Biol 251 - Microbiology Lab

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Media & Biochemical Tests

You will be using a wide variety of media and biochemical tests to isolate and identify your unknown organisms. Your text has a good section on enrichment, selective, and differential media. Please review it before getting started. You are only working with a small subset of the available media and tests. It is enough however to give you a good idea of the problem solving that goes on behind the scenes to support patient care. The information provided on these pages was derived from the DIFCO Manual of media which is also available in the lab.

The media and test are arranged in alphabetical order. Refer to the information on each group of organisms to find out which media and tests are appropriate for that group.

Read the directions carefully. You must pay close attention to the conditions of the tests and media to avoid erroneous results.

Things to watch for include:

  • type of media you pull your sample from (enrichment or selective)
  • mixed or pure cultures for inoculation
  • type of inoculation - one or more colonies, needle prick from center or whole colony, light or heavy innoculation
  • application - do you stab, streak or smear the plate or tube
  • length,temperature, and atmosphere for incubation - some tests run for longer times if you get a negative result in 24 hours, others need to run for 4-5 days, others must be read at 24 hours because the colors change with storage

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