Quiz 2 Flashcards
(53 cards)
What is the purpose of the gram stain?
The gram stain helps us differentiate between gram + and gram - bacteria. It is the first step in identifying an unknown bacteria
What is the first step in the gram stain procedure? What is happening chemically?
The first step involves the primary stain, which is done with crystal violet. The crystal violet dyes all forms of bacteria because it is a cationic substance reacting with an anionic exterior of bacteria.
What is the second step in the gram stain procedure? What is happening chemically?
The second step is the mordant and it is iodine. The iodine creates a crystal complex which allows the crystal violet to stick properly to the cell wall
What is the third step in the gram stain procedure? What is happening chemically?
The third step is decolorize and it is done with ethanol. The alcohol does not allow gram - to retain crystal violet and will dissolve the color. In gram + nothing will happen
What is the fourth step in the gram stain procedure? What is happening chemically?
The fourth step involves a counterstain and it is done with safranin. Since it is lighter than violet, it will not affect the gram + bacteria that have crystal violet. Since gram - bacteria are decolorized from previous stain, it will stain them pink/red
What is the difference between gram +and gram - bacterial cell walls?
Gram + have an inner cell membrane and a thick peptidoglycan layer
Gram - have an inner cell membrane, thin peptidoglycan layer, and an outer cell membrane
What would happen if iodine was left out of the procedure?
Since iodine allows crystal violet to bind to cells, skipping this step will not allow us to see a clear difference between gram + and gram -
What would happen if ethanol was left out of the procedure?
Since alcohol usually dissolves lipids (outer layer of gram -), skipping this step will not allow gram - bacteria to turn pink since they will not be decolorized
What would happen if safranin was left out?
Since safranin helps stain gram - cells, skipping this step will not allow us to see them. We would only observe gram + bacteria
What happens if we perform a gram stain on cultures that are old?
It could give us false results and we could see a mixture of pink and purple for all types of bacteria (regardless of gram -/+
What is the purpose of the acid fast stain?
The Acid-fast stain is used to identify Mycobacterium species based on the detection of the mycolic acid layer
What is the main pathogen associated with the presence of mycolic acid? What disease does it cause in us?
Mycobacterium Tuberculosis, causes TB in us
What is the first step in acid fast staining?
We first stain with Carbolfushion (KF) for 4 minutes
What is the second step in acid fast staining?
The second step is Decolorizer, which is Acid Alcohol for up to 30 seconds.
What is the third step in acid fast staining?
Counterstaining with Methylene blue for 30 seconds
What is the interpretation of acid fast stain?
Dark red/pink rods: positive…mycolic acid present
Blue rods: negative… no mycolic acid present
What is an endospore?
It is a specialized cell structure that keeps bacteria alive during extreme environmental conditions
What substances do we use for an endospore stain?
Malachite green and Safranin
What is an example of capsules (aka slime layers)?
Bio films
What is nosocomial?
A hospital acquired infection
What is a vegetative state for bacteria?
Basically, bacteria without spores. When a bacteria becomes “active” again (feeding, reproducing, excreting, etc), after being an endospore, we can describe it as a vegetative state.
What is a bacterial capsule?
A bacterial capsule can be referred to as glycocalyx. Within glycocalyx, we have different types of capsules that benefit bacteria in many ways. In most cases, a capsule will help bacteria be protected from an outside environment, thus making it a virulence factor.
Why is capsule staining also called negative staining?
Because the capsule itself is not stained. Instead the background and bacteria are stained but the capsule is left free from stain.
What substances do we use to stain capsules?
We use congo red and maneval’s stain
