Introduction to Microbiology

Prokaryote vs. Eukaryote Cells

Cells are classified as either prokaryotes or eukaryotes based on structural and functional differences.

• Prokaryotes: Lack a nucleus and membrane-bound organelles; DNA is found in a nucleoid region. Examples: Bacteria, Archaea.

• Eukaryotes: Possess a nucleus and membrane-bound organelles. Examples: Fungi, Protozoa, Algae, Animals, Plants.

• Key Differences: Cell wall composition, ribosome size, complexity of internal structures.

Cell-Based Organisms vs. Viruses

Viruses differ fundamentally from cell-based organisms.

• Cell-Based Organisms: Composed of cells, capable of metabolism, growth, and reproduction independently.

• Viruses: Acellular, require host cells for replication, lack metabolic machinery.

• Example: Influenza virus vs. Escherichia coli (bacterium).

Key Scientists in Microbiology

Several scientists contributed to the foundation of microbiology.

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

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

• Louis Pasteur: Swan-neck flask experiments; disproved spontaneous generation for microbes; developed pasteurization.

• Robert Koch: Developed Koch's postulates; identified causative agents of disease.

• Ignaz Semmelweis: Promoted handwashing to prevent puerperal fever.

• Joseph Lister: Introduced antiseptic techniques in surgery.

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

• Hans Christian Gram: Developed Gram staining technique.

Spontaneous Generation vs. Biogenesis

Two theories debated the origin of 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 microorganisms cause disease.

• Contributions: Koch's postulates, Pasteur's work on fermentation and disease.

• Impact: Led to development of aseptic techniques and understanding of infectious diseases.

Chemical Principles

Covalent, Ionic, and Hydrogen Bonds

Chemical bonds are essential for molecular structure and function.

• Covalent Bonds: Atoms share electrons; strong and stable.

• Ionic Bonds: Atoms transfer electrons; form charged ions.

• Hydrogen Bonds: Weak attraction between hydrogen and electronegative atoms; important in water and biological molecules.

Properties of Water and Hydrogen Bonding

• Hydrogen Bonding: Gives water high cohesion, surface tension, and temperature stability.

• Example: Water's role as a solvent in biological systems.

pH, Acids, Bases, and Buffers

• pH: Measure of hydrogen ion concentration;

• Acid: Donates H+ ions; lowers pH.

• Base: Accepts H+ ions; raises pH.

• Buffer: Maintains stable pH by neutralizing acids and bases.

Organic Compounds and Elements

• Key Elements: Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur.

Lipids and Phospholipids

• Types of Lipids: Fats (triglycerides), phospholipids, steroids, waxes.

• Phospholipid Structure: Glycerol backbone, two fatty acid tails, phosphate group.

• Amphipathic: Molecule with both hydrophilic and hydrophobic regions; allows phospholipids to form cell membranes.

Carbohydrates

• Structure: Composed of monosaccharides (simple sugars).

• Function: Energy storage, structural support.

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

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

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

• Isomer: Molecules with same formula but different structure (e.g., glucose vs. fructose).

Amino Acids and Proteins

• Amino Acid: Building block of proteins; contains amino, carboxyl, and side chain.

• Protein Structure: Four levels: primary, secondary, tertiary, quaternary.

• Functions: Enzymes, structural, transport, signaling.

Nucleic Acids: DNA, RNA, and ATP

• DNA: Double-stranded, stores genetic information.

• RNA: Single-stranded, involved in protein synthesis.

• ATP: Energy currency of the cell; stores and transfers energy.

Anatomy of Bacterial Cells

Cell Structures: Eukaryote vs. Bacterial

• Cell Wall: Bacteria have peptidoglycan; eukaryotes may have cellulose or chitin.

• Organelles: Eukaryotes have membrane-bound organelles; bacteria do not.

• Glycocalyx: Protective layer; capsule (organized) or slime layer (loose).

• Membrane Transport: Selective permeability; various transport mechanisms.

• Ribosomes: Bacterial (70S), eukaryotic (80S).

• Flagella: Motility structures; differences in structure and arrangement.

Bacterial Shapes and Arrangements

• Shapes: Cocci (spherical), bacilli (rod-shaped), spirilla (spiral).

• Arrangements: Chains, clusters, pairs.

Capsule vs. Slime Layer

• Capsule: Organized, firmly attached; protects against phagocytosis.

• Slime Layer: Unorganized, loosely attached; aids in adhesion.

Fimbriae and Pili

• Fimbriae: Short, numerous; attachment to surfaces.

