Microbiology

Question 1

Gram Positive

Answer 1

Thick layers of peptidoglycan
Bacteria produce exotoxins
Purple stain
Example Staphylococcus
Shape: spherical cocci

Question 2

Gram negative

Answer 2

Cell wall is composed of think Layers of peptidogylcan
Bacteria produce endotoxins
Pink stain
Example salmonella
Shape rod/ bacilli

Question 3

Staining

Answer 3

The process of adding a dye to a bacterial culture
• Gives cells colour and enables them to be seen by
improving the contrast.
• Achieved because of differences in charge
between the cells and the stain.

Question 4

Three types of staining procedures

Answer 4

Simple Staining
(shapes and
arrangements)
o Differential Staining (Gram
reactions)
o Special Staining
(Capsule, flagella, spor

Question 5

GRAM’S STAIN

Answer 5

Procedure
1. Crystal violet – 1 min – wash
2. Iodine – 1 min – wash
3. Acetone alcohol add drop by drop and watch out
colour comes out – wash immediately
4. Safarnine/dilute carbol fuchsin– 30secs. - wash.
5. Allow to dry
6. Examine under microscope.

Question 6

decolonized ( alcohol)

Answer 6

) Decolorizer:

Function: differentiating gram-positive from gram-negative bacteria.
It removes the crystal violet stain from gram-negative bacteria due to their thinner peptidoglycan layer and outer lipopolysaccharide membrane, which are more readily dissolved by the solvent. Gram-positive bacteria, with their thicker peptidoglycan layer, retain the crystal violet stain.

Question 7

Primary stain (crystal violet)

Answer 7

is responsible for initially staining all bacteria purple

Question 8

Mordant (grams iodine )

Answer 8

typically iodine, forms a complex with the primary stain, enhancing its affinity for the bacterial cells and preventing it from being easily washed out
Fixative causes the organisms to stick to the slide

Question 9

Differential stain

Answer 9

Differential staining is a procedure where more
than one dye is used to differentiate between
different types of microorganisms on a slide. This
type of staining helps to differentiate between cell
types and cell structures.

Question 10

Binary fission

Answer 10

Bacteria divide
Type of Asexual reproduction
Each cell divide into 2 equal size

Question 11

Stages of Bacterial Growth

Answer 11

Lag
Log
Stationary
Death

Question 12

Factors affecting Bacterial growth

Answer 12

Temperature
Ph
Availability of water
Atmospheric condition
Oxygen