Module 1: Foundations of Microbiology – History, Chemical Principles, Microscopy, and Cell Anatomy

Scope and History of Microbiology

Definition and Importance of Microbiology

• Microbiology is the study of organisms and agents too small to be seen with the naked eye, including bacteria, viruses, fungi, protozoa, and some multicellular parasites.

• Microbes impact human society through their roles in disease, agriculture, medicine, drug production, food, ecology, and general health.

• Microbiology is divided into basic science (understanding life processes) and applied science (practical uses in health, industry, and environment).

Major Groups of Microorganisms

• Prokaryotes: Domains Archaea (Archaebacteria) and Bacteria (Eubacteria).

• Eukaryotes: Domain Eukarya, including protozoa, algae, fungi, and some animals (mainly worms and arthropods).

• Non-cellular life: Viruses.

Historical Milestones

• Microscope invented by Janssen & Lippershey (~1600).

• Robert Hooke (1665): Described cells in cork.

• Anton van Leeuwenhoek (1673–1683): First to observe protozoa and bacteria.

• Louis Pasteur (1850s–1860s): Demonstrated microbes cause fermentation and spoilage; developed pasteurization.

Spontaneous Generation vs. Biogenesis

• Spontaneous generation: The belief that life arises from nonliving matter.

• Key experiments:

  • Francesco Redi (1668): Showed maggots do not arise from covered meat.

  • John Needham (1745): Claimed spontaneous generation after heating broth.

  • Lazzaro Spallanzani (1765–1768): Showed boiling and sealing prevented growth.

  • Louis Pasteur (1861): Swan-neck flask experiment disproved spontaneous generation.

Germ Theory of Disease

• Proposed that microorganisms are the cause of many diseases.

• Key contributors:

  • Agostino Bassi (1835): Fungal cause of silkworm disease.

  • Joseph Lister (1860s): Introduced antiseptic surgery using phenol.

  • Robert Koch (1876–1882): Developed Koch's postulates to link microbes to disease; discovered causes of anthrax and tuberculosis.

Koch's Postulates

1. The suspected pathogen must be present in all cases of the disease and absent from healthy organisms.

2. The pathogen must be isolated and grown in pure culture.

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

4. The same pathogen must be re-isolated from the experimentally infected host.

Limitations: Some microbes cannot be cultured, and some diseases are not caused by a single organism.

Discovery of Viruses and Immunology

• Dmitri Ivanovsky (1892): Discovered viruses as filterable agents.

• Edward Jenner (1798): Developed smallpox vaccine using cowpox.

• Louis Pasteur: Developed vaccines for anthrax and rabies.

• Ilya Metchnikoff: Studied phagocytosis and inflammation.

Birth of Chemotherapy

• Paul Ehrlich: Searched for "magic bullet" drugs; developed Salvarsan for syphilis.

• Alexander Fleming (1928): Discovered penicillin.

Basic Chemical Principles

Atoms, Elements, and Compounds

• Atoms are composed of protons (+), neutrons (0), and electrons (–).

• Elements consist of only one type of atom; cannot be broken down further.

• Compounds are made of two or more types of atoms; can be molecular (covalent) or ionic.

• Mixtures are combinations of substances that can be separated physically.

Covalent and Ionic Bonds

• Covalent bonds: Atoms share electrons to fill outer shells (e.g., in carbohydrates, lipids, proteins).

• Ionic bonds: Formed by transfer of electrons, creating charged ions (e.g., NaCl).

• Oxidation: Loss of electrons; Reduction: Gain of electrons.

Water and Solutions

• Water is a polar solvent, dissolving polar and ionic compounds well.

• "Like dissolves like": Nonpolar molecules (e.g., fats) do not dissolve well in water.

• Biological molecules (sugars, proteins) often form aqueous solutions in cells and blood.

pH and Buffers

• pH measures the concentration of hydronium ions ($[H_3O^+]$) in solution.

• Pure water: $[H_3O^+] = [OH^-]$, pH = 7 (neutral).

• Acidic: $[H_3O^+] > [OH^-]$, pH < 7; Basic: $[H_3O^+] < [OH^-]$, pH > 7.

• Buffers resist changes in pH; important in culture media and biological systems.

Macromolecules

• Carbohydrates: Monosaccharides (simple sugars), disaccharides (two sugars), polysaccharides (many sugars; e.g., starch, glycogen, cellulose, peptidoglycan).

• Lipids: Fatty acids (saturated/unsaturated), triglycerides, phospholipids, sterols; key for energy storage and membranes.

• Proteins: Polymers of amino acids; structure levels include primary, secondary, tertiary, and quaternary.

• Nucleic acids: DNA and RNA; polymers of nucleotides (phosphate, pentose sugar, nitrogenous base).

• High-energy molecules: ATP (adenosine triphosphate) stores and transfers energy in cells.

