Mannitol Salt Agar:
Above are the agar specimens in which our bacteria grew! Mannitol Salt Agar isolates bacteria based on salt tolerance, and differentiates it by its ability to ferment Mannitol. Fermentation is evident when the agar medium changes from red to yellow. Since the foundation on which our bacteria grew remained red our bacteria cannot ferment Mannitol. However, because it grew in this agar, it is proved that our bacteria must be of the genus Staphylococcus because this genus is the only one that is able to grow in a high salt concentration (also known as a Halophile).
MacConkey Agar:
The pictures above are from the MacConkey Agar Test. As evident by the lack of visual growth, our bacteria did not thrive in this environment. This is because MacConkey agar differentiates between gram-negative enteric bacilli, based on their ability to grow and ferment glucose. It keeps our results consistent, since our bacteria is not gram-negative nor a bacilli. In the first picture, the right side of the agar plate had much growth and was able to ferment lactose, only because it was not our bacteria, but another specimen from the class. Lactose fermentation is evident by the pinkish color appearing in the agar.
Eosin Methylene Blue (EMB) Agar:
The picture above depict the EMB Agar test that was carried out last class. As seen by the visual aids, there is no growth on our portion of the agar plate. This is also consistent with our data because the purpose of this media is to isolate and differentiate gram-negative enteric bacilli. Since, our bacteria is neither gram-negative nor enteric bacilli, it makes complete sense! The other sample (on the right side of the top picture), though hard to depict from our picture, has a green metallic color to it. This proves that our friend has bacteria that can ferment lactose. Ours, obviously, cannot.
Catalase Test:
We added hydrogen peroxide to the sample that grew (Mannitol Salt Agar) our bacteria, to test if it had the enzyme catalase. Since bubbles formed on our bacteria the hydrogen peroxide was successfully broken down into water and oxygen. This proves that our bacteria is an aerobe. Previous tests have also shown that our bacteria fits this description as well, being a facultative aerobe.
We are getting so close to finding out the identity of "F"! Next class we should be able to completely identify him for sure, but for now we have a guess! We hypothesize that "F" is Staphylococcus epidermidis.
Join us next time when we find out if we were right!
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