Microbiology Unknowns Paper


Unknown Write-Up


















Daniel Contreras
Microbiology P106
Mrs. Shaunna Callison
Spring 2015
May 13th 2015

          Today, each of us received two unidentified bacterial specimens. Both tubes contained different bacterium growing on nutrient agar slants; and, one tube was labeled 40-A while the other tube was labeled 40-B. Each of us prepared two backup tubes (one tube for each specimen) in case of accidental contamination. I labeled these backup tubes 40-A copy and 40-B copy. The bacteria that I received had the possibility of being two of the following thirteen bacteria: Enterococcus faecalis, Bacillus subtilis, Bacillus megaterium, Staphylococcus aureus, Staphylococcus epidermis, Micrococcus roseus, Micrococcus luteus, Proteus vulgaris, Escherichia coli, Citrobacter freundii, Enterobacter aerogenes, Alcalagenes faecalis, or Pseudomonas aeruginosa. After I completed my two backup tubes, I performed my first step in identifying what my two bacteria were: the gram stain test.

          I ran a gram strain test to determine which bacteria was gram positive and which bacteria was gram negative. Gram positive bacteria are blue/purple when viewed under a microscope while gram negative bacteria appear pink/red. My results from the gram stain concluded that specimen 40-A was gram positive because it appeared purple after viewing it under the oil immersion lens using a microscope. Specimen 40-A had the potential to be one of the following gram positive bacterium: E. faecalis, B. subtilis, B. megaterium, S. aureus, S. epidermis, M. roseus, or M. luteus. On the other hand, specimen 40-B was identified to be gram negative due to it appearing red/pink in color under the microscope's oil immersion lens. Thus, Specimen 40-B was one of the following gram negative bacteria: P. vulgaris, E. coli, C. freundii, E. aerogenes, A. faecalis, or P. aeruginosa.

Explanation for Specimen 40-A:

            For my gram-positive specimen, 40-A, I performed a gelatin test. A positive test on the gelatin would mean that my specimen had to be either B. subtilis, B. megaterium, or S. aureus. On the other hand, if I had a negative test then my bacteria could be either E. faecalis, S. epidermis, M. roseus, or M. luteus.
            After a few days of incubation, I viewed the outcome of my 40-A gelatin test. After putting the 40-A specimen on ice for 4 minutes, I found out that it was positive for gelatinase because the media did not solidify. Therefore, it could not be E. faecalis, S. epidermis, M. roseus, and M. luteus. My unknown bacteria in 40-A has the possibility of being either B. subtilis, B. Megaterium, or S. aureus. The next step is to run a phenylalanine deaminase test on specimen 40-A. A positive result on the phenylalanine deaminase test would mean the bacteria had to be B. megaterium. Oppositely, a negative outcome would mean the specimen would have to be either B. subtilis or S. aureus.
          Today, I viewed the results on my phenylalanine deamination test for my gram-positive 40-A specimen. I got a negative outcome because the media did not turn dark green; therefore, it could not be B. megaterium.  The only possibilities that my bacteria could be are B. subtilis or S. aureus. In order to identify my bacteria, I ran a Moeller Ornithine decarboxylation test on my 40-A specimen. If I get a positive result on the decarboxylation test, then my bacteria would have to be B. subtilis. On the other hand, a negative result would mean my bacteria is S. aureus.
            My specimen in 40-A revealed a positive result after running a Moeller Ornithine decarboxylation test. Therefore, my unknown for 40-A is suspected to be B. subtilis. To confirm, I ran a urea confirmation test on specimen 40-A because B. subtilis would produce a positive result.
            After waiting a couple days, I got a positive result on my urea confirmation test because the media turned into a fuchsia/hot pink color. Therefore, the test confirmed that the specimen in 40-A is indeed B. subtilis.




Explanation for Specimen 40-B:

            First, I ran a citrate test for my gram-negative 40-B specimen. If I get a positive result, then the bacteria would have to be either C. freundii, E. aerogenes, A. faecalis, or P. aeruginosa. If I get a negative result, the specimen could be either P. vulgaris or E. coli.
            After incubating it, I reviewed the results on my citrate test for the gram-negative, 40-B, specimen. The media on the citrate agar plate produced a negative result because the media did not turn into a Prussian blue (due to the absence of the enzyme citrase.) That test eliminated the possibilities of the bacteria being C. freundii, E. aerogenes, A. faecalis, and P. aeruginosa. Therefore, the only possibilities that the 40-B specimen could be are either P. vulgaris or E. coli. In order to determine which of the two it was, I performed a gelatin test on specimen 40-B. A positive result on the gelatin test would mean 40-B had to be P. vulgaris; oppositely, a negative result would mean the specimen was E. coli.

After a few days, I viewed the results on my gram-negative, 40-B, gelatin test. The result was negative for gelatinase because it remained a liquid; thus, it revealed that my bacterial species for unknown 40-B is E. coli and not P. vulgaris. However, I chose to run a Moeller Ornithine decarboxylation test on 40-B to confirm that it was indeed E. coli.
          After reviewing the results on my 40-B Moeller Ornithine decarboxylation confirmation test, the outcome was positive due to the purple color of the media. Therefore, my unknown bacteria is indeed E. coli.


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