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Topic 10: Gram Staining
- The gram stain is a differential stain that allows you to classify bacteria as either gram positive or gram negative.
- Gram staining technique discovered by Hans Christian Gram in 1884.
- Steps
- Application of primary stain (crystal violet) - all bacteria are stained purple by this basic dye
- Application of mordant (gram’s iodine) - iodine combines with the crystal violet in the cell to form a crystal violet-iodine complex (CV-I)
- Application of decolorizing agent (ehtyl alcohol or ethyl alcohol-acetone) - primary is washed out of some bacteria while others are unaffected
- Application of secondary stain or counterstain (safranin) - basic dye stains the decolorized bacteria red
- The most important determining factor in the procedure is that bacteria differ in their rate of decolarization.
- Those that decolorize easily are gram-negative
- Those that decolorize slowly, and retain primary stain, are gram-positive
- CV-I complex cannot be washed out of gram-positive cells
- Decolorizing agent dissolves the outer lipopolysachharide layer and CV-I complex washes out through thin layer of peptidoglycan in gram-negative cells
- Gram stain is most consistent when done with young cultures of bacteria (less than 24 hours old)
- When bacteria die, their cell walls degrade and may not retain the primary stain → gives inaccurate results
- Gram staining is usually first step in identifying bacteria
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Explore Top NotesNoteStudied by 17 peopleNoteStudied by 12 peopleNoteStudied by 112 peopleNoteStudied by 21 peopleNoteStudied by 16 peopleNoteStudied by 26 people
4.15 Beethoven
NoteStudied by 17 peopleSoftball Study Guide
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NoteStudied by 21 peopleClimate Change - Exploring Earth Climate, Prevailing Winds, and How Heat Traps In Our Atmosphere
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