Foundations of Microbiology

Prokaryotes vs. Eukaryotes

Microbiology distinguishes between prokaryotic and eukaryotic cells, which differ in structure and function.

• Prokaryotes: Cells lacking a nucleus and membrane-bound organelles (e.g., Bacteria, Archaea).

• Eukaryotes: Cells with a true nucleus and organelles (e.g., Fungi, Protozoa, Algae).

• Key differences: DNA location, cell wall composition, ribosome size, and complexity.

Cell-Based Organisms vs. Viruses

Viruses are acellular entities, while bacteria, archaea, and eukaryotes are cellular.

• Cell-based organisms: Capable of independent metabolism and reproduction.

• Viruses: Require host cells for replication; consist of genetic material (DNA/RNA) and a protein coat.

Key Scientists in Microbiology

Several scientists contributed foundational discoveries to microbiology.

• Antoni van Leeuwenhoek: First to observe microorganisms using a microscope.

• Francesco Redi: Disproved spontaneous generation with meat and maggot experiments.

• Louis Pasteur: Demonstrated biogenesis; developed pasteurization and vaccines.

• Robert Koch: Established Koch's postulates for linking microbes to disease.

• Ignaz Semmelweis: Advocated handwashing to prevent puerperal fever.

• Joseph Lister: Introduced antiseptic surgery.

• Edward Jenner: Developed the first vaccine (smallpox).

• Hans Christian Gram: Developed Gram staining technique.

Spontaneous Generation vs. Biogenesis

Early debates focused on whether life arises spontaneously or from existing life.

• Spontaneous generation: Life arises from non-living matter.

• Biogenesis: Life arises from pre-existing life.

• Key experiments: Redi's meat experiment, Pasteur's swan-neck flask experiment.

Germ Theory of Disease

The Germ Theory states that specific diseases are caused by specific microorganisms.

• Contributors: Pasteur, Koch, Lister.

• Applications: Disease prevention, development of vaccines, antiseptics.

Chemical Principles (Chapter 2)

Covalent and Ionic Bonds

Chemical bonds are essential for molecular structure and function.

• Covalent bonds: Atoms share electrons; strong and stable (e.g., H2O).

• Ionic bonds: Atoms transfer electrons; form ions (e.g., NaCl).

Hydrogen Bonds and Water Properties

Hydrogen bonds are weak attractions between polar molecules, crucial for water's properties.

• Hydrogen bond formation: Occurs between a hydrogen atom and an electronegative atom (O, N).

• Water properties: High cohesion, surface tension, solvent abilities.

Acids, Bases, and Buffers

Acids and bases affect pH; buffers stabilize pH in biological systems.

• Acid: Donates H+; lowers pH.

• Base: Accepts H+; raises pH.

• Buffer: Resists changes in pH.

• pH calculation:

Organic Compounds and Macromolecules

Organic molecules are carbon-based and form the basis of life.

• Types: Carbohydrates, lipids, proteins, nucleic acids.

• Phospholipids: Major component of cell membranes; amphipathic nature allows bilayer formation.

• Amphipathic: Molecules with both hydrophilic and hydrophobic regions.

Carbohydrates

Carbohydrates are energy sources and structural components.

• Monosaccharide: Single sugar unit (e.g., glucose).

• Disaccharide: Two sugar units (e.g., sucrose).

• Polysaccharide: Many sugar units (e.g., starch, cellulose).

Proteins

Proteins perform diverse functions and have hierarchical structure.

• Amino acid: Building block of proteins.

• Protein structure:

  1. Primary: Sequence of amino acids

  2. Secondary: Alpha helices and beta sheets

  3. Tertiary: 3D folding

  4. Quaternary: Multiple polypeptides

Microscopy (Chapter 4: 97-112)

Key Terms in Microscopy

Microscopy enables visualization of microorganisms.

• Electromagnetic spectrum: Range of wavelengths used in microscopy.

• Magnification: Increase in apparent size of an object.

• Resolution: Ability to distinguish two close objects as separate.

• Contrast: Difference in light intensity between specimen and background.

Compound Light Microscope Components

• Ocular lens

• Objective lenses

• Stage

• Light source

• Condenser

Total Magnification

• Calculation:

Refractive Index and Oil Immersion

• Refractive index: Measure of how light bends as it passes through substances.

• Oil immersion: Reduces light refraction, increases resolution at high magnification.

Types of Light Microscopes

• Compound light: General observation.

• Phase-contrast: Enhances contrast in transparent specimens.

• Fluorescence: Uses fluorescent dyes for specific labeling.

Staining Techniques

• Basic dyes: Positively charged; stain cell structures.

• Acidic dyes: Negatively charged; stain background.

• Differential stains: Distinguish cell types (e.g., Gram stain).

• Structural stains: Highlight specific structures (e.g., capsule, endospore).

Electron Microscopy

• Transmission Electron Microscope (TEM): Visualizes internal structures at high resolution.

• Scanning Electron Microscope (SEM): Visualizes surface structures in 3D.

Cell Structure and Function

Major Cell Components

• Cell wall: Provides shape and protection.

• Organelles: Specialized structures in eukaryotes.

• Glycocalyx: Outer coating for protection and adhesion.

• Membrane transport: Movement of substances across membranes.

• Ribosomes: Sites of protein synthesis.

