Biology lab report (staphylococcus aureus)


Format for “Bacterial Unknown Identification” lab report


  • The report must be typed
  • Your unknown # must be clearly indicated at the beginning of the report
  • All results must be tabulated and labeled clearly. It should be obvious to the reader what procedures were used and what results were observed.
  • Write in the past tense
  • Results section must include the following information:
  • Colony characteristics (color, size, shape, margin, elevation, texture)
  • Cellular characteristics (Gram stain reaction, cell size, cell morphology, cell arrangement)
  • Either oxidase or catalase test results
  • Effect of environmental factors (temperature, pH, osmotic pressure, oxygen requirement)
  • any biochemical tests used in the positive identification of the unknown (Ex. 31, 32 or 33)


Title…should be stated clearly on the first page of your report


Purpose…should include a few concise sentences describing the goal of the exercise


Procedures/Results…In chronological order, describe the procedure followed immediately by its results.  You should briefly summarize the procedure and make sure you indicate what sample was used as inoculum, what media was inoculated, and time/temperature of incubation.  (For example: BHI media was inoculated with the liquid broth of unknown #1 and incubated at 37 deg for 2 days…then show a table describing the resulting colony descriptions).  As always, you need to show drawings, magnification (for microscopic observations), and put results in a table when appropriate.  Each set of results should be placed immediately after the brief procedure description and should be clearly labeled with a heading (ex. Gram Stain).  You must include ALL results obtained with your unknown organism (including Ex. 13-16).


Discussion…  This should consist of several well-written paragraphs that include an analysis, interpretation and evaluation of each set of results, explaining why the test/procedure was done and what knowledge was gained from it.  At each step, you should describe which organisms can be included or eliminated (for example “Since unknown #1 was identified as a Gram positive coccus, all Gram negative cocci and Gram positive rods were eliminated”).  In particular, be sure to describe if your test/procedure will help you distinguish between two similar organisms (for example Salmonella vs Proteus).  If any test results were ambiguous, discuss those problems here and state any possible sources of error.  This section should describe how you arrived at the identity of your unknown by tracing the path you followed in the appropriate flowchart.  Please include a copy of this flowchart and highlight the path that leads to your unknown.  The final paragraph of the discussion should include any additional information about your unknown such as where it is normally found, any diseases it causes and other interesting facts you have learned from outside reading.


Conclusion…”bullet points” should summarize the main results about your unknown and state the genus name of your unknown (ex. Proteus) and species name if you know it (ex. Staphylococcus aureus).


References…should be included at the end of this report (Bergey’s Manual of Determinative Bacteriology is very useful, other textbooks or online sources may also be used) and must be cited by number within the body of the text when appropriate.  Using MLA format, list at least 2-3 references that you used.


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Bacterial Unknown Lab Report

Purpose: The purpose of this experiment is to demonstrate the comprehension of the lab techniques used throughout the semester and apply those methods in determining the identification of unknown number fourteen. Also, an in-depth explanation of the tests performed as well as the practices used, will enable in the assistance of clarifying any uncertainty that may occur.


Test 1: Results of Gram Positive Unknown


TEST MEDIA/Reagents Observations Results Classifications
Gram Stain Crystal Violet, Gram’s Iodine, Ethyl Alcohol, Safranin Cocci clusters, non-motile, catalase positive, factitive anaerobe, Grape like Positive (+) Gram Positive Clusters
Catalase Hydrogen Peroxide Bubbling, fizzing Positive (+) Gram positive bacteria has catalase enzyme
Coagulase Slide Coagulase No change Negative (-) Does no react with coagulase
Urea Urea Broth Tube, Urea Slant No color change; remained yellow Negative (-) Gram positive bacteria unable to produce urease


1.) When the Gram Staining experiment took place, a clean glass slide with a small drop of H20 was first obtained. Then, with a sterile inoculating loop, the unknown bacterium was smeared onto the surface of the glass slide. After the unknown was spread on the slide, a Bunsen burner was then used to heat fix the bacterium to the surface of the slide. Next, a microscope, with the assistance of immersion oil, was then used to observe and classify the bacterium. The results we small “grape like” cluster of Gram positive bacteria. The observation can be seen below (e.g., Figure 1) as the results from the aforementioned experiment.

(Ex. Figure 1)

X1000 TM

2.) When preforming the Catalase experiment a clean glass slide whipped with water was obtained, and then dried with bibulous paper and finally air-dried. Next, a drop of hydrogen peroxide was placed in the center of the slide. Then, with a sterilized inoculating loop, the test bacteria were transferred to the drop on the glass slide. The results can be observed in (Figure 2).

(Ex. Figure 2)

3.) In the next experiment, a clean glass slide was divided into two sides using a black marker. The two small drops of distilled H2O were situated on both divided slides of the slide. Next, a small amount of the unknown bacterium was gathered using a sterilized inoculating loop and then placed into the mixture. The results inconclusive as shown in (Figure 3).

(Ex. Figure 3)

4.) When undergoing the urea test, a sterile urea test tube was obtained. Then, after getting a sterilized inoculation loop, the urea broth was inoculated with the unknown culture. Next, the inoculate was placed into an incubator for twenty-four to forty-eight hours at thirty-seven degrees Celsius. After the incubation period was over, a generous amount of the unknown organism was gathered and streaked in a zig-zag fashion onto the slanted medium. After being incubated for forty-eight hours at thirty-seven degrees Celsius the results were negative as seen in (Figure 4)

(Ex. Figure 4)




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