Identification of an Unknown Bacterial Species

Topics: Bacteria, Streptococcus, Agar plate Pages: 3 (784 words) Published: April 18, 2011
MIC 230
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...
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