Unknown Culture Lab Report

Identification of bacteria within Unknown Culture #21
In this experiment, an unknown culture of two different types of bacteria was assigned to each person, a number of tests were performed to isolate and identify these bacterial cells. Based on knowledge from the previous experiments completed in lab, a basic understanding of each type of bacteria was used to create a flow chart that would aid the process of identifying the unknown bacteria within the culture. A gram stain that is performed initially will narrow down the types of tests certain bacteria will and will not respond to. In addition to the gram stain, some of the tests that were used include, a catalase test, an Eosin methylene blue (EMB) agar test, a bile esculin test, and a 6.5% sodium chloride (NaCl) test. If the catalase enzyme is present in the organism being tested then when in the presence of hydrogen peroxide (H2O2), the enzyme will convert the solution to water and oxygen, this can be observed bubbling of the organism when hydrogen peroxide is added to the test tube. EMB agar is both a selective and differential media; it is selective for gram-negative cells, in that when a gram-positive culture is plated there will be no colonies after incubation because the eosin and methylene dyes prevent the growth of gram-positive organisms, the

After 5 days the plates were removed from the cold room and the gram-negative test for Colony A on the EMB agar showed pink fisheye colonies which lead to the conclusion that the gram-negative organism within Unknown #21 was Enterobacter aerogenes. Had the pigmentation been metallic green, the organism would have been identified as Escherichia coli, and had there been no pigmentation at all a Triple Sugar Iron agar (TSI) test among other tests would have been