Admin Table of Contents
Why crystal violet inhibit the Gram positive bacteria?
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.
Why does MacConkey agar inhibit Gram-positive?
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.
How bile salts inhibit Gram positive bacteria?
Here, we report the discovery that bile salts affect bacterial growth by causing widespread unfolding and aggregation of cytosolic proteins in bacteria, while simultaneously triggering a prooxidizing shift in the cellular ratio of reduced to oxidized glutathione.
What is the role of the crystal violet and bile salts in MacConkey 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.
How does crystal violet inhibit growth?
Crystal violet has an antibacterial action against Escherichia coli, Staphylococcus aureus, Streptococcus faecalis and Bacillus subtilis. The effect of the dye, measured as minimum inhibitory concentration or retardation of growth, increases as the pH rises from 6 to 8. Gram-negative organisms, such as E.
What is the purpose of bile salts in the MacConkey agar?
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.
What is the purpose of bile salts in the MacConkey Agar?
What is the role of bile salts in he Agar?
Bile salts render the medium selective, inhibiting Gram positive organisms and reducing growth of some gram-negative organisms other than Salmonella and Shigella.
Why are crystal violet agar and 7.5% sodium chloride agar considered selective media?
Why are crystal violet agar and 7.5% sodium chloride agar considered selective media? They are used to select or isolate specific bacteria. Gram-positive organisms are very sensitive to the basic dye in CV. NaCL produces an osmotic environment not conductive for any organism besides halophiles.
What is the purpose of crystal violet?
In the Gram staining method, crystal violet is used to differentiate between Gram Positive and Gram Negative bacteria.