Chapter 1: A Brief History of Microbiology

What is Microbiology?

Microbiology is the scientific study of microorganisms, which are organisms too small to be seen with the naked eye. This field encompasses the biology, physiology, classification, and roles of bacteria, archaea, fungi, protozoa, algae, and small multicellular animals.

• Microorganisms include bacteria, archaea, fungi, protozoa, algae, and small multicellular animals.

• Microbiology explores their structure, function, genetics, and interactions with humans and the environment.

Key Scientists and Experiments

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

• Carolus Linnaeus: Developed the binomial nomenclature system for classifying organisms.

• Louis Pasteur: Disproved spontaneous generation (abiogenesis) with his swan-neck flask experiment; developed pasteurization.

• Robert Koch: Established Koch's postulates, linking specific microbes to specific diseases.

Six Categories of Microorganisms

• Bacteria: Prokaryotic, unicellular, diverse metabolism.

• Archaea: Prokaryotic, often extremophiles, distinct biochemistry from bacteria.

• Fungi: Eukaryotic, includes yeasts and molds, decomposers.

• Protozoa: Eukaryotic, unicellular, often motile.

• Algae: Eukaryotic, photosynthetic, aquatic.

• Small Multicellular Animals: Includes parasitic worms (helminths) and arthropods.

Major Questions in Microbiology

• Is spontaneous generation of microbial life possible?

• What causes fermentation?

• What causes disease?

• How can we prevent infection and disease?

Abiogenesis Debate and Pasteur’s Experiment

• Abiogenesis (spontaneous generation): The hypothesis that life arises from non-living matter.

• Pasteur’s Experiment: Used swan-necked flasks to show that boiled broth remained sterile unless exposed to airborne microbes, disproving abiogenesis.

• Pasteurization: Heating liquids to kill most bacteria and prevent spoilage.

Koch’s Postulates

• Set of criteria to establish a causative relationship between a microbe and a disease:

  1. The microorganism must be found in all cases of the disease.

  2. It must be isolated and grown in pure culture.

  3. The cultured microbe must cause disease when introduced into a healthy host.

  4. It must be re-isolated from the experimentally infected host.

Prevention of Infection and Disease

• Sanitation, sterilization, vaccination, and aseptic techniques are key methods.

Chapter 3: Cell Structure and Function

Basic Biomolecules and Chemistry of Life

All living organisms are composed of four major classes of biomolecules: carbohydrates, lipids, proteins, and nucleic acids. These molecules are essential for structure, function, and information storage.

• Carbohydrates: Energy storage and structural components.

• Lipids: Membrane structure, energy storage.

• Proteins: Enzymes, structural roles, signaling.

• Nucleic Acids: Genetic information (DNA, RNA).

What Constitutes Life?

• Growth, reproduction, responsiveness, metabolism, and cellular structure.

Prokaryotes vs. Eukaryotes

• Prokaryotes: No nucleus, simple structure (e.g., bacteria, archaea).

• Eukaryotes: Nucleus, membrane-bound organelles (e.g., fungi, protozoa, algae, animals, plants).

Bacterial Cell Structures

• Glycocalyx: Gelatinous outer layer; protects against desiccation and phagocytosis.

• Flagella: Motility structures; rotate to propel the cell.

• Fimbriae: Short, hair-like; attachment to surfaces.

• Pili: Longer than fimbriae; involved in conjugation (DNA transfer).

• Cell Wall: Provides shape and protection; Gram-positive (thick peptidoglycan) vs. Gram-negative (thin peptidoglycan, outer membrane).

• Cytoplasmic Membrane: Phospholipid bilayer; controls entry/exit of substances.

• Passive vs. Active Transport: Passive (diffusion, osmosis); active (requires energy, e.g., pumps).

• Osmotic States: Isotonic, hypotonic, hypertonic environments affect water movement.

• Cytosol: Liquid component of cytoplasm.

• Inclusions: Storage granules for nutrients.

• Ribosomes: Protein synthesis (70S in prokaryotes).

• Cytoskeleton: Structural support.

• Endospores: Dormant, resistant structures for survival.

Archaea vs. Bacteria (Structural Differences)

• Ribosomes: Different protein and RNA composition.

• Hami: Unique attachment structures in archaea.

• Cell wall composition: Archaea lack peptidoglycan.

