Identification of an unknown bacterium
During this semester, you will learn different techniques used in the microbiology laboratory. In addition to simply learning how to perform different tests, each group of 2-3 students will also be assigned an unknown bacterium (numbered #1 - #5). You will perform a variety of tests on this organism throughout the semester and by the end of the semester, you should be able to identify your organism.
You will be performing tests on your unknown during labs 1, 3-5, and 7-9. I have listed the protocols for each of the tests on the course schedule and also on the lab home page in a document called identify your unknown experiments. You will need to print and perform these experiments in addition to the other experiments in the class. The other laboratories are for you to learn techniques and you will then need to take the practical exam covering these techniques. I will not collect any data for any of these experiments but you may want to keep your own notebook which will help you to perform well on the lab practicals.
All of the data that you will collect on the unknown experiments will need to be included in your lab report at the end of the semester so you will want to keep a good record of this data. However, I will NOT grade this data until the end of the semester.
You will be working as a group to perform these experiments but at the end of the semester, you will need to hand in INDIVIDUAL lab reports.
Unknown bacterial cultures
At the beginning of the semester you will be assigned an unknown organism with a number of 1-5. If you were in a normal microbiology laboratory, you would be expected to sterilely maintain stocks of this organism until you had completed all of these tests. But, based on my experience teaching this class, I believe that some students may contaminate their stock cultures. Therefore, for each laboratory that you will need your culture, you will be given a fresh stock of it. But, you will always need to use the same number. You will not be able to change during the semester.
Background
If you were to perform a forensic DNA experiment, if you only obtained data from 1 or 2 experiments, you would not be able to be completely confident on whose DNA you had. Similarly, if you only performed 1-2 experiments on your bacterium, you would not be able to determine its exact identity. But, you will perform a number of morphological, physiological and biochemical tests on your organism in the hope of trying to identify it.
Experimental protocol
Look at the lab schedule for the detailed protocols but I have listed below the labs and technique that you will perform on your unknown organism.
Lab 1: You will inoculate your unknown organism into different medias (broth, deep and slant) hand observe the growth patterns and document it with the appropriate terms. You can compare the growth to known organisms that we use in the lab or at the end of the semester, when you think you know what your organism is you can do research and see if this organism has the same growth patterns. This last statement is true for all of the tests that you will perform
Lab 3: Streak your organism on a NA agar plate and a MacConkey agar plate. Observe the growth patterns and document it with the appropriate colonial morphology terms (shape, elevation, margins and color of your colonies). You will need to use a dissecting microscope for this part of the experiment.
Lab 4 and 5: Make a smear of your organism and gram stain it. You will need to determine if your organism is gram + or gram – and what the cellular morphology is (shape and arrangement of cells).
Lab 7: You will need to determine physiological properties of your unknown (temperature, salt and oxygen requirements).
Lab 8: Determine antibiotic sensitivity of your organism
Lab 9: Perform a variety of biochemical tests on your unknown. In some instances, there may be more than one test to indicate a single property. This situation is helpful because sometimes the results are ambiguous or may need a confirmatory test performed.
Lab Report
By the end of the semester, you should have all of the data needed to write up your laboratory report. You performed the experiments as a group and should have the same data but your report should be YOUR OWN WORK. I do not want to read the same laboratory report more than one time. When you put things in your own words or look up references, it should be different than your lab partners. Also, you CANNOT copy exact what I wrote in the description of the project or in the lab protocol. Write things in YOUR OWN WORDS.
You will need to include the following sections in your lab report:
Purpose
Write in your own words why you are doing this project. What do you hope to accomplish?
Method
Describe in general terms, the different tests that you performed and what you expected to find. You do not need to write out all the experimental details. For example, you might write that you performed a gram stain to determine if the unknown organism was gram + or gram -. You do not need to write all the steps in the gram stain procedure. Another example might be that you plated the colonies and looked under the dissecting scope to determine the colony morphology. You should write what biochemical tests you performed and what media you used but you do not need to write, for example, that you added a few drops of a certain reagent to your tube.
