Micro Lab 3: Differential Stains

what color are G+ bacteria

purple

what color are G- bacteria

pink

what color are acid-fast bacteria on an acid-fast stained slide

red/pink and blue

what color are non-acid-fast G+ and G- bacteria

acid-fast + → red/pink

acid-fast - → blue

what color are endospores in the staining method used on the demo slides

endospores: pink

cells: clear

what do bacterial capsules look like on the demo slides

have a halo around the cell

what dye is primary stain in the gram stain

crystal violet

why dye is the primary stain in the acid-fast stain

carbolfuschin

what is the mordant in the gram stain

iodine

what is the mordant in the acid-fast stain

steam

what is used at the decolorizer in the gram stain

alcohol

what color is the acid-fast stain

acid alcohol

what dye is the counterstain in the gram stain

saphranin

what is the counterstain in the acid-fast stain

methylene blue

what is the role of iodine in the gram stain procedure

causes the crystal violet to clump, this makes it get stuck in the gram positive wall

name a bacterial genus that produces endospores

Bacillus, Clostriduim

why/when do bacteria make endospores

• run out of food

• toxic conditions

• go dormant until conditions improve

name 2 diseases associated with endospore-forming bacteria

Tetanus, Botulism, Anthrax, Gas Gangrene

what advantage do bacteria with capsules have in infectious diseases

• allow for adherence

• allow for evasion of phagocytosis

• cover surface antigens & allow for evasion of antibodies

  • reduce drying out during transmission

name 2 diseases especially associated with encapsulated bacteria

Pneumonia, Meningitis, Anthrax

name 2 diseases caused by acid-fast bacteria

Tuberculosis, Leprosy

Your Gram-stain control contained G+ cocci and G– rods. What would the
stained slide have looked like if you forgot the counterstain, but did everything
else correctly?

• no Gram negative rods

• only G+ cocci

what would it look like if you forgot to decolorize

all cells would appear G+

What do you think would happen if you picked up the acid-alcohol from the
acid-fast stain box and used it to decolorize in the Gram stain instead of
alcohol?

• acid alcohol will decolorize Gram + and Gram -

• everything will appear G-