week 1

Comparison of Cell Sizes

  • Course Introduction
    • Scope of Microbiology
    • Cell Structure & Function
      đź“Ś Exam tip: Remember Janssen = compound microscope, Leeuwenhoek = first to see microbes

Historical Milestones in Microscopy

  1. Basic Concepts of Microscopy

    • The science of microbiology began with the invention of the microscope.
    • 1674 – Antonie van Leeuwenhoek: First to observe living microorganisms.
    • 1590 – Zaccharias & Hans Janssen: Built the first compound microscope (2 lenses).
    • Most common microscope used for studying biological functions.

  2. Types of Microscopes

    • Bright-Field Microscope
      • Used for visualization, identification, and studying function.
      • Background is dark, specimen is bright; often requires fixing and staining.
      • Magnifies objects not visible to the naked eye.
    • Dark-Field Microscope
      • Illuminates from the side, allowing observation of motility of living organisms.
      • Specimens appear dark on a bright background, ideal for unstained organisms.
    • Light Microscopes
      • Operate using visible light to study transparent, living cells.
      • Show good internal structures and surface details of the object.
    • Phase-Contrast Microscope
      • Produces high-contrast images of transparent specimens, ideal for microorganisms and thin tissue slices.
    • Fluorescence Microscope
      • Uses ultraviolet (UV) light; specimens fluoresce (glow).
    • Scanning Electron Microscope (SEM)
      • Produces 3D images; must use heavy metals for staining, requires dead specimens.
    • Transmission Electron Microscope (TEM)
      • Produces high-resolution 2D images; makes dense structures appear darker.
    • Scans Probe Microscopy (SPM)
      • Examines structures down to the atomic level, allows visualization of different layers.
    • Exam Favorites: Electron microscopes offer higher magnification and resolution.

Size and Comparison of Microorganisms

  • Bacteria: Approximately 1000 nm (1 µm)
    • Hundreds of viruses can fit on one bacterium.
  • Viruses: Typically 30–50 nm.
  • Red Blood Cells (RBC): About 7000 nm (7 µm).
  • Big Idea: Viruses are much smaller than bacteria and require different microscopy techniques for observation.

Microbiology Overview

  • Microbiology: The study of microorganisms – organisms too small to be seen with the naked eye.
    • Historical Context: Development linked to the understanding of disease causation and cellular processes.

Origins and Evolution of Microorganisms

  • Prokaryotes vs. Eukaryotes
    • Prokaryotes (No membrane-bound organelles): Came first, appeared ~2.2 billion years ago.
    • Includes Bacteria and Archaea.
    • Eukaryotes (Nucleus present): Have membrane-bound organelles; includes fungi, protists, and plant pathogens.
    • Other Infectious Agents
    • Viroids: Non-cellular, submicroscopic particles with RNA only.
    • Prions: Infectious misfolded proteins without nucleic acids.
    • Viruses: Composed of a protein coat and nucleic acid.

Germ Theory of Disease

  • Key Concepts
    • Biogenesis: Life comes only from preexisting life (disproved spontaneous generation).
    • Experimented by Francesco Redi (1668) and Louis Pasteur (1859).
    • Abiogenesis: Life arises from nonliving matter - the opposing theory.

Classification of Microorganisms

  • Three-Domain System (Woese-Fox System)
    • Divisions: Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species → Strain.
    • Taxonomy based on genetic rather than morphological similarities.
  • Binomial Nomenclature: Each organism has two names (Genus + species), where the genus is capitalized, and species is lowercase. Scientific names are italicized and underlined.

Microbial Relationships and Ecology

  • Normal Flora vs. Pathogens
    • Normal Flora: Microbes that reside in the human body without causing disease.
    • Pathogens: Organisms that cause diseases, categorized as parasites.
    • Symbiotic Relationships:
    • Parasitism: One organism benefits at the expense of the other.
    • Mutualism: Both organisms benefit.
    • Commensalism: One benefits, other not affected.
    • Synergism: Cooperation between two agents enhances effectiveness.

Microbial Applications

  • Applied Microbiology
    • Used in various fields such as agriculture, medicine, forensics, and bioremediation (natural way of reducing pollution).
  • Antibiotics and Pharmaceutical Agents
    • Produced by microorganisms (e.g., penicillin).
  • Food Production
    • Microorganisms involved in making yogurt, bread, wine, and beer.

Structure of Cells

  • Plasma Membrane: Fluid-mosaic model with phospholipid bilayer containing proteins, lipids, and carbohydrates.
    • Functions: Protection, transport of molecules, cell communication, response to stimuli, and structural support.
  • Extracellular Matrix: Surrounds animal cells, providing structural and functional support.
  • Cell Wall:
    • Provides shape and protection. Composition varies by organism (e.g., peptidoglycan in bacteria, cellulose in plants).
  • Cytoplasm: Site of most biochemical reactions; includes organelles and inclusions.

Cellular Structures and Functions

  • Key Organelles:
    • Nucleus: Control center containing DNA (in eukaryotes).
    • Ribosomes: Protein production (70S in prokaryotes; 80S in eukaryotes).
    • Mitochondria: Powerhouse of the cell, produce ATP, contain own DNA.
    • Chloroplasts: Site of photosynthesis in plants and algae.
    • Endoplasmic Reticulum & Golgi Apparatus: Involved in protein and lipid synthesis and modification.
    • Lysosomes: Digest waste and destroy microbes.
    • Vacuoles: Storage; contractile vacuoles remove excess water.

Biofilms

  • Formation Process: Microbial cells attaching to surfaces, forming dense layers.
    • New cells attach to the first layer, becoming resistant to antibiotics and disinfectants.
    • Cell Behavior: Changes as biofilm thickens; cells within become more complex and resistant to outside influences.

Koch’s Postulates (criteria for establishing a causative relationship between microbe and disease):

  1. The microbe must be present in all cases of the disease.
  2. The microbe must be isolated from the diseased host and grown in pure culture.
  3. When the cultured microorganism is introduced to a healthy host, the same disease must occur.
  4. The microbe must be re-isolated from the inoculated, diseased experimental host.