to ferment lactose. This test is accomplished by placing the bacteria on Eosin Methylene Blue agar. The agar is selective for gram negative bacteria and those bacteria that can ferment lactose will have colored growth, usually a metallic green sheen. The Sulfur Indole Motility agar tests for three separate characteristics; sulfur reduction, indole production, and motility. The SIM medium is a semisolid medium; this facilitates the motility test. The medium contains sulfur, if the bacterium has the ability to reduce sulfur the medium will turn black. The medium also contains tryptophan. If the bacterium has the enzyme tryptophanase, indole will be produced. A positive result will be a pink ring around the top of the medium after Kovac’s solution has been added. The Urease test detects the presence of the enzyme urease. This medium contains urea and a pH indicator, phenol red. A bacterium containing urease will produce ammonia, which raises the pH and changes the color of the medium. A positive test shows a color change from a reddish orange to pink.The fourth test used to identify gram negative bacteria is the Simmon’s Citrate Utilization test. This test measures a bacteria’s ability to use citrate as its sole carbon source for metabolic pathways. This solid medium contains Bromothymol Blue, which serves as a pH indicator. If the bacteria can break down citrate it produces carbon dioxide that reacts with sodium and water, also found in the medium, to produce sodium carbonate. Sodium carbonate elevates the pH causing a color change from green to blue (a positive result).The second bacterium was gram positive. There are three tests that are used to identify gram positive bacteria. The three tests are hemolyses on blood agar, Mannitol fermentation on mannitol salt agar, and the coagulase test using plasma-containing serum in coagulase tubes.The test on blood agar tests for a bacteria’s abilit...
