What Is Gram Staining?

Identification of Unknown # 15

Abstract. One of the most fundamental differential staining techniques used in the study of bacteriology is gram staining. There are two main types of bacteria, gram negative and gram-positive. The purpose of this experiment was to perform a variety of tests to identify the bacteria contained in the unknown sample labeled number 15. The following are the tests that were used to identify the two different bacteria. The SIM test, which tests for sulfur reduction, indole production, and motility, MRVP which is a test used to distinguish different organisms within Enterobacteriaceae, the citrate test which is used to identify
The indole test for this method is the same method as listed above in the SIM testing method. The methyl red and the Voges-Proskauer tests are used to distinguish different organisms within Enterobacteriaceae. This process is done by performing a mixed acid fermentation test by adding methyl red to an MR-VP medium and then observing their ability to convert acidic fermentation products to non acidic products by using the Voges-Proskauer test and the VP reagent (Choi 2014). A positive MR test has a noticeable red tinge due to the vast amounts of acid being produced. A positive VP test has immiscible layers of red and yellow, where negative results would indicate immiscible layers of a copper/brown color. Citrate is a derivative of citric acid. The citrate test identifies organisms, using the Simmons Citrate medium, that use citrate as their means of carbon and energy and can also differentiate different members of Enterobacteriaceae. A blue color or any kind of bacterial growth indicates a positive result and a green color indicates a negative result (Gallup
The MacConkey test was then used to confirm these results, since it has the ability to select for gram negative bacteria (Figure 9). With negative results for this test, a variety of bacteria were able to be eliminated from the list of bacteria, including Staphylococcus aureus, Pseudomonas aeruginosa, and Enterobacter aerogenes. The EMB test (Figure 10), helped to further eliminate more bacteria including E. Coli. This confirmed our results along with the negative results for the Indole test and the Sulfur reduction test (Figure 6). What ultimately led to our conclusion after comparing our results was the positive catalase test, which indicated that we in fact isolated the bacteria and got results that confirmed that one of our bacteria was in fact Staphylococcus aureus and one was not, and with the other tests eliminating a vast majority of the bacteria we were able to conclude that Klebsiella pneumonia was the other bacteria within the unknown (Table 1, Figure