reaction in the phenol red broth

Unknown Identification Results

Unknown Number:


Slant Pigmentation:


Gram Stain:


Cell Morphology:


Cell Arrangement:


Streak for Isolation:

Isolation of colonies did not occur

Colony Morphology:

Unable to identify

Phenol Red Fermentation







Guess Your Bacteria After:

Week 1:

Micrococcus luteus

Week 2:

Pseudomonas aeruginosa

My unknown bacteria is Pseudomonas aeruginosa. Based upon the Gram Stain provided, the unknown was determined to be Gram-negative. This was interpreted based on the cells being stained pink. In addition, the microorganism’s shape appeared to be rod-like and in a single arrangement. They were seen individually and not in a group or cluster. From all three sugars of glucose, sucrose, and lactose, none of them developed a reaction in the phenol red broth. These results are presented as red test tubes with no bubbles. A lack of reaction based upon these images mean there is no fermentation of carbohydrates. The streak plate provided did not display single individual colonies. They remained in big clusters, allowing no identification to be done. The pigment present is neon green. Due to the unidentifiable nature of the streak plate’s results, the colony morphology was undetermined.


The method used to determine the unknown was through comparison of my identified results and the chart of organisms. By identifying carbohydrate fermentation, all organisms were eliminated with the exception of Micrococcus luteus and Pseudomonas aeruginosa. The official determination of the unknown organism is when the gram-negative result was determined. It eliminated the micrococcus luteus organism, and kept the current identified organism. To ensure the organism was right, the pigment color was checked and determined to match the image provided.

Work Cited:

Leboffe, M.J., Pierce, B.E. (Eds.). (2016). Microbiology Laboratory Theory & Application (3rd ed.). Morton Publishing.


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