The purpose of this lab was to identify an unknown bacteria culture using differential tests. The identification of the unknown culture was accomplished by identifying the bacteria based on its specific metabolic characteristics and morphology. It is suggested that culture 11 is a sample of Enterobacter aerogenes.
This experiment was centered on metabolic and biochemical testing procedures. The rationale of performing these tests was to distinguish six different microbes from one another and to compare how their metabolic and biochemical processes differ from species to species to determine the unknown sample. The tests included: Triple sugar iron agar (TSAI), the Sulfide Indole Mobility (SIM) test, Glucose fermentation, the Methyl Red test, the Voges-Proskauer test, Citrate test, the Urease Test, and finally the Gelatin test. The microbes that were tested during this lab were: Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, and Salmonella typhimurium. The sample labeled #11 could have been any of the six microbes.
A gram stain was performed to assess the shape and other characteristics of the bacteria, and to ensure that there was no gram positive contamination. Gram positive cells have a thick outer peptidoglycan layer that traps the crystal violet-iodine complex more than gram negative cells. As a result, they are less vulnerable to the de-colorization step with alcohol making them appear purple in color, while the gram bacteria negative appear pink.
Triple sugar iron agar slant tests for multiple things: sugar fermentation of glucose, lactose, and sucrose, and the production carbon dioxide and hydrogen sulfide. The gases are easy to identify. If any carbon dioxide is produced cracks or bubbles appear inside of the medium, and sometimes enough CO2 is produced to push
References: http://www.microbelibrary.org/component/resource/laboratory-test/2842-triple-sugar-iron-agar-protocols http://www.condalab.com/pdf/1514.pdf http://faculty.deanza.fhda.edu/gilleskay/stories/storyReader$80 http://www.dalynn.com/docs/RC90-25.pdf BIOTECHNOLOGY PROCEDURES AND EXPERIMENTS HANDBOOK S. H ARISHA, PH.D