Functional Anatomy of Prokaryotic and Eukaryotic Cells

Classification: Domains and Kingdoms

• Three Domains: Archaea, Bacteria, Eukarya.

• Six Kingdoms: Archaebacteria, Eubacteria, Protista, Fungi, Plantae, Animalia.

Prokaryotic Cell Morphology

• Cocci: Spherical (diplococci, streptococci, tetrads, sarcinae, staphylococci).

• Bacilli: Rod-shaped (diplobacilli, streptobacilli, coccobacilli).

• Spiral forms: Vibrio (curved rods), spirilla (rigid, corkscrew), spirochetes (flexible helix).

• Pleomorphic: Variable shape.

Cell Structures and Functions

• Plasma membrane: Phospholipid bilayer with proteins; permeability barrier, site for enzymes, energy storage.

• Cell wall: Peptidoglycan in bacteria; provides shape and protection.

• Gram-positive: Thick peptidoglycan layer.

• Gram-negative: Thin peptidoglycan, outer membrane with lipopolysaccharide (LPS).

• Archaea: Unique wall components (e.g., N-acetyltalosaminuronic acid).

• Flagella: Motility; "runs" and "tumbles" in response to stimuli (chemotaxis, phototaxis).

• Fimbriae and pili: Attachment and conjugation.

• Glycocalyx/capsule: Protection, adherence, biofilm formation.

• Nucleoid: Region containing circular DNA; may also have plasmids.

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

• Inclusions: Storage granules (e.g., poly-β-hydroxybutyric acid, glycogen, sulfur granules).

• Endospores: Dormant, resistant structures formed under stress (e.g., Bacillus, Clostridium).

Transport Across Membranes

• Passive transport: Simple diffusion (small, nonpolar molecules), facilitated diffusion (via proteins).

• Active transport: Requires energy (ATP or ion gradients) to move substances against concentration gradients.

• Osmosis: Movement of water across membranes; cells can be isotonic, hypotonic, or hypertonic relative to surroundings.

Table: Comparison of Gram-Positive and Gram-Negative Bacterial Cell Walls

Feature	Gram-Positive	Gram-Negative
Peptidoglycan Thickness	Thick (up to 40 layers)	Thin (1–2 layers)
Teichoic Acids	Present	Absent
Outer Membrane	Absent	Present (contains LPS)
Periplasmic Space	Small or absent	Large
Lipid Content	Low	High (due to outer membrane)
Sensitivity to Penicillin	High	Low

Microscopy

Units of Measurement

• Base unit: meter (m).

• Common units: millimeter (mm, $10^{-3}$ m), micrometer (µm, $10^{-6}$ m), nanometer (nm, $10^{-9}$ m), angstrom (Å, $10^{-10}$ m).

• Human eye resolution: ~100 µm; eukaryotic cells: ~50 µm; bacteria: 1–10 µm; viruses: 20–300 nm.

Compound Light Microscope Structure

• Key parts: ocular lens, objective lens, arm, base, stage, stage clip, fine/coarse focus knobs, iris diaphragm, field diaphragm, condenser, condenser height knob, light source.

• Oil immersion increases resolution by matching refractive index of glass and oil.

Resolution and Magnification

• Resolution: Ability to distinguish two points as separate; maximum for light microscope is ~0.2 µm.

• Magnification up to 1500x; higher magnification without increased resolution is "empty magnification."

• Numerical aperture (NA) indicates resolving power; higher NA = better resolution.

Types of Light Microscopy

• Brightfield: Standard illumination.

• Darkfield: Bright specimen on dark background; good for small features (e.g., flagella, spirochetes).

• Phase-contrast: Enhances contrast in unstained, living specimens by amplifying differences in refractive index.

• Differential interference (Nomarski): 3D-like images.

• Fluorescence: Detects light emitted from fluorochromes excited by specific wavelengths.

• Confocal: Uses lasers for optical sectioning and 3D reconstruction.

• Super-resolution: Advanced techniques for higher resolution beyond traditional limits.

Electron Microscopy

• Transmission Electron Microscopy (TEM): Thin sections stained with metals; magnification up to 100,000x.

• Scanning Electron Microscopy (SEM): Surface coated with metal; produces 3D images of surfaces.

Other Microscopy Techniques

• Scanning acoustic microscopy: Uses sound waves.

• Scanning tunneling microscopy and atomic force microscopy: Surface imaging at atomic resolution.

Measuring Microbes

• Ocular micrometer (in eyepiece) must be calibrated with a stage micrometer (known scale) for each objective lens.

• Once calibrated, can measure microbial size accurately at any magnification.

Laboratory Skills (Overview)

• Preparation of slant agar, deep agar, and broth subcultures.

• Colony transfer and isolation using streak or spread methods.

• Classification of colonies by form, elevation, pigmentation, and size.

• Classification of growth patterns in broth or on agar.

Additional info: This summary expands on brief points with academic context, definitions, and examples to provide a comprehensive, self-contained study guide for foundational microbiology topics.