Eukaryotic Structures and Processes Not Found in Bacteria

• Cell Walls: Present in fungi, algae, plants; composition differs (cellulose, chitin).

• Active Transport Types: Endocytosis, exocytosis.

• Flagella and Cilia: Complex, 9+2 microtubule arrangement.

• Internal Structures: Nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus.

Endosymbiotic Theory

• Proposes that mitochondria and chloroplasts originated from free-living prokaryotes engulfed by ancestral eukaryotic cells.

• Supported by similarities in DNA, ribosomes, and reproduction between these organelles and bacteria.

Chapter 4: Microscopy, Staining, and Classification

Units of Measurement

• Microbiology uses micrometers (μm, 10-6 m) and nanometers (nm, 10-9 m).

Principles of Microscopy

• Magnification: Increase in apparent size.

• Resolution: Ability to distinguish two points as separate.

• Contrast: Difference in intensity between an object and its background.

Types of Light Microscopes

• Bright-field: Standard, for stained specimens.

• Dark-field: Enhances contrast in unstained samples.

• Phase-contrast: Visualizes internal structures in living cells.

• Differential Interference Contrast (DIC): 3D-like images.

Fluorescent Microscopy

• Uses fluorescent dyes or proteins; specimens emit light upon excitation.

• Allows visualization of specific structures or molecules.

Electron Microscopy

• Transmission Electron Microscope (TEM): High-resolution images of internal structures.

• Scanning Electron Microscope (SEM): 3D images of surfaces.

Staining Techniques

• Purpose: Increases contrast and highlights structures.

• Acid Dyes: Negatively charged, stain background.

• Basic Dyes: Positively charged, stain cells.

• Simple Stains: Single dye, reveals shape and arrangement.

• Differential Stains: Multiple dyes, distinguishes cell types (e.g., Gram stain).

Taxonomy and Phylogeny

• Taxonomy: Science of classifying organisms.

• Phylogenetic Hierarchy: Evolutionary relationships among organisms.

• Identification uses morphology, biochemical tests, genetic analysis.

• Dichotomous Key: Stepwise tool for identification based on characteristics.

Chapters 5/6: Microbial Metabolism, Nutrition, and Growth

Metabolism: Catabolism vs. Anabolism

• Metabolism: All chemical reactions in a cell.

• Catabolism: Breakdown of molecules, releases energy.

• Anabolism: Synthesis of molecules, requires energy.

Enzymes: Function and Structure

• Biological catalysts; speed up reactions by lowering activation energy.

• Composed of proteins (sometimes with cofactors).

• Active site binds substrate; specificity determined by shape.

Microbial Growth Requirements

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

• Sources:

  • Carbon: Autotrophs (CO2), heterotrophs (organic compounds).

  • Energy: Phototrophs (light), chemotrophs (chemicals).

  • Electrons: Organotrophs (organic), lithotrophs (inorganic).

• Oxygen: Obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, aerotolerant anaerobes.

• Nitrogen: Required for amino acids, nucleotides.

• Growth Factors: Organic compounds required in small amounts (e.g., vitamins).

• Temperature: Affects enzyme activity; denaturation at extremes.

• pH: Most bacteria prefer neutral pH; acidophiles and alkaliphiles exist.

• Salinity: Halophiles tolerate high salt.

• Water: Required for metabolism; hydrostatic pressure affects deep-sea microbes.

Microbial Relationships and Biofilms

• Microbes interact as mutualists, commensals, or competitors.

• Biofilms: Communities of microbes attached to surfaces, embedded in extracellular matrix.

• Formation involves attachment, growth, and communication (quorum sensing).

• Biofilms confer protection and enhanced survival.

Culturing Microorganisms

• Aseptic Technique: Prevents contamination.

• Streak Plate: Isolates colonies.

• Pour/Spread Plate: Quantifies cells.

• Culture Media:

  • Agar: Solid medium; broth: liquid medium.

  • Defined: Exact composition known.

  • Complex: Contains unknown components (e.g., extracts).

  • Selective: Inhibits some microbes, allows others.

  • Differential: Distinguishes microbes by appearance.

  • Anaerobic: Supports growth without oxygen (e.g., anaerobic jar).

  • Transport: Maintains viability during transfer.

• Preservation: Refrigeration, freezing, lyophilization.

