Download Plate 14 - Staining Bacteria

Plate 14
Staining Bacteria
Why Stain?
• Most cells lack
color, so you must
stain them in order
to see them
Charges
• Positive molecules attract ________
negative molecules
• Positive molecules repel ________
positive molecules
• Negative molecules attract ________
positive molecules
negative molecules
• Negative molecules repel ________
Staining
• Positively charged dye molecules are
attracted to the negatively charged
cytoplasm
• Negatively charged dye molecules are
repelled by the negatively charged
cytoplasm
Simple Staining
• Only one color used
• Crystal violet dye is positively charged,
which is attracted by bacteria cytoplasm
Negative Staining
• A negatively charged dye is
used
• What effect will this have on
the bacteria cytoplasm?
– The cytoplasm will repel the
dye
– The background will be
stained, but not the bacteria
cell
– Looks like the night sky
Heat Fixing
• Cells need to be adhered
to the slide using heat
– Like an egg frying on a pan
• As proteins are heated,
they denature and stick to
the surface
• We will heat the slides for
2-3 minutes on a hot plate
Gram Staining
• Gram staining involves a
series of staining steps
used to differentiate
between 2 types of
bacteria cells
– Gram positive cells –
stain blue
– Gram negative cells –
stain red
Gram Staining Steps
1. Add crystal violet dye (wait 1 minute)
2. Wash slide with water
3. Add Gram’s iodine to lock in stain (wait 1
minute)
4. Add alcohol decolorizer to remove stain
from Gram negative cells
5. Add safranin dye (wait 1 minute)
6. Wash slide with water
Warm-Up
1.
2.
3.
4.
5.
What is the purpose of staining cells?
How do stains work?
What is the purpose of Gram staining?
What 2 dyes are used in Gram staining?
What are the steps of Gram staining?
Bacterial Cells
• Ideal age for Gram staining bacteria cells
is 24 hours
• Gram positive bacteria are susceptible to
certain antibiotics (like penicillin)
• Gram negative bacteria are susceptible to
other types of antibiotics