In order to identify an unknown bacteria, a variety of tests can be performed. The unknown bacteria that underwent some of these tests turned out to be Escherichia coli. Gram stain, citrate utilization test on Simmons citrate agar, and urease test with phenol red were performed on the assigned bacteria. The unknown bacteria was determined to be E. coli as testing concluded the sample was Gram negative, bacilli, citrate utilization negative, and urease production negative. It is concluded that E. coli cannot use citrate as the sole carbon source and it cannot convert urea into ammonia and carbon dioxide.IntroductionIt is important in microbiology to be able to identify an unknown microorganism . Numerous assays characterizing the functions of bacteria have been developed to accomplish this task. The unknown bacteria tested turned out to be Escherichia coli. E. coli is a Gram-negative bacillus bacteria. Gram negative means that there is an outer membrane surrounding the thin peptidoglycan layer of the cell. Bacillus means the bacteria is rod shaped. E. coli were identified as Gram-negative bacilli and following Gram staining. A Gram stain uses crystal violet as the primary stain and safranin as a counterstain (1). Gram-positive bacteria have a very thick layer of peptidoglycan in their cell wall. This thick cell wall will remain stained purple by the crystal violet-iodine complex, and Gram-negative bacteria will be decolorized and stained pink from the safranin counterstain (1). The thickness of the peptidoglycan layer determines whether it is colored pink or purple. To test an organism's ability to use citrate as a carbon source, a citrate utilization test is performed. This test is...... middle of paper...... n dioxide. The ammonia would make the pH of the broth alkaline, which would make the broth bright pink (3). Since the broth remained the same orange/yellow color, we know that the urea in the broth was not broken down into ammonia, which means the body is not producing the urease enzyme. Literature cited1) Bartholomew, JW and T. Mittwer. 1952. The Gram stain. Microbiology and molecular biology journals. 16:1-29.2) Krajewska, B. 2009. Ureases I. Functional, catalytic and kinetic properties: a review. Journal of Molecular Catalysis B: Enzymatic. 59:9-21.3) Roberts, GD, CD Horstmeier, GA Land and JH Foxworth. 1978. Rapid test of urea broth for yeast. Journal of Clinical Microbiology. 7:584-588.4) Vaughn, RH, JT Osborne, GT Wedding, and J. Tabachnick. 1950. The use of citrate by Escherichia coli. Journal of Bacteriology. 60: 119-127.