Lecture 2 - Introduction to Microbiology Pt 2

8/13/2019 Lecture 2 - Introduction to Microbiology Pt 2

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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

Lecture 2 - Introduction to Microbiology Pt 2

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