Media and Their Purposes Flashcards
What do C-agars do and what do they tell us about organisms being grown on them? What ingredient in their composition tells us this information? What does a positive and negative result look like?
C-agar demonstrate an organisms’ ability to ferment the sugar of the C-agar. The ingredient in the media is a sugar, typically either glucose, lactose or sucrose. A positive result is the media turning a yellow color.
What does nitrate broth do and what do they tell us about organisms being grown on them? What reagents do you add to it to get results? There are multiple different “positives” for this media, know what each tells you.
This tells us whether or not the media can reduce NO3 to NO2 or N2 free gas. To get results for this media you add SA and DMN first, then Zinc if necessary. If the media does not change color after the addition of SA and DMN then there is no nitrate present. If the color does change with the addition of SA and DMN then the organism can reduce NO3 to NO2. If there is a red color change after the addition of zinc then there is nitrate present but is not reduced. If there no color change after the addition of zinc dust then the nitrate was reduced to something else, such as N2.
What does motility nitrate agar deeps tell us about the organism? What does a positive result look like?
Whether or not the organism is motile. A positive result looks like a red color through the media. A pink and red color develops through the breakdown of nitrate to nitrite.
What does tryptone broth test for? What does it tell us about the organism? What reagents do you add to this media? What does a positive result look like?
The ability of the organism to breakdown tryptophan to indole by detecting tryptophanase. You add Kovac’s reagent. A positive result is a red ring at the top of the media.
What does starch agar tell us about the organisms that grow on it? What does this media contain? What reagents do we use it for? What does a positive result look like?
It detects the presence of amylase enzyme in the organism. The media contains starch. We use Gram’s Iodine. A positive result is a clear zone around the colony.
What does a blood agar plate tell us about an organism? What is the difference between the hemolytic patterns?
It tells the organisms’ ability to produce hemolysins which are enzyme that damage/lyse red blood cells.
Gamma: no breakdown of red blood cell - no zone of lysis
Alpha: partial breakdown of red blood cell - green/brown zone
Beta: complete breakdown of red blood cell - clear zone of lysis
What does the slide catalase test tell us about organisms? How does this test work and what reagents do we use? What does a positive test look like?
This tells us if the organism contains the enzyme catalase. This test works by adding hydrogen peroxide to the organism and watching for a reaction. The chemical equation is: H2O2 –> H2O + O2(g). A positive result looks like bubbling where the hydrogen peroxide was added.
What does an oxidase test tell us about an organism? What does a positive result look like?
This tests for the presence of cytochrome oxidase. A positive result looks like a dark blue/purple color appearing on an oxidase strip within a few seconds of adding a colony of the bacteria.
