Dr. Nathan Cahoone
December 9, 2010
There are many reasons for knowing the identity of microorganisms. The study and test was done by applying all of the methods that have been learned so far in the microbiology laboratory class for the identification of an unknown bacterium which I was using unknown #25.
Unknown #25 had the following morphology on a streak plate: medium sized butyrous cream colored colony. Gram-staining was utilized as a first step to differentiate between gram-positive and gram-negative. After determining that it was a Gram negative single bacillus, biochemical tests performed and their purpose and results are shown in table and flow chart form.
Table 1: biochemical Test Results Test | Purpose | Reagents | Observations | Results | Gram stain | To determine the Gram reaction of the bacterium | Crystal violet, Iodine, Alcohol, Sarasin | Pink rod | Gram-negative rods | Carbohydrate (Glucose) fermentation | To determine the ability of a bacterium to fremnet a carbohydrate, make acid or gas | Durham tube | Color change from red to yellow, bubble in Durham tube | Positive carbohydrate fermentation, acid production and gas production | Tryptophan digestion | To determine the ability of an organism to split indole from tryptophan | Kovac’s drop added to tryptone broth | Kind of colorless and list green ring at top of broth | Negative tryptophan digestion | Cystine digestion | To determine the ability of an organism to catabolize certain amino acids | Iron ions | Color didn’t changed remaind creamy | Negative cystine digestion | Citrate Utilization | To determine the organism is able to utilize citrate as a carbon source | Citrate slant (green) & Bromthymol blue | Color changed from green to deep blue | Positive for citrate utilization | Urea digestion | To determine the ability of an organism to catabolize ammonia | Phenolmed | Color didn’t change stayed bright