Please answer 5,6, and 7. Compare the recipes of Nutrient Agar and XLD Agar. If
ID: 165488 • Letter: P
Question
Please answer 5,6, and 7. Compare the recipes of Nutrient Agar and XLD Agar. If an organism can grow on both media, on which would you expect it to grow better? Why? XLD is a selective medium. Is it also a defined or an undefined medium? Why is that formation desirable? What would be the likely consequence of: incubating the medium for 48 hours? not adding desoxycholate? not adding sucrose and lactose? not adding lysine? not adding ferric ammonium citrate? How would each of the changes in question #5 affect the sensitivity and specificity of the medium? Shigella and Providence species virtually never ferment xylose, sucrose or lactose. Since the medium was designed to directly identify these organisms, why were three unusable carbohydrates included when only one would seem to accomplish the goal?Explanation / Answer
5 & 6
CONSEQUENCE OF NOT ADDING: Gram-positive microorganisms can’t be inhibited in the medium
CONSEQUENCE OF NOT ADDING: sugar fermentation will not occur, Thus the pH will not be lowered and the indicator will not change its color in the medium
CONSEQUENCE OF NOT ADDING; H2S production will not be visualized in the medium.
CONSEQUENCE OF NOT ADDING: No observable differentiation between Salmonella and other pathogens .
Thus these changes will yield
7. Here Xylose, sucrose and lactose are the fermentable sugars. Xylose is fermented by almost all the enteric bacteria except Shigellae, which enable the differentiation of Shigellae from Salmonellae. After the exhaustion of xylose by salmonella, the lysine is attacked via the enzyme lysine decarboxylase, and change the pH to alkaline which mimics the Shigella reaction.
To prevent this reaction, lactose and sucrose are added to produce acid in excess.
Thus lactose and sucrose helps in differention of bacteria between Salmonellae and Shigellae
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.