Microbiology 131: Study Notes on Microorganisms and Microscopy

Chapter 1 - Microorganisms

Introduction to Microorganisms

Microorganisms are microscopic living organisms that play essential roles in various biological and ecological processes. Understanding their functions helps prevent food spoilage, control disease spread, and utilize microbes for beneficial purposes.

• Definition: Microorganisms are organisms too small to be seen with the naked eye, including bacteria, archaea, fungi, algae, protozoa, and viruses.

• Importance:

  • Prevent food spoilage

  • Prevent and treat disease/epidemics

  • Decompose organic waste

  • Create oxygen (e.g., via photosynthesis)

  • Produce useful products (ethanol, vinegar, acetone)

  • Fermentation (e.g., yogurt, bread, alcohol)

  • Microbiome: all organisms living in and on the body

  • Help plants grow (nitrogen fixation)

  • Disbiosis: imbalance in microbiome can affect health

• Example: Lactobacillus species are used in yogurt fermentation and contribute to gut health.

Classification: The Three Domains

All cellular life is classified into three domains based on genetic and structural differences.

• Bacteria: Unicellular, peptidoglycan in cell walls, prokaryotic

• Archaea: Unicellular, no peptidoglycan in cell walls, often found in extreme environments, prokaryotic

• Eukarya: Multicellular or unicellular, includes animal parasites (helminths), algae (photosynthetic), fungi (energy from organic chemicals), protozoa (unicellular, various forms of movement)

• Viruses: Not part of the three domains; acellular, consist of DNA/RNA with a protein coat, can be pathogenic

Major Groups of Microbes

• Bacteria: Unicellular, prokaryotic, peptidoglycan cell walls

• Archaea: Unicellular, prokaryotic, no peptidoglycan

• Algae: Eukaryotic, photosynthetic, found in soil, water, and produce oxygen

• Fungi: Eukaryotic, obtain energy from organic chemicals, cell walls made of chitin

• Protozoa: Eukaryotic, unicellular, move by flagella, cilia, or pseudopods

• Viruses: Acellular, require host for replication

Historical Milestones in Microbiology

Key discoveries and figures have shaped the field of microbiology.

• 1665 - Robert Hooke: First microscope, cell theory (all living things made of cells)

• 1796 - Edward Jenner: Smallpox immunization from cowpox

• 1840s - Ignaz Semmelweis: Handwashing advocated to prevent disease

• 1854 - John Snow: Investigated cholera outbreak, linked to water source

• 1880 - Robert Koch: Established first microbiology lab

• 1928 - Alexander Fleming: Discovered Penicillium mold inhibits microbial growth

• 1940s - First antibiotic: Penicillin

Chapter 3 - Microscopy

Introduction to Microscopy

Microscopy is the use of microscopes to observe objects and organisms too small to be seen with the naked eye. It is fundamental in microbiology for studying cell structure and function.

• Optical Microscopy: Uses visible light and lenses to observe specimens

• Electron Microscopy: Uses beams of electrons for higher magnification and resolution

Types of Microscopy

• Compound Microscope: Uses multiple lenses (objective and ocular) to achieve magnification

• Brightfield Microscopy: Bright background, dark specimen; most common type

• Phase Contrast Microscopy: Enhances contrast to see internal cell structures

• Fluorescence Microscopy: Uses fluorescent dyes to stain specimens; allows visualization of specific cell structures

• Confocal Microscopy: Cells are stained, blue light excites a single plane, allows for 3D imaging

• Electron Microscopy: Uses electrons instead of light for much higher resolution

• Transmission Electron Microscopy (TEM): Beam of electrons passes through specimen; magnification up to 1,000,000x

• Scanning Electron Microscopy (SEM): Scans surface of specimen; magnification up to 100,000-500,000x

Key Concepts in Microscopy

• Resolution: Ability of a lens to distinguish two points as separate

  • Formula: $\text{Resolution} = \frac{0.61 \lambda}{n \sin \theta}$

  • Higher resolution allows for clearer images of small structures

• Refraction Index: Light bending ability of a medium

• Immersion Oil: Used in high magnification to prevent loss of light due to refraction

• Staining: Uses dyes to provide contrast and visualize cell structures

Scale and Measurement

• Microorganisms are measured in micrometers (μm) and nanometers (nm)

• Light microscopes can resolve objects down to ~200 nm

• Electron microscopes can resolve much smaller structures

Comparison of Microscopy Techniques

Type	Source	Resolution	Application
Brightfield	Visible light	~200 nm	General cell observation
Phase Contrast	Visible light	~200 nm	Internal cell structures
Fluorescence	UV light	~200 nm	Specific cell components
Confocal	Laser (blue light)	~200 nm	3D imaging
Transmission Electron (TEM)	Electron beam	~1-2 nm	Internal cell ultrastructure
Scanning Electron (SEM)	Electron beam	~10 nm	Surface structures

Example Application

• Fluorescence microscopy is used to detect specific proteins in cells by tagging them with fluorescent dyes.

• Electron microscopy allows visualization of viruses and detailed cell structures not visible with light microscopy.

Additional info: Some context and definitions were inferred to clarify fragmented notes and ensure completeness.