Gram Positive and Gram Negative

Gram Positive and Gram Negative

  • Submitted By: tylerreid
  • Date Submitted: 02/14/2014 8:31 PM
  • Category: Science
  • Words: 1111
  • Page: 5
  • Views: 44

Colony morphology, gram stain, enzymatic, microscopic, selective and differential examinations on pure strains of unknown laboratory sample to reveal the identification of the unknown #5

Objective: The sample of mixed culture that has one gram positive and one gram negative culture has been provided. After isolating them to two separate pure colonies, we use various research techniques to differentiate and identify the two pure cultures. The techniques include investigation of colony morphology, gram stain, enzymatic testing, and selective and differential plating testing. Since the mixed culture had two different species of bacteria, the outcome would be one bacterium from Gram positive and one from gram negative species. Following the phylogeny for gram negative and positive bacteria, the selective and differential tests will be able to provide the exact genus and species of two unknown bacteria. Also, the bacteria will have distinct visible changes when they are tested under selective and differential medias.

Material and Methods:
The material and methods are outlined in the laboratory manual:
“Microbiology 265, Introductory Microbiology, Laboratory Manual”, pg. 30-46


Figure 1
Identifications such as colony morphology, growth rate, gram stain, oxidase and catalase test of two isolated colonies from unknown #5 (small colony = #1 and big colony = #2)

Unknown #5 | Colony Type #1 | Colony Type #2 |
Colony Morphology | Circular, Entire | Circular, Undulate |
Growth Rate | Slow | Fast |
Gram Stain Results | Purple (Gram positive) | Pink (Gram negative) |
Oxidase Test | No change (Negative) | No change (Negative) |
Catalase Test | No bubbles (Negative) | Bubbles (Positive) |

Two different colonies were examined, small colony (#1) and big colony (#2). Results from five different sections were distinct enough to differentiate the two. During the gram staining, we microscopically observed the two slides and the type #1 slide had...

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