.

• L Forms:

  • Variants of bacteria that lose their cell wall, allowing for survival under stress or antibiotic treatment.

Cell Membrane Composition and Function

• Composed of a phospholipid bilayer embedded with proteins.

• Functions:

  • Acts as a selective barrier regulating the entry and exit of substances in and out of the cell.

Page 2: Endospores

Endospore Formation

• Conditions promoting endospore formation:

  • Nutrient depletion, extreme temperatures, desiccation, or other adverse conditions.

Steps of Sporogenesis/Sporulation

1. DNA replication.

2. Cytoplasmic membrane invagination.

3. Formation of forespore.

4. Thickening of spore coat.

5. Water removal, resulting in dormancy.

Conditions for Spore Germination

• Stimuli: Nutrient availability and optimal temperature conditions.

Steps of Germination

1. Activation by heat or chemicals.

2. Water uptake and metabolic revival.

3. Outgrowth where the spore converts back to vegetative state.

Biomedical Significance of Spores

• Resistant to heat, desiccation, and antibiotics; can be a source of infection in humans.

Examples of Spore Formers

1. Bacillus anthracis (anthrax).

2. Clostridium tetani (tetanus).

3. Clostridium difficile (C. diff infections).

Page 3: Tetanus, Diphtheria, and Anthrax

Tetanus

• Organism: Clostridium tetani.

• Shape/Arrangement: Rod-shaped, anaerobic.

• Gram Reaction: Gram-positive.

• Oxygen Requirement: Obligate anaerobe.

• Transmission: Through contaminated wounds.

• Exotoxin: Tetanospasmin, causes muscle spasms.

Diphtheria

• Organism: Corynebacterium diphtheriae.

• Shape/Arrangement: Rod-shaped, club-like.

• Gram Reaction: Gram-positive.

• Oxygen Requirement: Aerobic.

• Transmission: Respiratory droplets.

• Exotoxin: Diphtheria toxin, inhibits protein synthesis.

Anthrax

• Organism: Bacillus anthracis.

• Shape/Arrangement: Rod-shaped, forms chains.

• Gram Reaction: Gram-positive.

• Oxygen Requirement: Aerobic.

• Transmission: Spores from infected animals or contaminated products.

• Exotoxin: Anthrax toxin, disrupts cell signaling.

Page 4: Pathogenicity and Toxins

Factors Leading to Anthrax’s Pathogenicity

• Spore formation, toxin production, and ability to evade immune response.

Comparison of Exotoxins and Endotoxins

• Exotoxins:

  • Composition: Proteins, secreted by living bacteria.

  • Heat Stability: Generally heat-labile.

  • Potency: Highly potent.

  • Specificity: Often specific to a particular host cell type.

  • Location: Secreted into the environment or released upon cell lysis.

• Endotoxins:

  • Composition: Lipopolysaccharides from the outer membrane of Gram-negative bacteria.

  • Heat Stability: Heat-stable.

  • Potency: Less potent than exotoxins.

  • Specificity: Less specific, affect a wide range of cells.

  • Location: Part of the bacterial cell wall, released upon cell division or lysis.

Comparison of Anti-Toxins, Vaccines, and Toxoid Vaccines

• Anti-Toxins: Passive immunity, immediate but temporary.

• Vaccines: Active immunity, long-lasting protection.

• Toxoid Vaccines: Inactivated toxins that stimulate an immune response without causing disease.

Chapter 7: Growth and Nutrition

Carbon and Energy Sources

• Carbon Source: Can be autotrophic (CO2) or heterotrophic (organic compounds).

• Energy Source: Can be phototrophic (light) or chemotrophic (chemical compounds).

Examples of Nutritional Types

• Photoautotrophs: Use light and CO2 (e.g., cyanobacteria).

• Chemoautotrophs: Use inorganic molecules (e.g., sulfur bacteria).

• Photoheterotrophs: Use light and organic compounds (e.g., purple non-sulfur bacteria).

• Chemoheterotrophs: Use organic compounds for both carbon and energy (e.g., most pathogenic bacteria).

Page 5: Transport Mechanisms

Energy Requirements and Movement

• Passive Transport (requires no energy):

  • Diffusion: Movement of molecules from high to low concentration.

  • Facilitated Diffusion: Movement with the help of protein channels.

• Active Transport (requires energy):

  • Movement against the concentration gradient.

Endocytosis

• Belongs to active transport as it requires energy to engulf substances.

Solutions and Cell Behavior

• Hypotonic: Cell swelling; possibly bursting if no cell wall.

• Isotonic: No net movement; stable condition.

• Hypertonic: Cell shrivels due to water loss.

Role of Metals in Microbial Growth

• Required as co-factors for enzymatic reactions and can act as antimicrobial agents (e.g., silver).

Page 6: Bacterial Growth Patterns

Bacterial Growth Conditions by Temperature

• Mesophile: Optimal growth at moderate temperatures (20-45°C).

• Psychrophile: Optimal growth at low temperatures (<20°C).

• Thermophile: Optimal growth at high temperatures (45-80°C).

• Thermoduric: Can survive high temperatures but do not grow at those temperatures.

Bacterial Growth Conditions by pH

• Acidophile: Thrives in acidic environments.

• Neutrophile: Thrives at neutral pH (6.5-7.5).

• Alkaliphile: Thrives in alkaline environments (above pH 9).

Gas Requirements

• Capnophiles: Require elevated concentrations of CO2 for growth.

Thioglycolate Broth Growth Illustration

• Aerobe: Grows at the top where oxygen is present.

• Facultative Anaerobe: Grows throughout but denser at the top.

• Microaerophile: Grows in the middle where oxygen concentration is lower.

• Anaerobe: Grows at the bottom away from oxygen.

• Aerotolerant Anaerobe: Grows evenly throughout, does not require oxygen but tolerates it.

Bacterial Growth Types

• Two main types: Lateral and exponential growth.

• Exponential Growth Calculation: 17 bacteria doubling every 30 minutes for 5 hours (10 periods of doubling) results in:

  • Final count = 17 * 2^10 = 17 * 1024 = 17408 bacteria.

Page 7: Turbidity and Dilution Factors

Turbidity Calculation

• OD of 0.5: Corresponds to approximately 1.5 x 10^8 cells/mL.

Dilution Factor for Plate 4

• Identify based on how dilutions were performed; typically reciprocal of dilution.

Colony Count Calculation

• 23 colonies on Plate 4; calculation for cells per mL based on plating volume and dilution factor needed.

Total Cell Estimate

• Total cells in original inoculum for 10 mL; calculates from colonies multiplying by dilution factors.

Expected Colony Counts on Other Plates

• Estimated based on dilutions, typically exponential; values derived from initial calculations.

Method Advantages and Disadvantages

• Advantages: Simplicity, cost-effectiveness, speed.

• Disadvantages: Possible inaccuracies, assumes uniform distribution of colonies.

Page 8: Cell Counting Methods

Filtration

• Advantage: Effective for concentrating microorganisms from large volumes.

• Disadvantage: Time-consuming and can damage cells.

Direct Microscopic Methods

• Advantage: Immediate results, can visualize cell morphology.

• Disadvantage: Can’t distinguish dead from live cells.

Turbidity

• Advantage: Quick and easy; provides an estimate.

• Disadvantage: Less accurate, influenced by non-cellular particulates.

Automatic Cell Counting

• Advantage: High-throughput and reliable.

• Disadvantage: Expensive equipment and potential calibration issues.

Flow Cytometry

• Advantage: High precision and ability to analyze multiple parameters.

• Disadvantage: Requires complex equipment and expensive reagents.