31.16: Flow Chart
- Page ID
- 165429
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- Select appropriate laboratory tests for identifying an unknown bacterium based on previous test results.
- Construct a logical and efficient flow chart that uses test outcomes to progressively narrow down possible bacterial identities.
BACKGROUND
One of the most important skills in microbiology is the ability to identify an unknown bacterium based on laboratory testing. In clinical, research, and public health settings, accurate identification of microorganisms is critical for diagnosing infections, choosing the correct treatments, tracking disease outbreaks, and conducting scientific investigations.
Because bacteria cannot be reliably identified by appearance alone, microbiologists use laboratory tests to gather clues about an organism’s identity. Some tests reveal structural features, such as the Gram stain, which divides bacteria into Gram-positive and Gram-negative groups based on differences in their cell wall. Other tests detect metabolic traits, such as the ability to ferment sugars, produce specific enzymes, or utilize certain nutrients. These biochemical tests can reveal important information about how a bacterium functions and help narrow down its identity.
However, not every test is helpful for every organism. Running every possible test on an unknown would be wasteful and slow down the identification process. Instead, microbiologists use a flow chart (a step-by-step decision-making guide that helps you choose which tests to run based on the previous result). Although not technically a metabolic test, typically, a flow chart begins with the Gram stain. Each test should separate approximately half of the possible organisms until each organism is isolated. Consistently utilizing tests that only separate one organism from the group at a time will result in more testing then necessary in order to identify the unknown.
In this exercise, you will learn how to select appropriate tests from a set of data then practice building a flow chart using a small set of organisms and sample data.
METHODS
1. Only use tests that are included in the table below.
2. Review the list of possible organisms and their test results.
3. In the space provided in the Results section below write the names of all the organisms in the Gram negative sample data table below in a row across the top of the paper.
*Remember the genus can be abbreviated but the species cannot.
4. Find a metabolic test in which approximately half of the organisms have one result, and half have a different result. Write the name of the test underneath the row of possible organisms then draw a line under the name of the test that is a little shorter than the width of the paper. Above the line add the result possibilities. Write the organisms i n a row under the correct result.
5. Continue to separate the organisms based on their test results until each organism is isolated.
Ex 31.16 FLOW CHART
NAME ______________________
EXPECTATIONS
If there are 10 possible organisms, how many tests do you think it would take to identify what organism you have?
Use the data below to build a Gram-negative flow chart in the results section.
RESULTS
Gram Negative Flow Chart:
CONCLUSIONS
Use the sample Gram-positive data above to answer the following questions.
1. What metabolic test can be used to separate B subtilis from S. epidermis other than the Citrate test?
2. What metabolic test (or tests) should not be used to separate E. faecalis from L. acidophilus, and S.
epidermis?
3. What test, other than Catalase, would be appropriate to start a flow chart with? Explain your reasoning.
4. Why do microbiologists use flowcharts when performing metabolic tests to identify an unknown
organism?