Day 6

Today in lab, we observed that our unknown bacteria is an obligate aerobe and it is motile.

In this test tube, bacteria only grew on top. This means that the bacteria can only grow where there is oxygen. The bacteria didn’t grow on the bottom of the tube because it would require the bacteria to grow in carbon dioxide instead of oxygen. The technical term for our bacteria is an obligate aerobe.


For this second test tube, the bacteria was stabbed with an inoculating needle into a semisolid agar. This test proves that the bacteria is motile because the bacteria appears to be growing out from the line of inoculation. In the case of motility, the cells swim away from the stab and a diffuse “cloud” of growth extends from the stab. This is what we observe in the test tube.



Then, we completed more tests in order to figure out the type of bacteria we are observing.


The first four tests we completed were starch, gelatin, casein and triglyceride hydrolysis test. We performed the tests in order to determine the bacteria’s ability to hydrolyze carbohydrates, proteins, and fats by testing if the bacteria has specific enzymes.

Casein is the major protein in milk. This test is used to assess the production of proteinases.

Gelatin is an animal protein. This test is used to assess the production of gelatinase.

Starch is a carbohydrate. This test is used to assess the production of amylase.

Triglyceride is a lipid. This test is used to assess the production of liapases.

Next, we completed two different tests called methyl red test, and voges-proskauer test. The purpose of the MR test, is to determine the ability of the bacteria to ferment glucose through mixed acid fermentation. The purpose of the VP test is to determine the ability of the bacteria to ferment glucose through butanediol fermentation.

Next, we completed three more tests called Triple Sugar Iron AgarTest, Litmus Milk Reactions Test, and Indole (Tryptophan Degradation) Test. The purpose of the TSI test is to determine the bacteria’s ability to ferment glucose, lactose and sucrose and to produce H2S. The purpose of the Litmus Milk Reactions is the differentiate the ability of the bacteria to utilize lactose, protein, and litmus in litmus milk. The purpose of the Indole test is to determine the ability of the bacteria to split amino acid tryptophan into indole and pyruvic acid.

Lastly, we put carbon dioxide on one of the inoculated plates. When doing this, bubbles formed and this means that cataylase is present in our bacteria.