Unknown Identification Report The objective of this experiment was to identify an organism from a mixture of two unknown bacterial species. In order to accomplish this, I first plated my unknown mixture on Tryptic Soy Agar (TSA), Columbia Naladixic Acid (CNA), and MacConkey’s Agar (MAC) plates. After 48 hours of incubation, it was unclear that two different bacterial colonies had grown on my TSA plate. Only one type of colony was evident. However, it was apparent that I had successfully isolated two different bacterial species by examining my MAC and CNA plates. Only one type of colony had grown on my MAC plate indicating a gram negative species, which I chose to be organism A. Similarly, only a single type of colony had grown on my CNA plate, indicating a gram positive species, which I chose to be organism B. By performing a gram stain on the two colonies I was positive they were two different species because organism A were gram negative rods in single arrangement and organism B were gram positive cocci arranged in irregular clusters. I ran a catalase test on both organisms; organism A was catalase positive while organism B was catalase negative. I also performed a cytochrome oxidase test on both organisms; again, organism A was oxidase positive while organism B was oxidase negative. Then I decided I would run the biochemical tests on organism B. I observed that organism B was non-motile and did not produce endospores. With these results, I narrowed down the possible species to Enterococcus faecalis, Enterococcus faecium, Lactococcus lactis, Leuconostoc mesenteroides, Pediococcus parvulus, and Streptococcus mitis.
After obtaining some background information on these bacterial strains in the Strain Information handout, I decided to inoculate an arganine decarboxylase broth and a sheep blood agar plate to narrow down the possibilities of my unknown species. After incubation, I found that my organism tested positive in an arganine decarboxylase broth
References: 1. Carniol, K. and M.S. Gilmore. 2006. The comprehensive sourcebook of bacterial protein toxins, p. 717 3rd ed. Alouf, J.E., and M.R. Popoff (ed), Academic Press, San Diego, CA. 2. Madigan, M.T., and J.M. Martinko. 2006. Brock biology of microorganisms. p. 707 and 781 11th ed. Prentice Hall, Upper Saddle River, NJ. 3. Rollins, D.M. and S.W. Joseph, Accessed 5 April 2011, Pathogenic Microbiology, http://ww w.life.umd.edu/classroom/bsci424/PathogenDescriptions/Enterococcus.htm, August 2000. 4. Winfrey, M.R., M.A. Rott, S.J Anglehart, W.R. Schwan, B.C. Taylor, D.J. Grimes, and R.M Burns. 2010. Laboratory manual for fundamentals of microbiology: isolation and identification of unknown organisms from mixed culture, p. 21-1 – 21-5 and 1 – 4 . Department of Microbiology, UW-La Crosse, WI.