History and Contributions in Microbiology

Major Figures and Their Contributions

• Antonie van Leeuwenhoek: First to observe and describe microorganisms ("animalcules") using a simple microscope.

• Ignaz Semmelweis: Introduced handwashing in medical practice, reducing puerperal fever in hospitals.

• Louis Pasteur: Disproved spontaneous generation, developed pasteurization, and contributed to vaccine development.

• Robert Koch: Established methods for isolating and identifying pathogens; formulated Koch's Postulates.

• Paul Ehrlich: Developed the concept of selective toxicity and the first chemotherapeutic agent (Salvarsan) for syphilis.

• Alexander Fleming: Discovered penicillin, the first antibiotic.

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 the disease when introduced into a healthy host.

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

Scientific Method and Hypothesis

Parts of the Scientific Method

• Observation: Gathering data and noticing phenomena.

• Hypothesis: A testable statement predicting an outcome.

• Experiment: Testing the hypothesis under controlled conditions.

• Analysis: Interpreting results.

• Conclusion: Accepting, rejecting, or modifying the hypothesis.

Law vs Theory

• Law: A statement describing consistent natural phenomena (e.g., Law of Gravity).

• Theory: A well-supported explanation of natural events (e.g., Theory of Evolution).

Correctly Written Hypothesis

• Should be clear, testable, and state the expected relationship between variables.

• Example: "If bacteria are exposed to penicillin, then their growth will be inhibited."

Basic Chemistry of Microbiology

Atoms and Their Properties

• Atomic Number: Number of protons in the nucleus.

• Atomic Mass: Sum of protons and neutrons. Calculation:

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Ions: Atoms or molecules with a net electric charge due to loss or gain of electrons.

• Energy Levels: Electrons occupy shells; first shell holds 2, second holds 8, third holds 8.

• Valence Electrons: Electrons in the outermost shell; determine bonding properties.

Chemical Bonds

• Nonpolar Covalent Bonds: Electrons shared equally (e.g., O2).

• Polar Covalent Bonds: Electrons shared unequally, creating partial charges (e.g., H2O).

• Ionic Bonds: Electrons transferred, forming charged ions (e.g., NaCl).

• Hydrogen Bonds: Weak attraction between a hydrogen atom and an electronegative atom (important in DNA and water).

Biological Molecules

Proteins

• Composition: Made of amino acids linked by peptide bonds.

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

• Structural Organization:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets.

  • Tertiary: 3D folding.

  • Quaternary: Multiple polypeptides joined.

Lipids

• Examples: Fats, oils, phospholipids, steroids.

• Saturated Fats: No double bonds; solid at room temperature.

• Unsaturated Fats: One or more double bonds; liquid at room temperature.

Carbohydrates

• Monosaccharides: Glucose, fructose.

• Disaccharides: Sucrose, lactose.

• Polysaccharides: Starch (plants, energy), glycogen (animals, energy), cellulose (plants, structure).

Nucleic Acids

• RNA Bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G).

• DNA Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

• Backbone: Sugar-phosphate.

• Nucleotide: Composed of a sugar, phosphate, and nitrogenous base.

Cell Structure and Function

Characteristics of Living Things

• Cellular organization, metabolism, growth, reproduction, response to stimuli, homeostasis.

Classification of Organisms

• Archaea: Prokaryotic, unique cell wall, extremophiles.

• Bacteria: Prokaryotic, peptidoglycan cell wall, diverse habitats.

• Fungi: Eukaryotic, chitin cell wall, decomposers.

• Protozoans: Eukaryotic, no cell wall, motile, single-celled.

• Algae: Eukaryotic, cellulose cell wall, photosynthetic.

Eukaryotic vs Prokaryotic Cells

• Similarities: Both have cell membranes, cytoplasm, genetic material.

• Differences:

  • Eukaryotes: Nucleus, membrane-bound organelles, larger size.

  • Prokaryotes: No nucleus, no organelles, smaller size.

• Motility Structures:

  • Pseudopods: Temporary extensions (e.g., amoeba).

  • Cilia: Short, numerous, for movement.

  • Flagella: Long, few, for movement.

• Cell Walls:

  • Bacteria: Peptidoglycan.

  • Fungi: Chitin.

  • Plants: Cellulose.

  • Archaea: Pseudomurein or other unique polymers.

• Single vs Multicellular:

  • Bacteria, Archaea: Single-celled.

  • Fungi, Algae: Can be multicellular.

Structures of Bacteria

• Plasmids: Small, circular DNA; transferred via conjugation.

• Inclusions: Storage granules for nutrients.

• Flagella: Motility; structure differs in Gram+ and Gram-.

• Fimbriae: Attachment to surfaces.

• Pili: DNA transfer (conjugation).

• Glycocalyx: Capsule (organized, protective) vs Slime Layer (loose, aids in adhesion).

• Cell Wall:

  • Gram+: Thick peptidoglycan, teichoic acids.

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

  • Fungi: Chitin.

  • Plants: Cellulose.

  • Archaea: Unique polymers.

• Membranes:

  • Gram+: Single membrane.

  • Gram-: Inner and outer membrane.

Bactericidal vs Bacteriostatic Antibiotics

• Bactericidal: Kill bacteria; preferred for severe infections.

• Bacteriostatic: Inhibit growth; rely on host immunity.

• Choice depends on: Cell wall and membrane structure (e.g., Gram- bacteria may be less susceptible to certain antibiotics).

Viruses

• Non-living, acellular, require host for replication, composed of nucleic acid and protein coat.

Archaea vs Bacteria vs Eukaryotes

• Archaea: Unique membrane lipids, no peptidoglycan, extremophiles.

• Bacteria: Peptidoglycan cell wall, diverse metabolism.

• Eukaryotes: Nucleus, organelles, complex structure.

Osmotic Terms

• Hypertonic: Higher solute concentration outside cell; cell shrinks.

• Isotonic: Equal solute concentration; no net movement.

• Hypotonic: Lower solute concentration outside; cell swells.

Dehydration Synthesis vs Hydrolysis

• Dehydration Synthesis: Joins molecules by removing water.

• Hydrolysis: Breaks molecules by adding water.

Microscopy and Staining

Parts of the Microscope

• Ocular lens (eyepiece), objective lenses (4x, 10x, 40x, 100x), stage, condenser, diaphragm, light source, coarse and fine focus.

Resolution, Magnification, and Contrast

• Resolution: Ability to distinguish two points as separate.

• Magnification: Enlargement of image; calculated as:

• Contrast: Difference in light intensity; enhanced by staining.

Calculating Magnification

• Ocular lens usually 10x.

• Objectives: 4x, 10x, 40x, 100x.

• Examples: 4x objective: 10x objective: 40x objective: 100x objective:

Oil Immersion

• Oil increases resolution by reducing light refraction at high magnification (100x objective).

Staining Techniques

• Simple Stain: Uses one dye to color cells.

• Acidic Stains: Negatively charged; stain background (e.g., nigrosin).

• Basic Stains: Positively charged; stain cells (e.g., crystal violet).

• Examples: Methylene blue, safranin.

Gram Stain Steps

1. Crystal violet (primary stain)

2. Iodine (mordant)

3. Alcohol (decolorizer)

4. Safranin (counterstain)

Definitions

• Pathogen: An organism that causes disease.

• Parasitism: Relationship where one organism benefits at the expense of another.