Eosin Methylene Blue Lab Report

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Eosin Methylene Blue (EMB) is used to differentiate fecal coliforms, and is selective for gram negative bacteria. If bacterium is not a fecal coliform chances are it will be negative for growth and fermentation. Sterile EMB agar is dark red in color. If a bacteria ferments lactose it creates acid and changes the color of the colonies. If the bacterium ferments lactose quickly, the colonies will have a green metallic sheen. If lactose is fermented at a slower pace the colonies will be pink, and if no fermentation occurs the colonies will be colorless. When this test was performed on the unknown bacteria, the agar stayed red and the colonies were a green metallic sheen. This showed that the bacteria fermented lactose very quickly, had high amounts of acid and was some sort of fecal coliform.…show more content…
This test is called the Simmon’s Citrate test. Simmon’s Citrate agar contains sodium citrate which is the main carbon source, ammonium phosphate which is the source of nitrogen and brothymol blue (BTB) which is used as a PH indicator. If an organism uses citrate as its main source of carbon the agar will turn blue, which starts out as green prior to inoculation. If the agar turns blue after inoculation it is because the PH level of organisms that utilize citrate is above 7.5. In the unknown bacterium that was tested the Simmon’s Citrate test was negative, meaning the PH level was below 7.5 and there was no color change in the agar because citrate is not a carbon source in this

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