Selective and Differential Media Practice
Review Biochemicals for Unknown Identification.pptx and your Lab Manual to complete the following table.
Media What type of microorganism
grows on this agar? (i.e. Gram
positive, Gram negative,
halophile) What type of microorganism is
inhibited on this agar? (i.e. Gram
positive, Gram negative,
halophile) How do fermenters appear? (Remember non-fermenters will appear colorless or media will not change color)
Phenylethyl alcohol agar (PEA) N/A
Mannitol salt agar (MSA)
MacConkey agar
Eosin-Methylene Blue agar (EMB)
Practice Unknown: ___ E. coli ___________
In this lab, you will work independently to record the data for various biochemical tests for your practice unknown. Note that the practice unknown biochemical tests are the same identification tests that will be performed on the graded unknown.
Prior to beginning this lab worksheet, please review the Biochemicals for Unknown Identification.pptx presentation.
Prior to beginning the data interpretation portion of this worksheet, please review the selective and differential media module available through Michigan State University: http://learn.chm.msu.edu/vibl/content/differential.html.
Complete the following data tables with test observations and conclusions from experiments performed on your microbial unknown. Please use complete sentences; dont just state positive or negative for the conclusions or you will be marked off. Note: When filling out an observation, describe what you see (i.e. lactose fermentation media has turned yellow and there is air present in the inverted Durham tube). When filling out a conclusion, describe what you can learn from your observation (i.e. the unknown is capable of fermenting lactose to an acid and a gas).
Figure 1a (left). Cultural characteristics of Escherichia coli grown on TSA plate (use this image and p. 57-66 of your lab manual to complete the 4 rows shown on this page). Note that elevation has been filled out for you.
Figure 1b (right). Gram stain of Escherichia coli (use this image to complete the last two rows below on the next page).
Test Condition Observation Conclusions
Colony pigmentation on TSA plate N/A
Whole colony shape on TSA plate N/A
Colony elevation on TSA plate Slightly raised N/A
Colony margin on TSA plate N/A
Gram Stain Reaction (as viewed under oil immersion lens) (Color?) (Gram-positive or Gram-negative?)
Cell Morphology (as viewed under oil immersion lens) (Shape? Arrangement?) Remember to list both! N/A
Please use the following results (Figures 3-6) to fill out the table shown on page 8:
Figure 2. Test result for PEA agar for Escherichia coli.
2
Figure 3. Test result of Escherichia coli on Mannitol salt agar
Mannitol salt review: https://youtu.be/kG1_Tf5Vpc0
Figure 4. Test result of Escherichia coli on MacConkey agar.
MacConkey agar review: https://youtu.be/yInQ9jApAlU
Figure 5. Test result of Escherichia coli on EMB agar.
EMB agar review: https://www.youtube.com/watch?v=y4IJoMPZxk8
Test Condition Observation Conclusions
Phenylethyl Alcohol Agar Growth on plate? Gram positive or Gram negative?
Mannitol Salt Agar (Growth on plate? Color of colonies? Color of plate?) (Halophile or non-halophile? If you had growth: is the microorganism a mannitol fermenter?)
MacConkey Agar (Growth on plate? Color of colonies? Color of plate) (Gram positive or Gram negative? If you had growth, is the microorganism a lactose fermenter?)
Eosin Methylene Blue (EMB) Agar (Growth on plate? Color of colonies? Color of plate?) (Gram positive or Gram negative? If you had growth, is the microorganism a lactose fermenter?)
Please use the following test results for the table shown below.
For more information on the amylase test watch the following video: https://youtu.be/zFhMbXSgve8
Figure 6. Amylase test result for Escherichia coli
Test Condition Observation Conclusions
Presence of Amylase
-Starch plate
