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Unknown Lab Report

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In Microbiology Lab 3 I chose the unknown culture #14 and ultimately identified it as Staphylococcus epidermidis bacteria. On a microscopic level I found the organism to be gram positive with a coccobacillus shape and both tetrad and cluster cell arrangement. I performed an isolation streak with S. epidermidis on Nutrient Agar which resulted in pinpoint, round, entire, and flat macroscopic morphology. I took a loopful of the organism from the Nutrient Agar and placed it on a slide to perform the catalase test. I added a few drops of 3% Hydrogen Peroxide and it resulted in bubble formation. The positive gram stain and positive catalase test indicated that the organism belonged to the Staphylococcus Genus, which meant it was now time to pinpoint the species based on differential and selective biochemical tests.

                To ensure that my genus identification was correct I performed a Bile Esculin Slant with a fish tail streak on my unknown bacteria. This test resulted in neither growth nor a black precipitate; therefore I could conclude that my unknown was not Streptococci or Enterococci but indeed Staphylococcus. Next I observed the isolation streak on my Blood Agar Plate and found pinpoint, round, entire and flat colony morphology as well as an alpha hemolytic reaction pattern, indicating red blood cell ion leakage which is characteristic of S. epidermidis. The final test used Mannitol Salt Agar that selects for Staphylococcus bacteria because they are salt tolerant and differentiates between species based on agar color.   The agar remained red after incubation with my unknown culture indicating that the Mannitol-D sugar was not fermented. After running this series of test I can accurately conclude that my unknown #14 culture was Staphylococcus epidermidis.

At age 11, Jonathan Markway was diagnosed with congenital heart disease. Jonathan’s doctor found a systolic heart murmur in his aorta due to a thickened tricuspid valve causing turbulent flow. A few...

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