Question

Discussion 1. Metabolic tests look for the presence of a specific metabolic pathway or enzyme found in bacteria. How might this information be useful in the development of new antibacterial drugs? 2. How can you tell if the enzyme being tested for on a plate is an exoenzyme instead of an endoenzyme? Why is gelatin not used as a solidifying agent in microbiological media? 3. Newer tests like PCR can identify an unknown bacterium by looking for specific DNA sequences. This is potentially very useful in medical diagnosis. Given an unknown bacterium, discuss the benefits and risks of running standard metabolic "profiles" vs PCR testing 4. What is the purpose of a differential medium? 5. What is the purpose of a reagent, and which labs used added reagents? Lab 13-Introduction to Metabolic Testing

Answer 1

1. If a specific metabolic pathway is identified in a bacterium then the inhibitors against specific enzymes or signaling intermediates can be designed. The administration of such specific inhibitors can result in inhibition of the growth of specific bacteria in which that metabolic pathway is present.

2. We should have the substrate for the enzyme and the detection method of the product formed by the enzyme handy. Now if we get the product by using only the culture medium in which the bacteria was growing and not from the cell then the enzyme is an exoenzyme. But if we get the product only using bacterial cells, then it is an endoenzyme.

There are two reasons to use agar-

a. The melting point of agar is 100 degree Celcius. But the melting point of Gelatin is 27 degree Celcius.

b. The nutritional value of agar is much less than that of gelatin which means a very less number of bacteria can feed on agar.

3. If the bacteria is unknown then it is not possible to know the sequence of its genome in earlier hand. If we do PCR then we can identify the bacteria which is closely related to the unknown bacteria. Sometimes false-positive results can also come for example you cannot separate Shigella and E.coli by PCR.

But by metabolic tests you can characterize the bacteria biochemically which can help you to identify the bacteria based on some specific pathways present in it. But this method cannot pinpoint the genus and species of the bacteria. For that, you have to do 16srRNA sequencing.

4. Differential medium has some specific metabolites which are defined. So they will facilitate the growth of certain bacteria but do not support the growth of others who cannot metabolize those metabolites present in the medium. In this way, they separate specific kinds of bacteria from the others.