Escherichia Coli Identification Report

The identification of Escherichia coli as the unknown was concluded by a string of tests and observations such as gram-staining, shape, motility, oxidation, fermentation and citrate tests. This began with gram-staining the organism. After viewing beneath a light microscope, the unknown showed pink rods, proving to be gram-negative. The observation of motility was made by viewing the bacteria moving towards a specific direction. The next tests utilized in determining the unknown was oxidation tests such as oxidase, catalase and nitrate reduction tests. The most pertinent of these tests in the identification process was the oxidase test which was negative, meaning the organism is a facultative anaerobic. Though both the nitrate reduction and catalase tests resulted positive, neither were a deciding factor in determining the unknown. …show more content…
The organism proved to be negative in citrate utilization, narrowing done the options to just three unknowns. The final tests needed to decide the identity of the unknown were the lactose and urease tests. A positive lactose resulted, along with a negative urease test. These two final tests, along with the tests before, led us to the conclusion of the unknown identifying as Escherichia coli. Very often throughout the testing and identification process of an unknown, false negatives or false positives occur. While examining the results of the nitrate reduction test, a negative test was almost declared because of such a small amount of nitrogen gas trapped within the Durham tube. However as seen in the manual, E. coli partially reduces nitrate to a gaseous nitrogen, meaning the test was positive. Due to human error, what we almost concluded could have skewed the identification of the unknown. Luckily, the mistake was recognized early