negative staining of capsules

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Last updated 4:33 AM on 7/16/26
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8 Terms

1
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do all bacteria have capsules?

no (differential stain)

  • encapsulated bacteria

  • non-encapsulated bacteria

2
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functions of capsules

  1. anti-phagocytic: limit ability of phagocyte to engulf bacteria

  2. attachment: to host tissue (cells) → promotes infection (sticky w/ polysaccharides)

3
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why identify capsules?

differentiate between different types of bacteria → identify bact → make proper dz diagnosis → give proper treatment → future prevention

4
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negative stain technique

= “indirect” staining (image not colored but everything else is)

5
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how do you know if a capsule is really present in the image?

  1. background: looks dark

  2. capsule: not stained! (clear halo)

  • not charged (non-ionic): b/c polysaccharides are uncharged

  • cannot pick-up charged dyes → will NOT STAIN

  1. bacterium: stains purple color (peptidoglycan (-) & dye chromophores (+))

6
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india ink

dark background; non-ionic dye → will NOT bind capsule

7
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crystal violet

stains bacterium inside the capsule

8
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heat fix?

NO! will destroy capsule (polysaccharides)