5-18 Urease

7. Ideally, we should have done this exercise with both urea broth and urea agar, and we should have continued to watch for positive results for up to 6 days. Since we did not do that, what problems may we have in making correct predictions and conclusions?

One may conclude that the organisms in a negative resulting media does not produce urease

8. Suppose you ran this test with Providencia stuartii, but it took 48 hours to turn pink. Do you think this is a false result? If so, is it a false positive or a false negative? If not, why not?

Providencia stuartii may be a slow producer and it will take longer for the organism to change the media. In that case, one could make a "false negative" conclusion if one sought results too early.

2. What supplies the Carbon in this medium? Nitrogen?

nitrogen - urea carbon - dextrose (glucose)

1. Identify the components of the UREA AGAR recipe as the inhibitor, indicator, and selective, differentiated, nutrient and undefined components.

Inhibitor - indicator - phenol red selective - differentiated - nutrient - peptone, dextrose (glucose), agar undefined - yeast extract, peptone

6. Explain why it would be acceptable to record positive tests before the suggested incubation time is completed, but it is not acceptable to record a negative result early?

Sometimes you have really rapid hydrolysis. You may see the positive results earlier than expected, or later than expected. If the organism is slow to hydrolyze, one will have to wait longer, but once you see a positive result, one would not have to incubate any longer.

4. What is the evolutionary benefit of an organism capable of producing urease?

Urea hydrolysis provides nitrogen in a usable form and it also acts as a virulence factor for some pathogens by counteracting the environment.

3. What is urea? Where do we usually find it in the environment?

Urea is a product of decarboxylation of certain amino acids and is the primary nitrogenous waste in the urine of many land animals, including mammals.