Blog Post #5

In our most recent lab meeting Sammy and I tested our mystery microbe for catalase activity. To accomplish this we first tested some controls that we could compare our microbe to. We used a positive (S. epideidermis) control and a negative (E. faecalis) control.  We observed bubble formation with our positive control when a drop of 3% H2O2 was added and no reaction with our negative control.

 

We then added the drop to our microbe and observed bubble formation indicating a positive result for our catalase test. A potential explanation for the evolvement of catalase activity in certain microbe is the aerobic microbes adapting to fight against elements that anaerobic microbes do not encounter such as oxygen. 

 

The other experiment we did regarding our microbe was the triple sugar iron test to determine carbohydrate metabolism. The TSI slant provides the culture with an aerobic and anaerobic environment in which to grow. This allows us to observe how different bacterium ferment and metabolize. All five of our control tubes grew as expected. I compared the information provided to us about the predicted reactions for each bacterium and confirmed the results by observing the color of the TSI agar of each control after incubation.

E. coli

P. vulgaris

P. aeruginosa

B. Megaterium 

For our unknown microbe, the media at the top of the tube was pink/red indicating an alkaline reaction. The bottom, or butt ,of the tube was yellow indicating an acidic reaction. There was no evidence of hydrogen sulfide formation. These results mean that our microbe metabolized glucose 

but not sucrose or lactose.

In the last blog post, Sammy followed the dichotomous key up until the question regarding catalase activity…

Dichotomous Key

Below, I have used a dichotomous key in order to begin identifying our microbe…Below is the steps that I followed in the dichotomous key:

1. Gram Positive

2. Morphology, Rod Shaped (Bacilli)

3. Non-acid fast organism

Now we know that our microbe is catalase (+) so we can continue!

4. Catalase positive

We know that our microbe metabolized glucose in both the aerobic and anaerobic areas of the slant so I’m unsure of the answer to the next step in the key. We might have to have further discussions to determine the answer.