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

Scope and History of Microbiology

Introduction to Microbiology

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

• Microbes range in size from nanometer-scale viruses to nearly visible worm eggs.

• Microbiology is important for understanding disease, agriculture, medicine, ecology, and biotechnology.

Subfields of Microbiology

• Bacteriology: Study of bacteria

• Virology: Study of viruses

• Mycology: Study of fungi

• Parasitology: Study of protozoa and parasitic worms

• Immunology: Study of immune responses to microbes

Historical Contributions

• Anton van Leeuwenhoek: First to observe and describe microorganisms (1670s-1680s).

• Robert Hooke: Coined the term "cell" after observing cork (1665).

• Francesco Redi: Disproved spontaneous generation for larger organisms with controlled experiments (1668).

• John Needham: Supported spontaneous generation with flawed experiments (1745).

• Lazzaro Spallanzani: Improved Needham's experiments, showing boiling and sealing prevented microbial growth (1768).

• Louis Pasteur: Disproved spontaneous generation, developed pasteurization, and linked microbes to fermentation and spoilage (1850s-1860s).

• Joseph Lister: Introduced antiseptic techniques in surgery (1860s).

• Robert Koch: Developed Koch's postulates for linking microbes to disease; discovered causes of anthrax and tuberculosis.

• Edward Jenner: Developed the first vaccine (smallpox, 1798).

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

• Paul Ehrlich: Developed the first chemotherapeutic agent (Salvarsan for syphilis).

• Alexander Fleming: Discovered penicillin (1928).

Koch's Postulates

• Logical steps to establish a microbe as the cause of a disease:

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

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

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

  4. The same microbe 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

• Viruses discovered as agents passing through filters that retain bacteria (Ivanovsky, Beijerinck).

• Immunology began with Jenner's vaccination and Pasteur's artificial vaccines.

Chemical Principles in Microbiology

Atoms, Elements, and Compounds

• All matter is made of atoms (protons, neutrons, electrons).

• Elements consist of one type of atom; compounds contain two or more types of atoms.

• Compounds can be molecular (covalent) or ionic.

• Mixtures are physically combined substances that can be separated by physical means.

Covalent and Ionic Bonds

• Covalent bonds: Atoms share electrons to fill outer shells (e.g., water, proteins, DNA).

• Ionic bonds: Atoms transfer electrons, forming charged ions (e.g., NaCl).

• "Like dissolves like": Polar/charged molecules dissolve in water; nonpolar molecules (e.g., fats) do not.

Water and Solutions

• Water is a polar solvent, dissolving many biological molecules.

• Solutions consist of a solvent (e.g., water) and solutes (e.g., salts, sugars).

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 cellular processes.

Chemical Reactions and Energy

• Chemical reactions rearrange atoms and exchange energy.

• Exergonic reactions release energy; endergonic reactions require energy input.

Macromolecules in Cells

Carbohydrates

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose, lactose).

• Polysaccharides: Long chains (e.g., starch, glycogen, cellulose, chitin, peptidoglycan).

• Functions: Energy storage, structural support.

Lipids

• Composed of fatty acids and glycerol; include triglycerides, phospholipids, and sterols.

• Functions: Energy storage, membrane structure, hormones.

• Fatty acids can be saturated or unsaturated.

Proteins

• Polymers of amino acids (polypeptides).

• Levels of structure:

  1. Primary: Amino acid sequence

  2. Secondary: Alpha helices and beta sheets (hydrogen bonding)

  3. Tertiary: 3D folding (side chain interactions, disulfide bridges)

  4. Quaternary: Multiple polypeptide chains

• Functions: Enzymes, structural proteins, transport, signaling.

Nucleic Acids

• DNA and RNA are polymers of nucleotides (phosphate, pentose sugar, nitrogenous base).

• DNA: Double helix, deoxyribose sugar, bases A, T, G, C.

• RNA: Single strand, ribose sugar, bases A, U, G, C.

• Base pairing in DNA: A-T, G-C (hydrogen bonds).

High-Energy Molecules

• ATP (adenosine triphosphate): Main energy currency of the cell.

Functional Anatomy of Prokaryotic and Eukaryotic Cells

Classification: Domains and Kingdoms

• Three Domains: Archaea, Bacteria, Eukarya

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

• Viruses are not classified in the standard domains/kingdoms.

Prokaryotic Cell Morphology

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

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

• Spiral: Vibrio (curved rods), spirilla (rigid), spirochetes (flexible)

• Pleomorphic: Variable shape

Cell Structures and Functions

• Plasma (cytoplasmic) membrane: Permeability barrier, site for enzymes, energy storage (proton gradients).

• Cell wall: Provides shape and protection; made of peptidoglycan in bacteria.

• 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" for chemotaxis.

• Fimbriae and pili: Attachment and conjugation.

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

• Nucleoid: Region containing circular DNA.

• Plasmids: Small, extra-chromosomal DNA.

• 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 proton gradients) to move substances against concentration gradients.

• Osmosis: Diffusion of water across membranes; cells can be isotonic, hypotonic, or hypertonic relative to their environment.

Gram-Negative Cell Envelope

• Outer membrane: Contains LPS (lipid A is an endotoxin), porins for molecule passage.

• Periplasm: Space between outer and plasma membranes; contains enzymes and binding proteins.

Biofilms and Quorum Sensing

• Biofilms: Communities of microbes attached to surfaces, embedded in a self-produced matrix.

• Quorum sensing: Cell-to-cell communication to coordinate behavior based on population density.

• Medical relevance: Biofilms contribute to chronic infections and resistance to antibiotics.

Microscopy

Size Ranges and Measurement Units

• Base unit: meter (m)

• Common units: millimeter (mm), micrometer (µm), nanometer (nm), angstrom (Å)

• 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, focus knobs, iris diaphragm, condenser, 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; limited by wavelength of light (max ~0.2 µm for light microscopes).

• 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: Specimen appears bright against dark background; good for thin or small specimens (e.g., spirochetes).

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

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

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

• Confocal and two-photon microscopy: Improved resolution and depth for thick specimens.

Electron Microscopy

• Transmission Electron Microscopy (TEM): Thin sections, internal structures, magnification up to 100,000x.

• Scanning Electron Microscopy (SEM): Surface images, 3D appearance, specimens coated with metal.

Other Microscopy Techniques

• Scanning acoustic microscopy: Uses sound waves for imaging.

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

Staining Techniques

• Staining increases contrast; types include simple, differential (e.g., Gram stain), and special stains (e.g., for flagella, endospores).

Measuring Microbes

• Ocular micrometer (in eyepiece) calibrated with stage micrometer (known scale) at each objective.

• Allows accurate measurement of microbial size.

Laboratory Skills (Overview)

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

• Colony transfer and isolation (streak and spread methods).

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

• Classification of growth patterns in broth or on agar.

Table: Comparison of Prokaryotic and Eukaryotic Cell Structures

Feature	Prokaryotes	Eukaryotes
Nucleus	No (nucleoid region)	Yes (membrane-bound)
Cell Wall	Usually peptidoglycan (bacteria)	Cellulose (plants), chitin (fungi), absent in animals
Membrane Lipids	Ester-linked (bacteria), ether-linked (archaea)	Ester-linked, contain sterols (animals)
Ribosomes	70S	80S (cytoplasm), 70S (mitochondria/chloroplasts)
Organelles	Absent	Present (mitochondria, ER, Golgi, etc.)
Flagella	Simple, made of flagellin	Complex, 9+2 microtubule arrangement

Additional info: Table entries inferred and expanded for clarity.