Unknown Lab

Discussion The possible identity of the unknown organisms in the mixed culture was limited to bacteria that we had worked with previously in lab. Initially a Gram stain was conducted in order to distinguish the unknown bacterium as a Gram-positive and/or a Gram-negative organism (Lancaster and Bennett, 2012; Kellenberger, 2001). Based upon the results, both Gram-negative and Gram-positive bacteria were observed in the unknown mixed culture (Table 1 and Table 2; Kellenberger, 2001). In order to isolate the two different bacteria, colonies that grew on the MSA were used to inoculate Gram-positive tests, where as MacConkey Agar colonies were used to inoculate Gram-negative tests. Once the colonies were isolated and the appropriate Gram-negative and Gram-positive tests were conducted, the identification of both unknown organism were fairly easy. The results from the Coagulase test, the Oxidase test, and the Nitrate test were used to help identify the unknown Gram-positive bacterium. The coagulase test was negative, therefore of all the possible Gram-positive bacterium the unknown organism could either be Staphylococcus simulans or Micrococcus luteus (Table 3; Lancaster and Bennett, 2012). Next, the Nitrate test was used to differentiate between the two remaining possibilities. Since the unknown Gram-positive bacterium resulted in a negative for Nitrate, the organism was identified as Staphylococcus simulans. As for the identification of the unknown Gram-negative bacterium, the unknown bacterium’s ability to ferment lactose was analyzed first. Positive lactose fermentation was indicated on both the MacConkey agar plate and SSA by the growth of bright pink colored colonies (Table 2; Kenyon College, 2011; Lancaster and Bennett, 2012). Identical results were also found in the inoculated lactose broth with the Durham tube and the TSI tests, which both indicated positive fermentation for lactose as well (Lancaster and Bennett, 2012; Watson, 2013;

Cited: Anonymous. 2013a. Pure culture. http://www.britannica.com/EBchecked/topic /483854/pure-culture Anonymous Anonymous. 2013c. Types of culture media used to grow bacteria. http://www.sc ienceprofonline.org/microbiology/types-culture-media-for-growing-bacteria.html Anonymous Collin, B. 2013. Salmonella-shigella plates. http://iws2.collin.edu/dcain/CCCCD %20Micro/salmonellashigella_plates.htm Frankhauser, D Kellenberger, M. 2001. Exploring the unknown. http://www.ncbi.nlm.nih.gov /pmc/articles/PMC1083810/ Kenyon College Department of Biology Lindquist, John. 2013. Bacteriology 102: A general overview of coliforms. http://www.splammo.net/bact102/102coliforms.html Rollins and Joseph Tortora, G. J., Funke, B. R., and Case, C. L. 2009. Microbiology: An Introduction Usinger, B Watson, R. 2013. Biochemical tests. http://www.uwyo.edu/molb2210_lab /info/biochemical_tests.htm#oxidase Watson, R Anonymous. 2013e. http://www.mesacc.edu/~johnson/labtools/Dbiochem/imvic.html Table 1