30 Lab 3 - Data Analysis
After attending the practical lab, you should:
Compare the results from your blood agar plates with what is known in the literature (Section 30.1).
Compare the results of your biochemical tests with what is known in the literature (Section 30.2).
Analyse the results from the API-20E test that was performed for you (Section 30.2.1)
In lab 4, you will examine and record the results from your MacConkey and Mannitol Salt Agar plates. You should reread Section 25.1.1 and Section 25.1.2 to make sure you understand what to expect in the next lab session, and how to interpret your data.
In lab 4, you will examine and record the results from your fluid thioglycollate cultures and your anaerobically incubated plates. You should reread Section 28.1 to make sure you understand what to expect in the next lab session, and how to interpret your data.
30.1 Task 3A Data Analysis
For the controls (Enterococcus faecalis, Streptococcus pneumoniae, Streptococcus pyogenes) - does the phenotype you observed match what you would expect based on the literature?
How precisely can you identify your unknown based on your observations?
Questions to consider/discuss with your lab partners:
Are you confident in the accuracy of your results (are there any ways that your experiment could have yielded a false positive/false negative)?
What other experiments might help you to identify your unknown?
For Case Study 2 (suspected Group A Strep infection), what should the clinical microbiologist do next? What about the physician?
- Consider your aseptic technique, any other potential problems with your experiment…?
2-3. You might find it helpful to refer to your lecture notes, the UK SMIDs for these organisms, or taxonomic resources such as Bergey’s.
30.2 Task 3B and 3C Data Analysis
In the next lab session, you will be able to observe your MacConkey agar plates. You will examine the colony morphology and lactose fermentation phenotype on each plate in order to help identify your unknown. (You should look back at Section 25.1.1 if you need to review the expected phenotypes on this agar.)
You should also use the results from your oxidase and catalase tests (Task 3C), as well as the results from the API-20E experiment that was performed for you (Section 26.1), to identify your unknown.
For the controls you used in the oxidase and catalase tests - do the phenotypes you observed match what you would expect based on the literature?
For your unknown - what phenotypes did you observe, and what can you conclude from them?
Are you confident in the accuracy of your results (are there any ways that your experiment could have yielded a false positive/false negative)?
30.2.1 API-20E Data Analysis
You can download the data from the API test that was performed for you, as well as an interpretation guide, here.
Use the API test finder from BacDive to look up your unknowns. You can should also use the BacDive database to look up the expected results for the suspected pathogens that might be present in the spinach.
Are you confident in the identification of the unknowns? What other experiments could you perform that would help to precisely identify these unknowns?
Questions to consider/discuss with your lab partners:
Is there any variation observed within the API-20E test results for a given species?
What are the strengths/weaknesses of using the API-20E system to identify an unknown?
Are all isolates of the same species identical at the genomic level? Might there be some variation in test results depending on culture conditions and/or the way a given lab carries out the test? Are there any other factors that might affect the test results?
Is this method for identification precise? reproducible? technically challenging? etc.