1) Micro Bio Lab Practical (Capsule & Gram stain)

What is the purpose of the capsule stain?

Differential stain; differentiate between capsule producing cells & unencapsulated cells

What are the functions of a capsule?

1) Acts as adherence factor

2) Protects bacteria from dehydration, nutrient loss, and phagocytosis

What is the capsule made of in the capsule stain?

Mucoid polysaccharide or polypeptide

What is the cell stained with in the capsule stain and what color is it?

Stained w/ basic stain safranin, pinkish red

What is the background stained with in the capsule stain and what color is it?

Stained w/ acidic (-) stain, congo red

What does the clear area in a capsule stain represent?

The capsule

What is an example of a capsule stained bacteria?

Klebsiella pneumoniae

What is the purpose of the gram stain?

Differential stain; differentiate gram (+) from gram (-) bacteria

Why is the gram stain important?

Used to select appropriate antibiotic

What dyes are used in the gram stain?

Crystal Violet

Safranin

What color is gram (+) in gram stain?

Purple

What color is gram (-) in gram stain?

Pinkish red

Why do gram (+) retain crystal violet?

Thick peptidoglycan layer

Why don’t gram (-) retain crystal violet?

Thin peptidoglycan layer

Needle or loop to transfer bacteria in gram stain?

Needle

Why heat fix slides?

1) Kill bacteria

2) make bacteria stick to slide

3) Proteins denature & coagulate

What is the gram stain procedure?

1) Crystal violet, rinse w/ DI

2) Iodine (mordant), rinse w/ DI

3) Decolorization until clear

4) Safranin (counterstain)

What is the purpose of iodine in gram stain?

To form crystal violet-iodine complex in gram (+)

Gram stain bacteria examples

Gram (-) rods = E. coli

Gram (+) cocci = Staphylococcus aureus