Microbiology Lab Flashcards
Gram (+) vs Gram (-)
Gram (+): retain purple iodine-dye complexes
Gram (-): don’t retain the complex when decolorized
Gram-non-reactive organisms stain very poorly or not at all (Mycobacterium tuberculosis, Leptospira interrogans, Borrelia burgdorferi)
Who developed Gram staining?
Hans Christian Gram
Why do Gram (+) bacteria retain the complex?
due to the peptidoglycan and teichoic acid cross links
Why do Gram (-) bacteria retain the complex?
because of the large amount of LPS in the cell wall.
Gram stain reagents
- crystal violet
- Gram’s iodine
- ethyl alcohol/acetone
- safranin/carbol fuscin
Gram staining:
What is the primary stain? What is the color stained?
Crystal violet - blue or bluish purple
It enhances reaction between cell wall and primary stain. It is a chemical that fixes a dye in or on a substance by combining with the dye to form an insoluble compound.
Mordant
Gram staining:
What is the counterstain? What is the color stained?
Carbolfuscin/safranin - pink
Gram staining:
What is the mordant?
Gram’s iodine
