Following this exercise the student should be able to:
- Explain key characteristics in differentiating prokaryotes
- Interpret flow charts for identification
- Create flow charts for identification
Criteria for Classification of Prokaryotes
Cultural
Morphology
Microscopic Morphology
Cellular
Components
Growth Characteristics
Metabolic Pathways
Molecular
Genetics
Location in Broth
Cell Shape
Cell Wall
Atmospheric requirements
Carbon requirements
DNA base
ratio
Colony Appearance
Cell Size
Gram Stain
pH tolerance
Nitrogen
requirements
DNA
sequence
Pigmentation
Arrangement
Capsule
Temperature requirements
Sulfur
requirements
RNA
sequence
Internal Structures
Symbiotic lifestyle Fermentation
Probes
Accessory
Structures
Antibiotic sensitivity Respiration
PCR
End Products
Many different characteristics are used to identify bacteria. Identification charts (the green chart for Enterobacteriaceae) are difficult to follow. As a result microbiologists often depend upon flow charts to arrive at a preliminary identification for an organism. Flow charts are created from known results concerning bacteria. When unknown bacteria are subjected to a battery of tests the flow chart can help direct and minimize the investment of time, energy and media.
Here is a simple flow chart. An unknown bacteria is Gram stained and then a catalase test is done, followed by incubation on an MSA plate.
If the organism is a Gram positive coccus, catalase +, MSA growth with a yellow reaction - what is the identity of the organism?
Go back to lab 5. Using the data on the table with the results, fill in the following flow chart by placing the names of known results for bacteria in the boxes. (Place Staphylococcus aureus, Staph. epidermidis , E.coli, and Proteus vulgaris in the appropriate boxes.)
Now determine the identity of the following bacteria identified from the urine of an ICU patient that grows on EMB and produces a color change indicating lactose fermentation.
The flow chart is no good if the appropriate organisms are not included. Another important factor is that you must flow down the chart, you can not skip to individual tests.
More practice - Look at the flow chart (dichotomous key) on page 121 in the test. Using this chart answer the critical thinking question on page 122 of the text. Explain your answer.
Bakersfield College | Kern Community College District |
Janet Fulks
1801 Panorama Dr. - Bakersfield, CA 93305 - (661)395-4011
Date last updated
08/27/2007
ŠJanet Fulks