MICROPARA 2

• Microbes


  Very tiny or microscopic organisms
• Micrometer (μm)


  Unit of measurement for microbes, 10^-6 m
• Nanometer (nm)


  Unit of measurement for microbes, 10^-9 m
• Angstrom (Å)


  0.1 nm
• Size of human red blood cells

  • 7 μm in diameter
• Relative sizes of microbes

  • 1 µm = 10^-6 m = 10^-3 mm
  • 1 nm = 10^-9 m = 10^-6 mm
  • 1000 nm = 1 µm
  • 0.001 µm = 1 nm
• Bacteria and protozoa size

  Usually expressed in micrometers (μm)
• Size of a typical spherical bacterium (coccus)

  • Approximately 1 μm in diameter
• Size of a typical rod-shaped bacterium (bacillus)


  • About 1 μm wide x 3 μm long
• Virus size


  Expressed in nanometers (nm), most human disease viruses range from 10 to 300 nm
• Size of some very large protozoa

  • Up to 2,000 μm (2 mm) in length
• Measuring microbe sizes in the lab

  1. Use ocular micrometer

  2. Calibrate with stage micrometer

  3. Determine distance between ocular micrometer marks for each objective lens

  4. Use ocular micrometer to measure lengths and widths
• Compound microscope


  Microscope with more than one magnifying lens
• Total magnification


  Objective lens × Ocular lens
• Resolution


  Ability of lenses to distinguish two points
• Microscope with 0.4 nm resolving power can distinguish points ≥ 0.4 nm
• Shorter wavelengths of light

  Provide greater resolution
• Refractive index


  Light-bending ability of a medium
• Immersion oil


  Used to prevent light from bending and missing the high-magnification lens
• Simple microscope


  Microscope with only one magnifying lens
• Magnifying glass


  • A simple microscope
• Compound light microscopes usually magnify objects about 1,000 times
• Photomicrograph


  Photograph taken through the lens system of a compound microscope
• Compound light microscope


  Uses visible light as the source of illumination
• Objects smaller than 0.225 μm cannot be seen using a compound light microscope
• Ocular lens


  Lens in the eyepiece with 10x magnifying power
• Objectives in a compound light microscope

  • 4x
  • 10x
  • 40x
  • 100x
• Oil immersion objective


  Total magnification of 1,000x, used to study bacteria
• Using the oil immersion objective


  1. Place drop of immersion oil between specimen and objective

  2. Reduces scattering of light and ensures light enters the lens
• Adjusting lighting on a compound microscope

  1. Open iris diaphragm in condenser

  2. Open field diaphragm

  3. Increase intensity of light bulb
• Resolving power


  Ability of lens system to distinguish between two adjacent objects
• Resolving power of compound light microscope is 1,000 times better than the unaided human eye
• Brightfield illumination


  Dark objects visible against a bright background
• Darkfield illumination


  Light objects visible against a dark background
• Use of darkfield microscopy


  • Diagnosis of primary syphilis
• Phase-contrast microscope


  Accentuates diffraction of light passing through specimen
• Fluorescence microscope


  Uses UV light, fluorescent substances absorb UV and emit visible light
• Differential interference contrast microscopy

  Accentuates diffraction of light passing through specimen, uses two beams of light
• Confocal microscopy


  Uses fluorochromes and a laser light to produce 3D images
• Atomic force microscopy (AFM)


  Enables observation of live microbes at high magnification and resolution under physiological conditions