Microbiology and Parasitology Lab

• First microscope developed by Dutch lens grinders Hans and Zacharias Jansen


  1590
• Robert Hooke described the microscopic appearance of cork and used the term cell


  1667
• Anton van Leeuwenhoek was the first person to observe living cells under the microscope


  1675
• Microscopy


  • Used by scientists and health care professionals for diagnosis of infectious diseases, identification of microorganisms in environmental samples, and determination of the effect of pathogenic microbes on human cells
• Microscopic


  Objects too small to be seen with the unaided eye, needing to be magnified for the human eye to see them
• Light microscope


  • Uses visible light and two sets of lenses to produce a magnified image
  • Highest magnification possible is 1000X
• Magnification


  Making an object appear larger than it is
• Resolution


  The ability to see objects clearly enough to tell two distinct objects apart
• The limit of resolution of the human eye is about 0.1 mm, or 100 microns
• The limit of resolution of the light microscope is about 0.1 um, or 100 nm
• Biologists typically use microscopes to view all types of cells, including plant cells, animal cells, protozoa, algae, fungi and bacteria
• The nucleus and chloroplasts of eukaryotic cells can be seen, but smaller organelles and viruses are beyond the limit of resolution of the light microscope
• Metric units commonly used in Microbiology

  • Meter
  • Millimeter (mm)
  • Micrometer (micron, μm)
  • Nanometer (nm)
• Microscope use and care

  • Always carry with two hands
  • Use the assigned microscope
• Resolving power of microscopes ranges from the size of an atom to the height of a 5 year old child
• Cleaning the lenses


  Clean with lens cleaner (Windex) and lens tissue before and after use
• Report any problems with the microscope to your instructor immediately
• Cleaning oil off the microscope

  1. Oil must be cleaned off completely before returning the microscope to the cabinet

  2. If you accidentally get oil on the 40X objective, clean it immediately

  3. Microscopes must always be returned to the cabinet clean
• Putting away the microscope

  Microscopes should always be put away with a low power objective (4X or 10X) over the stage
• Always lift the microscope to reposition it-do not drag it across the surface of the table
• Total Magnification


  • The microscope has two sets of lenses that both contribute to the total magnification of the image
  • The ocular lenses magnify the image 10X
  • There are 4 different objective lenses, each with a different magnification
  • Total magnification = ocular magnification x objective magnification
• Objective lenses


  • Scanning
  • Low
  • High-dry
  • Oil immersion
• Determining the total magnification of an object with this microscope simply requires multiplying the objective magnification by 10
• Diversity of Cells


  • All cells have a plasma membrane, cytoplasm, and DNA
  • Some organisms are unicellular, others are multicellular
  • Cells that have a nucleus and organelles are eukaryotic, bacterial cells are prokaryotic
  • Some cells are photosynthetic, others take in organic molecules for energy
• Examining different cell types under the microscope

  1. Place slide on mechanical stage

  2. Center sample over light source

  3. Use coarse adjustment to bring stage up

  4. Rotate coarse adjustment knob to focus

  5. Use fine adjustment to improve clarity

  6. Increase magnification to 10X and 40X, refocusing each time

  7. Sketch what you are observing
• Preparing a wet mount

  1. Place 1-2 drops of pond water on slide

  2. Slowly lower coverslip to avoid air bubbles

  3. Place bacterial culture and methylene blue on slide, prepare wet mount
• Observe the prepared wet mount slides under the microscope