Table of Contents
- 1 What is the purpose of crystal violet agar?
- 2 What Gram positive bacteria can grow on MacConkey Agar?
- 3 What is the purpose of crystal violet in the MacConkey agar medium?
- 4 Is crystal violet a reagent?
- 5 How does crystal violet dye work on MAC agar?
- 6 What does crystal violet do to Gram positive bacteria?
What is the purpose of crystal violet agar?
Crystal Violet Erythromycin Agar (CVE) is an enriched, selective, and differential medium used for the isolation and presumptive identification of Fusobacterium nucleatum.
Why does crystal violet act as a selective agent against Gram positive bacteria in the MacConkey agar test?
Principle of MacConkey Agar Lactose monohydrate is the fermentable source of carbohydrate. The selective action of this medium is attributed to crystal violet and bile salts, which are inhibitory to most species of gram-positive bacteria. Sodium chloride maintains the osmotic balance in the medium.
What would happen if the crystal violet inhibitor was removed from the MacConkey Agar?
How would removing crystal violet from MacConkey Agar alter the sensitivity and specificity of the medium? It would inhibit the growth of gram positive bacteria because this test is used to differentiate the gram positive bacteria and enterobacteria.
What Gram positive bacteria can grow on MacConkey Agar?
Colony Morphology of some common bacteria on MacConkey Agar
| Organism | Type |
|---|---|
| Salmonella spp | Non-Lactose Fermenter |
| Pseudomonas spp | Non-Lactose Fermenter |
| Yersinia spp | Non-Lactose Fermenter |
| Gram positive bacteria |
What step is crystal violet?
The organisms that do not take up primary stain appear red under a microscope and are Gram-negative organisms. The first step in gram staining is the use of crystal violet dye for the slide’s initial staining.
What are three uses for crystal violet?
What are 3 possible uses for Crystal Violet? Simple Stain. Gram Stain. Anti-fungal/anti-gram (+) bacteria.
What is the purpose of crystal violet in the MacConkey agar medium?
Crystal violet dye and bile salts halt the growth of gram-positive bacteria. This allows only gram-negative species to form colonies on MAC agar. [2] MacConkey agar contains the essential nutrients required for microorganism growth.
What are the purposes of crystal violet and bile salts in MacConkey agar are these ingredients selective or differential?
MacConkey Agar (MAC) is a selective and differential medium designed to isolate and differentiate enterics based on their ability to ferment lactose. Bile salts and crystal violet inhibit the growth of Gram positive organisms. Lactose provides a source of fermentable carbohydrate, allowing for differentiation.
How does crystal violet inhibit Gram positive?
A decolorizer such as ethyl alcohol or acetone is added to the sample, which dehydrates the peptidoglycan layer, shrinking and tightening it. The large crystal violet-iodine complex is not able to penetrate this tightened peptidoglycan layer, and is thus trapped in the cell in Gram positive bacteria.
Is crystal violet a reagent?
Crystal violet, in a hydrobromic acid medium, forms a colored chelate with thallium. As such it can be used as a thallium sensitive reagent.
How do you use crystal violet?
Add the primary stain (crystal violet) to the sample/slide and incubate for 1 minute. Rinse slide with a gentle stream of water for a maximum of 5 seconds to remove unbound crystal violet. Add Gram’s iodine for 1 minute- this is a mordant, or an agent that fixes the crystal violet to the bacterial cell wall.
How is crystal violet made?
Dissolve 2 g crystal violet in 20 ml of 95% ethyl alcohol. Dissolve 0.8 g ammonium oxalate monohydrate in 80 ml deionized water. Mix the crystal violet and ammonium oxalate monohydrate solutions to make the crystal violet stain.
How does crystal violet dye work on MAC agar?
Crystal violet dye and bile salts halt the growth of gram-positive bacteria. This allows only gram-negative species to form colonies on MAC agar. MacConkey agar contains the essential nutrients required for microorganism growth. Additional key components include crystal violet dye, bile salts, lactose, and neutral red (a pH indicator).
What makes MacConkey agar a selective medium?
(3, 4) MacConkey’s Agar is a selective medium. It prevents the growth of gram-positive bacteria because of the presence of bile salts and crystal violet. Only gram-negative bacteria has the ability to thrive on MacConkey agar.
What are the components of the MacConkey medium?
Key components of the MacConkey medium include crystal violet dye, bile salts, lactose, and neutral red (pH indicator). Crystal violet dye and bile salts halt the growth of gram-positive bacteria. This allows only gram-negative species to form colonies on MAC agar.
What does crystal violet do to Gram positive bacteria?
What crystal violet does is it deeply penetrates the cell wall of gram positive bacteria. It restraints the growth of gram positive bacteria, making the MacConkey agar a selecting medium. If you want to find out if the bacteria is gram positive, see to it that you added a crystal violet in the agar formula.