Results
For each test performed, you need to write what the results were. You will need to include here the colony and cellular morphology and the gram reaction results. You should also include a table with the results from the physiological and biochemical tests. I have given an example of what should be included in the table below:
|
Test Performed |
Result |
Interpretation |
|
Salt concentration |
++ growth at 1% and no growth at 5 or 10% |
Bacteria is a non halophile. |
|
Thioglycollate |
Growth only at the top of deep. |
Organism is an obligate aerobe. |
|
TSI slant |
Yellow butt, red slant, no black, no bubble |
Organism ferments glucose only. Sucrose and lactose are not fermented and H2S is not produced. |
Discussion
You should write here what you determined your unknown microorganism to be. How did you decide this? You should include a flow diagram for the biochemical tests and explained how you eliminated certain organisms from your analysis.
If you had any problems in the experiments, you should explain that here. Were your results ambiguous? Explain here what you think happened.
Describe your unknown organism
This description should be added in the discussion section after you explain what your organism is. . Include primary habitat, diseases it may cause and any other interesting information to describe your organism. Use your textbook or any other MICROBIOLOGY TEXTBOOK or primary research articles. You may NOT use the Internet for any of your sources. No Wikipedia, web MD, etc. If it begins with www. you may not use it. You must also properly cite your references within the text and also have a list of references at the end of the paper.
You will find on the next few pages, a grading rubric describing how each section will be graded.
|
Criteria |
3 |
2 |
1 |
0 |
Purpose |
Student clearly explained in his/her own words what the purpose of the project was. |
X |
X |
This statement was not written by the student in his/her own words |
Methods |
The student explained all of the tests performed in his/her own words |
The student left out the description of one test or had one section that was not in his/her own words |
The student left out the description of two tests or had two sections that was not in his/her own words |
The student left out the description of three tests or more and had many sections that were not in his/her own words |
Results |
The student included all of the results for all of the tests performed in this series of experiments. |
The student left out one result from one test performed in this series of experiments. |
The student left out two results from two tests performed in this series of experiments. |
The student left out three or more results from tests performed in this series of experiments. |
Discussion |
The student clearly discussed the results in his/her own words. |
The student’s discussion lacked a few details and/or was not completely in his/her own words. |
The student’s discussion lacked many details and was not in his/her own words. |
No discussion was included. |
Description of organism |
Student clearly explained details about the organism in his/her own words. |
The description of the organism lacked a few details and/or was not in his/her own words. |
The description of the organism lacked many details and/or was not in his/her own words. |
No description of the organism was given |
|
Criteria |
3 |
2 |
1 |
0 |
Background Research/thorougness
|
Student completed much background researrch and/or put much thought into the analysis of the data. |
Student completed adequate background research and put adequate thought into the analysis of the data |
Student completed only a little background research and put very little thought into the analysis of the data. |
Student did not complete enough background research and barely thought about the data. |
|
Organization of Paper |
Paper was well organized and thorough |
The paper either lacked some organization or thoroughness |
The paper was not organized well and it was not very thorough |
The paper was completely disorganized |
|
References used |
All references were from textbooks or scientific journals. |
X |
X |
One or more references were from the Internet |
|
References cited throughout the paper |
All references were cited correctly and cited where needed. |
One reference was cited incorrectly and/or there was one section where no reference was cited. |
Two references were cited incorrectly and/or there were two sections where no references were cited. |
Three references were cited incorrectly and/or there were three or more sections where no references were cited. |
|
Reference list at the end of the paper |
All references were cited correctly. |
One reference was cited incorrectly or one mistake was made for all references. |
Two references were cited incorrectly or two mistakes were made for all references. |
Three or more references were cited incorrectly or three or more mistakes were made for all references. |
|
General writing ability |
Follows all the rules of English grammar and rarely misspells words. |
Occasionally needs grammar and spelling corrections. |
There are many misspelled words and poor grammar. |
More words are spelled incorrectly than correctly. The writing is very poor. |
Correctness |
Everything written is correct |
One thing written is incorrect |
Two things written are incorrect |
More than two things written are incorrect |
|
Something else was messed up |
3 pts |
|
|
|
This grading rubric contains 39 points. This assignment is worth 100 points. To get your final grade for this lab report, I will assign you a number of points based on this rubric, divide the number by 39 and multiply by 100.