Gram Stain and Colonial Morphology Flashcards
What happens to a bacteria when it has an abundance of nutrients?
The bacteria will divide exponentially
What is a colony?
A group of thousands to billions of bacteria cell that have become visible.
What is another word for a colony?
Clone
What is a visible group of thousands/billions of bacteria cells called?
A colony or a clone
What is colonial morphology?
The characteristics of a colony
What are the characteristics of a colony known as?
Colonial morphology
Under what headings is the colonial morphology of a bacteria described.
(9)
Form
Margin
Elevation
Size
Surface
Consistency
Colour
Optical consistency
Odour
What does the gram stain differentiate bacteria into?
Gram positive and gram negative
Besides being gram positive or gram negative, what does a gram stain show us?
It shows us the cellular morphology of the organism
What does the gram reaction depend on?
It depends on the cell wall differences of peptidoglycan
What colour is peptidoglycan stained?
It is stained purple
What stains the peptidoglycan purple during a gram stain?
The crystal violet (CV) stains the peptidoglycan purple
Describe the amount of peptidoglycan in gram positive bacteria and what affect this has.
Gram-positive cell walls have a thick later of peptidoglycan, approximately 90% of the cell wall is peptidoglycan
How do gram positive bacteria resist decolourisation?
The cell wall of gram positive bacteria has numerous teichoic acid cross-linking which resists decolourisation
Do gram positive or gram negative bacteria have a cell wall made of 90% peptidoglycan?
Gram positive bacteria do
What percent of a gram negative bacteria’s cell wall is peptidoglycan?
About 10% of their cell wall is peptidoglycan
Why is iodine used after crystal violet>
2
The addition of iodine creates a large CV-I complex which is not easily dislodged from the thick peptidoglycan layers
It ensures the colour from the crystal violet will remain after decolourisation of gram positive bacteria
What is the decolourising agent used during a gram stain?
Ethanol
Why is ethanol added after the iodine?
Ethanol interacts with the lipids of the membranes of all bacteria.
The ethanol has one of two affects on the bacteria depending on whether it is gram positive or negative
What happens when ethanol is added to gram negative bacteria?
In gram negative bacteria the cell wall is dissolved by the ethanol, leaving the thin layer of peptidoglycan exposed and leaky
What happens when ethanol is added to gram positive bacteria?
In gram positive bacteria the highly cross-linked peptidoglycan dehydrates and traps the large CV-I complexes (purple colour remains)
What is added after the ethanol?
Carbol fuchsin is added
Why is carbol fuchsin added?
Carbol fuchsin gives a pink colour to the gram negative bacteria who’s peptidoglycan is now exposed
Give the order of the reagents used in a gram stain.
Crystal violet
Iodine
Ethanol
Carbol Fuchsin
How do you emulsify a colony for gram staining?
3
Using a sterile loop prepare a smear of the bacteria by placing 2-3 drops of water on a slide
Then using a sterile loop pick up a well defined colony
Emulsify the colony in the water to create a smear the size of a 1 euro coin
What should you do after you have emulsified a colony for gram staining?
(2)
Allow the smear to air dry, there should be a visible change
Then using a forceps pass the slide through a Bunsen flame to fix the bacteria
