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Taxonomic Ranks

• Kingdom
• Division
• Class
• Order
• Family
• Genus
• Species

Light Microscope

• The most commonly used instrument for observing any cell in the light microscope, so named because visible light illuminates the object being studied.

Two Major Types of Stain (Based on ther

Taxonomic Ranks

• K - ingdom
• D - ivision
• C - lass
• O - rder
• F - amily
• G - enus
• S - pecies

Two Types of Stains (Based on their Affinity for Cell Components)

• 1.) Positive Stain - Have a strong attraction for 1 or more cell componenets.
• 2.) Negative Stain - Cannot penetrate a cell and thus make it highly visible by providing a contrasting dark background.

Stain Procedures

• 1) Simple Stain - Only a single dye is applied to a cell. Used to stain the whole cell or specific structures in the cell. Methylene blue (basic dye - which has a positive charge) is frequently applied to fixed bacteria to stain entire cells blue without staining the background material. Acidic dyes (having negative charges) which include eosin, fuchsin, and congo red.
• 2.) Differential Stains - Distinguish various kinds of bacteria because of difference in their surface structures.
• a.) Gram Stain - Is the most widely used staining procedure. It divides most cell bacteria into one of two groups; gram positive bacteria and gram-negative bacteria.
• Iodine - Forms dye-iodine complex *MORDANT*
• Alcohol - Gram-positive cells remain purple ; gram negative cells are completely *DECOLORIZED*
• Safranin - A *COUNTER STAIN* which is red dye. Gram positive cells remain purple; gram negative cells appear red.

Special Structures

• Capsular - The extra-cellular polymer forms a condensed, well defined layer closely surrounding the cell, it contributes to the invasiveness of pathogenic bacteria: Encapsulated cells are protected from Phagocytosis unless they are coated with anti-capsular antibody.
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