Binary Fission and Bacterial Growth

• Binary Fission: Asexual reproduction; cell divides into two identical cells.

• Generation Time: Time for population to double.

• Bacterial growth is exponential:

• Growth phases: Lag, log (exponential), stationary, death.

Measuring Microbial Growth

• Direct Methods: Microscopic counts, viable plate counts.

• Indirect Methods: Turbidity, metabolic activity, dry weight.

Chapters 9/10: Controlling Microbial Growth in the Environment and Body

Principles of Microbial Control

• Antiseptic: Reduces microbes on living tissue.

• Aseptic: Free of contamination.

• Degerming: Removal of microbes by mechanical means.

• Disinfection: Destroys most microbes on inanimate objects.

• Pasteurization: Reduces microbes in food/drink.

• Sanitization: Reduces microbes to safe levels.

• Sterilization: Destroys all microbes, including spores.

Choosing Control Methods

• Consider site, susceptibility of microbes, and environmental conditions.

Biosafety Levels (BSL)

Physical Methods of Control

• Heat:

  • Moist heat: Boiling, autoclaving, pasteurization, ultra-high temperature sterilization.

  • Dry heat: Incineration, hot air ovens.

• Refrigeration/Freezing: Slows or stops microbial growth.

• Desiccation/Lyophilization: Removes water to inhibit growth.

• Filtration: Removes microbes from liquids/air.

• Osmotic Pressure: High salt/sugar inhibits growth.

• Radiation:

  • Ionizing: X-rays, gamma rays (sterilization).

  • Nonionizing: UV light (surface disinfection).

Chemical Methods of Control

• Phenols/Phenolics: Disrupt membranes, denature proteins.

• Alcohols: Denature proteins, disrupt membranes.

• Halogens: Oxidize cell components (e.g., chlorine, iodine).

• Oxidizing Agents: Peroxides, ozone.

• Surfactants: Soaps, detergents; disrupt membranes.

• Heavy Metals: Inactivate proteins (e.g., silver, mercury).

• Aldehydes: Cross-link proteins and nucleic acids.

• Gaseous Agents: Sterilize in closed chambers (e.g., ethylene oxide).

• Enzymes: Digest cell walls or membranes.

• Antimicrobial Drugs: Target specific microbial processes.

Antibiotics, Semisynthetic, and Synthetic Drugs

• Antibiotics: Naturally produced by microbes.

• Semisynthetic: Chemically modified antibiotics.

• Synthetic: Completely synthesized in the lab.

Mechanisms of Antimicrobial Action

• Selective Toxicity: Targets microbial structures/processes not found in host.

• Inhibition of Cell Wall Synthesis: E.g., penicillins (bacteria), echinocandins (fungi).

• Inhibition of Protein Synthesis: Targets prokaryotic ribosomes or tRNA charging.

• Disruption of Cytoplasmic Membranes: E.g., polymyxins, antifungals.

• Inhibition of Metabolic Pathways: E.g., sulfonamides.

• Inhibition of Nucleic Acid Synthesis: E.g., quinolones, rifampin.

• Prevention of Virus Attachment/Entry/Uncoating: E.g., antiviral drugs.

Clinical Considerations in Antimicrobial Use

• Spectrum of Action: Broad vs. narrow spectrum.

• Effectiveness:

  • Diffusion susceptibility test (Kirby-Bauer disk diffusion).

  • Minimum Inhibitory Concentration (MIC): Lowest concentration preventing growth.

  • Minimum Bactericidal Concentration (MBC): Lowest concentration killing bacteria.

• Routes of Administration: Oral, topical, intravenous, intramuscular.

• Safety and Side Effects: Toxicity, allergies, disruption of normal microbiota.

Development and Mechanisms of Resistance

• Resistance: Microbes evolve to withstand drugs.

• Mechanisms: Mutation, acquisition of R plasmids, persister cells.

• Seven general mechanisms: Enzyme production, target modification, decreased permeability, efflux pumps, metabolic pathway changes, biofilm formation, protection of target site.

• Threat Levels: Urgent, serious, concerning (CDC classification).

• Multiple and Cross Resistance: Resistance to multiple drugs or similar drugs.

• Retarding Resistance: Use drugs appropriately, combination therapy, limit use, develop new drugs.