Primary metric units used to measure microbes
Micrometers (µm) and nanometers (nm).
Most bacteria ≈ 1–10 µm
Viruses ≈ 20–300 nm
Metric system order
Kilo > Hecto > Deka > Base (meter, liter, gram) > Deci > Centi > Milli > Micro > Nano
Magnification
Increase in apparent size of an object using lenses.
Resolution
Ability to distinguish two closely spaced objects as separate; clarity of detail.
Contrast
Difference in light intensity between an object and its background; enhances visibility of structures.
Refraction
Bending of light as it passes between media of different densities (e.g., air to glass); enables lens-based magnification.
Microscopy
The science of using microscopes to view objects too small for the naked eye.
Wavelength Resolution Relationship
Resolution improves as wavelength decreases.
Shorter wavelengths → higher resolving power.
Wavelength range for visible light
Approximately 400–700 nm.
EMR Spectrum
Ranges from longest to shortest wavelength:
Radio → Microwave → Infrared → Visible → Ultraviolet → X-ray → Gamma rays.
Empty magnification
Magnification without increased resolution; image looks larger but blurry and lacks detail.
Factors that determine resolving power
Wavelength of light
Numerical aperture (NA) of the lens
Quality of optics
Relationship between contrast and staining
Staining increases contrast by coloring cells or structures, making them easier to distinguish from background.
Fluorescent vs Confocal Photography
Uses UV or blue light to excite fluorescent dyes
Produces brightly colored images on dark background
Confocal:
Uses lasers and optical sectioning
Creates high-resolution 3D images
Better depth and detail
TEM vs SEM
Transmission Electron Microscope (TEM):
Electrons pass through thin specimen
Provides internal detail (2D)
Very high resolution
Scanning Electron Microscope (SEM):
Electrons scan surface
Produces surface topography (3D)
Lower resolution than TEM
Difficulties in defining species of Microorganisms
Asexual reproduction → no biological species concept
High genetic diversity within species
Horizontal gene transfer
Phenotypic plasticity
Strains may differ significantly
Hierarch of taxa from general to specific
Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species
Binomial Nomenclature
Two-part Latin name: Genus + species.
Genus capitalized, species lowercase, both italicized (e.g., Escherichia coli).
5 kingdom system
Bacteria, Archaea, Eukarya.
3 kingdom system
Monera, Protista, Fungi, Plantae, Animalia.
modifications of Linaeus system
Addition of Kingdoms beyond Plantae and Animalia
Introduction of Domains above Kingdoms
Use of molecular/phylogenetic data (rRNA sequencing) for classification