• Pili: Longer, fewer; conjugation (DNA transfer).

Gram Positive vs. Gram Negative Cell Walls

• Gram Positive: Thick peptidoglycan, teichoic acids.

• Gram Negative: Thin peptidoglycan, outer membrane with lipopolysaccharide.

Gram Stain Mechanism

• Gram Positive: Retain crystal violet, appear purple.

• Gram Negative: Lose crystal violet, take up safranin, appear pink.

Unique Bacterial Genera

• Mycoplasma: Lack cell wall.

• Mycobacterium: Waxy cell wall (mycolic acid).

Membrane Transport Terms

• Peripheral Protein: Attached to membrane surface.

• Integral Protein: Embedded within membrane.

• Selective Permeability: Allows certain molecules to pass.

• Hypotonic: Lower solute concentration outside cell.

• Hypertonic: Higher solute concentration outside cell.

• Isotonic: Equal solute concentration.

• Osmotic Pressure: Pressure exerted by solutes across membrane.

Types of Membrane Transport

• Simple Diffusion: Passive movement of small molecules.

• Facilitated Diffusion: Passive movement via proteins.

• Osmosis: Movement of water across membrane.

• Active Transport: Requires energy (ATP).

• Group Translocation: Substance chemically modified during transport.

Cell Wall and Osmotic Pressure

• Importance: Prevents cell lysis in hypotonic environments.

Internal Structures: Eukaryote vs. Bacterial

• Eukaryotes: Nucleus, mitochondria, ER, Golgi.

• Bacteria: Nucleoid, plasmids, ribosomes.

Plasmids

• Structure: Small, circular DNA.

• Function: Carry genes for antibiotic resistance, virulence.

Endospores

• Definition: Dormant, resistant structures.

• Formation: Sporulation triggered by stress.

• Purpose: Survival under harsh conditions.

• Germination: Return to vegetative state when conditions improve.

Microscopy, Staining, and Classification

Microscopy Terms

• Electromagnetic Spectrum: Range of wavelengths used in microscopy.

• Magnification: Enlargement of specimen image.

• Resolution: Ability to distinguish two points as separate.

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

Compound Light Microscope Components

• Eyepiece, objective lenses, stage, light source, condenser.

Total Magnification

• Calculation: Multiply eyepiece magnification by objective lens magnification.

• Example: 10x eyepiece × 40x objective = 400x total magnification.

Refractive Index and Oil Immersion

• Refractive Index: Measure of how light bends in a medium.

• Oil Immersion: Oil matches refractive index of glass, improves resolution at high magnification.

Types of Light Microscopes

• Compound Light: General observation.

• Phase-Contrast: Enhances contrast in unstained cells.

• Fluorescence: Uses fluorescent dyes; detects specific structures.

Staining Techniques

• Specimen Preparation: Fixation, staining.

• Basic Dyes: Positively charged; stain cell structures.

• Acidic Dyes: Negatively charged; stain background.

• Differential Stains: Distinguish cell types (e.g., Gram, acid-fast).

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

Purpose of Stains

• Gram Stain: Differentiates Gram positive and negative bacteria.

• Acid-Fast Stain: Identifies Mycobacterium.

• Capsule Stain: Detects protective capsules.

• Endospore Stain: Identifies endospores.

Electron Microscopy

• Transmission Electron Microscope (TEM): Views internal structures.

• Scanning Electron Microscope (SEM): Views surface structures.

Microbial Metabolism

Key Terms in Metabolism

• Metabolism: All chemical reactions in a cell.

• Catabolism: Breakdown of molecules; releases energy.

• Anabolism: Synthesis of molecules; requires energy.

• Catalyst: Speeds up reactions without being consumed.

• Activation Energy: Energy needed to start a reaction.

• Denaturation: Loss of protein structure/function.

• Redox Reaction: Transfer of electrons; reduction (gain), oxidation (loss).

• ATP: Adenosine triphosphate; energy carrier.

• Substrate Level Phosphorylation: Direct transfer of phosphate to ADP.

• Oxidative Phosphorylation: ATP synthesis via electron transport chain.

• Electron Transport Chain: Series of electron carriers; generates ATP.

• Proton Motive Force: Gradient of protons across membrane.

• Chemiosmosis: Movement of protons to generate ATP.

Endergonic vs. Exergonic Reactions

• Endergonic: Requires energy input.

• Exergonic: Releases energy.

Cofactor vs. Coenzyme

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

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

Enzyme-Substrate Complex

• Lock and Key: Enzyme's active site fits specific substrate.