• Flagella: Motility structures.

Bacterial Cell Shapes and Arrangements

• Cocci: Spherical

• Bacilli: Rod-shaped

• Spirilla: Spiral-shaped

Capsule vs. Slime Layer

• Capsule: Well-organized, firmly attached.

• Slime layer: Loosely attached, unorganized.

Pili and Fimbriae

• Pili: Used for conjugation (DNA transfer).

• Fimbriae: Used for attachment to surfaces.

Gram-Positive vs. Gram-Negative Cell Walls

• Gram-positive: Thick peptidoglycan, teichoic acids.

• Gram-negative: Thin peptidoglycan, outer membrane, lipopolysaccharide.

Mycoplasma and Mycobacterium

• Mycoplasma: Lacks cell wall; resistant to antibiotics targeting peptidoglycan.

• Mycobacterium: Waxy cell wall; acid-fast staining required.

Membrane Proteins and Transport

• Peripheral protein: Attached to membrane surface.

• Integral protein: Embedded within membrane.

• Selective permeability: Allows certain molecules to pass.

• Types of transport:

  • Simple diffusion

  • Facilitated diffusion

  • Osmosis

  • Active transport

  • Group translocation

Osmotic Pressure

• Hypotonic: Lower solute outside; cell swells.

• Hypertonic: Higher solute outside; cell shrinks.

• Isotonic: Equal solute; no net movement.

Plasmids and Endospores

• Plasmid: Small, circular DNA; confers advantages (e.g., antibiotic resistance).

• Endospore: Dormant, resistant structure; formed under stress.

• Sporulation: Process of endospore formation.

• Germination: Return to vegetative state.

Microbial Metabolism

Key Terms

• Catabolism: Breakdown of molecules; releases energy.

• Anabolism: Synthesis of molecules; requires energy.

• Catalyst: Substance that speeds up reactions.

• Activation energy: Energy required to start a reaction.

• Redox reaction: Transfer of electrons; includes oxidation and reduction.

• ATP: Main energy currency.

• Substrate-level phosphorylation: Direct transfer of phosphate to ADP.

• Oxidative phosphorylation: ATP generation via electron transport chain.

• Proton motive force: Drives ATP synthesis.

Endergonic vs. Exergonic Reactions

• Endergonic: Absorbs energy.

• Exergonic: Releases energy.

Enzymes, Cofactors, and Coenzymes

• Enzyme: Biological catalyst.

• Apoenzyme: Protein portion.

• Cofactor: Non-protein helper (metal ion).

• Coenzyme: Organic cofactor (e.g., NAD+).

• Lock and key model: Substrate fits precisely into enzyme active site.

Factors Affecting Enzyme Activity

• Temperature

• pH

• Saturation

• Competitive inhibitor

• Noncompetitive inhibitor

Aerobic Respiration Pathways

• Glycolysis

• Krebs cycle

• Electron transport chain

• ATP yield: Higher in aerobic than anaerobic respiration.

• Equation:

Aerobic vs. Anaerobic Respiration

• Aerobic: Uses oxygen as final electron acceptor.

• Anaerobic: Uses other molecules (e.g., nitrate, sulfate).

• Fermentation: Produces less ATP; end products include acids, alcohols, gases.

Catabolism vs. Anabolism

• Catabolism: Energy-releasing, breakdown.

• Anabolism: Energy-consuming, synthesis.

Microbial Growth (Chapter 6)

Growth Terms

• Psychrophile: Cold-loving

• Psychrotroph: Tolerates cold

• Mesophile: Moderate temperature

• Thermophile: Heat-loving

• Hyperthermophile: Extreme heat

• Acidophile: Acid-loving

• Neutrophile: Neutral pH

• Alkaliphile: Alkaline-loving

• Halophile: Salt-loving

Free Radicals and Enzymes

• Free radical: Highly reactive molecule; damages cells.

• Enzyme catalase: Breaks down hydrogen peroxide:

Oxygen Requirements

• Obligate aerobe: Requires oxygen.

• Obligate anaerobe: Killed by oxygen.

• Facultative anaerobe: Can use oxygen or not.

• Aerotolerant anaerobe: Tolerates oxygen, does not use it.

• Microaerophile: Requires low oxygen.

Clostridium perfringens

• Oxygen requirement: Obligate anaerobe.

• Pathogenicity: Causes gas gangrene; survives in low oxygen environments.

Biofilms and Quorum Sensing

• Biofilm: Community of microorganisms attached to a surface.

• Quorum sensing: Cell-to-cell communication regulating gene expression.

• Coordinated gene expression: Enables collective behaviors (e.g., virulence, resistance).

• Planktonic bacteria: Free-floating, not in biofilm.

Media Types

• Chemically defined media: Exact chemical composition known.

• Complex media: Contains extracts; composition varies.

• Selective media: Inhibits some microbes, allows others.

• Differential media: Distinguishes microbes by appearance.

Growth Phases

• Lag phase: Adaptation, no growth.

• Log phase: Exponential growth.

• Stationary phase: Growth rate equals death rate.

• Death phase: Decline in population.

Measuring Microbial Growth

• Plate counts with serial dilutions: Quantifies viable cells.

• Filtration: Captures microbes from liquids.

• Microscopic direct count: Counts cells under microscope.

• Turbidity: Measures cloudiness; correlates with cell density.