lecture 2 - introduction to microbiology pt 2
TRANSCRIPT
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Microscopes and Microscopy
Microscopic examination of microorganisms
makes use of either the light microscope or the
electron microscope
The compound light microscope is used for mostroutine examinations
The electron microscope is used for special
research purposes
All microscopes use lenses to magnify the image
of the cell
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Bright-Field
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Phase Contrast
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Fluorescence
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The Compound Light Microscope
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SEM
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TEM
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Scanning Transmission Electron
Microscope
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The Electron Microscope
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General Staining in Light
Microscopy
Various dyes used to increase contrast:
Methylene blue
Crystal violet
Safranin
These dyes are positively charged and
bind to negatively charged structures
such as DNA and various structures on
the cell surface
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Differential Staining in Light
Microscopy
The Gram stain is a very importantdifferential staining technique inmicrobiology
Bacterial cells can be split into two majorgroups based on gram staining:
Gram positive (stain purple)
Gram negative (pink-red) Bacterial cells are viewed with the x100
(oil immersion) lens in light microscopy
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The Gram Stain Add a drop of water to the slide
Add bacteria and smear Air dry
Heat fix
Add crystal violet for 1 min
Wash
Add iodine/potassium iodide for 1 min
Wash
Decolourise for 10-15 Sec Wash
Add safranin for 1 min
Wash
Blot dry
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Size of Microbial Cells
Bacterial size is generally measured inmicrometers (m)
1 m = 1 thousand times smaller than amillimeter (mm)
Typical bacterial cell like Escherichia coli(E. coli) measures 1 x 3 m
Typical eukaryotic cell ranges from 2
200 m Complex eukaryotes are made up of many
cells
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Overview of Cell Structure
Prokaryotes
Cytoplasmic
membrane
Cell wall Ribosomes
Genetic material
(DNA)
Inclusions (carbon,nitrogen, sulfur,
phosphorous)
Eukaryotes
Cytoplasmic
membrane
Cell wall Ribosomes
Nucleus
(chromosomes)
Various organelles vacuoles
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Nomenclature of Microbes
Full name is comprised of a genus and a
species name
First letter of genus name capitalised
Species name in common letters
Full name should be italicised