Factors Affecting Enzyme Activity

• Temperature: High temp can denature enzymes.

• pH: Extreme pH can denature enzymes.

• Saturation: Maximum rate when all active sites are filled.

• Competitive Inhibitor: Competes with substrate for active site.

• Noncompetitive Inhibitor: Binds elsewhere, changes enzyme shape.

Glycolysis Types in Prokaryotes

• Embden-Meyerhof-Parnas (EMP): Produces ATP and NADH.

• Entner-Doudoroff (ED): Produces ATP and NADPH.

• Pentose Phosphate Pathway: Produces NADPH and pentoses.

Aerobic Respiration Pathways

• Glycolysis: Cytoplasm; produces ATP, NADH.

• Krebs Cycle: Mitochondria (eukaryotes), cytoplasm (prokaryotes); produces ATP, NADH, FADH2.

• Electron Transport Chain: Mitochondrial membrane (eukaryotes), plasma membrane (prokaryotes); produces most ATP.

• Oxygen Requirement: Final electron acceptor in aerobic respiration.

• End Products: CO2, H2O, ATP.

Overall Aerobic Respiration Equation

Aerobic vs. Anaerobic Respiration

• Aerobic: Uses oxygen as final electron acceptor.

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

Fermentation

• Pathway: Glycolysis followed by fermentation.

• Types: Alcoholic, lactic acid.

• Not Anaerobic Respiration: No electron transport chain.

Final Electron Acceptors

• Aerobic Respiration: Oxygen.

• Anaerobic Respiration: Nitrate, sulfate, etc.

• Fermentation: Organic molecules (e.g., pyruvate).

Metabolic Classification

• Photoautotroph: Light energy, CO2 carbon source.

• Photoheterotroph: Light energy, organic carbon source.

• Chemoautotroph: Chemical energy, CO2 carbon source.

• Chemoheterotroph: Chemical energy, organic carbon source.

Microbial Nutrition and Growth

Microbial Growth Terms

• Psychrophile: Grows at low temperatures (0-20°C).

• Psychrotroph: Grows at moderate cold (20-30°C).

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

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

• Hyperthermophile: Grows at very high temperatures (>80°C).

• Acidophile: Prefers acidic environments.

• Neutrophile: Prefers neutral pH.

• Alkaliphile: Prefers alkaline environments.

• Halophile: Prefers high salt concentrations.

Free Radicals and Enzymes

• Free Radical: Highly reactive molecule; damages cells.

• Source: Oxygen metabolism.

• Enzymes: Superoxide dismutase, catalase.

• Catalase Equation:

Oxygen Requirements of Microorganisms

• Obligate Aerobe: Requires oxygen.

• Obligate Anaerobe: Cannot tolerate oxygen.

• Facultative Anaerobe: Can grow with or without oxygen.

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

• Microaerophile: Requires low oxygen concentration.

Metabolism Types and Oxygen Requirements

• Obligate Aerobe: Aerobic respiration.

• Obligate Anaerobe: Anaerobic respiration, fermentation.

• Facultative Anaerobe: Aerobic respiration, anaerobic respiration, fermentation.

• Aerotolerant Anaerobe: Fermentation.

• Microaerophile: Aerobic respiration (low O2).

Clostridium perfringens and Oxygen Requirements

• Characterization: Obligate anaerobe.

• Importance: Causes illness in anaerobic environments (e.g., deep wounds).

Biofilms and Quorum Sensing

• Biofilm: Community of microorganisms attached to a surface.

• Quorum Sensing: Cell communication to coordinate gene expression.

• Coordinated Gene Expression: Enables group behaviors (e.g., virulence).

• Planktonic Bacteria: Free-floating, individual cells.

Biofilm Formation Steps

• Attachment

• Microcolony formation

• Maturation

• Dispersion

Media Types

• Chemically Defined Media: Exact composition known.

• Complex Media: Contains extracts; composition not fully known.

• Selective Media: Favors growth of specific microbes.

• Differential Media: Distinguishes between microbes based on reactions.

Pure Culture

• Definition: Population of cells derived from a single cell.

Growth Curves and Logarithms

• Phases: Lag, exponential (log), stationary, death.

• Logarithms: Used to plot exponential growth.

Methods to Plot Growth

• Plate Counts with Serial Dilutions: Quantifies viable cells.

• Filtration: Concentrates cells for counting.

• Microscopic Direct Count: Counts cells under microscope.

• Turbidity: Measures cloudiness; estimates cell density.