Unknown Bacterium Identification Utilizing Multiple Testing Porsha Sanders BIOL 3444_009; Matthew Nelson; April 16, 2015 The objective of this experiment is to determine an unknown bacterium by applying several tests and comparing with known results. Through utilization of a Triple Sugar Iron Agar test, a Sulfate Indole Motility test, a Methyl Red and Vorges-Proskauer test, a Citrate test, a Urease Hydrolysis test, and lastly ,a Gelatin test, the unknown bacterium was narrowed down to E. coli. Important conclusions of this experiment were that many tests can be used for identification besides a simple gram stain. Introduction There are several ways to identify unknown bacteria. The first way of identification is gram stains. When a cell is …show more content…
This test also determines if organisms produce the enzyme citrate-permease. For these organisms, citrate is a single source of carbon. Thus, this enzyme helps in transporting the citrate molecule into the cell to be turned into pyruvate. The media itself is green initially and contains the indicator Bromthymol blue dye. It also contains sodium citrate and ammonium phosphate. Bacteria that uses citrate also changes the ammonium phosphate in the media into N₃H+ NH₄OH causing the pH to rise and the media to become more alkaline. A positive result is a blue color change signifying that the pH rose to 7.6 or above. A negative result is no color change leaving the media green (Leboffe and Pierce 2010) Urease Hydrolysis is a test that defines if urease production is present. Hydrolysis is the reaction of complex molecules being divided by a water molecule. Urease, an intracellular hydrolytic enzyme, hydrolyzes urea into ammonia and carbon dioxide. The media used for this is an orange urea broth constructed from yeast extract and urea and contains phenol red as an indicator. A positive result is the broth turning pink signifying the pH was raised (Leboffe and Pierce …show more content…
Based off the results only three could possibly yield a yellow slant/ butt and produce gas. Those were Escherichia Coli, Enterobacter aerogenes, and Klebsiella pneumonia. Next tests that were analyzed were the MR and VP. E. coli and K. pneumonia should have positive results like the ones I produced for MR and the same two bacteria should yield a negative result for VP. The next test I analyzed was SIM. All three of the previous bacteria were negative for sulfur reduction and only E. coli and E. aerogenes were positive for weak motility. However, only one out of all of the bacteria was positive for indole production and that was E. coli. Based off of the previous MR-VP test and the motility test, it could not be E. aerogenes or K. pneumonia. Last test I used to be positive my notion that E. coli for sure was my unknown was citrate. Since only one bacterium (E. coli) should have a negative result out of all of the bacteria all signs pointed to me being correct. I continued reading all of the other tests that took more time to be observed beginning with Urease to make sure based off of the previous tests I analyzed that I knew for sure my unknown. For my results for urease, only E. aerogenes and E. coli yielded negative results, but based off of the other test results E. aerogenes did not match. Lastly, for gelatin, E. coli matched the negative result. In summary, all of the tests