MICROBIOLOGY LAB MANUAL
Lab 6 - Prokaryotic Identification and Flow Charts
Following this exercise the student should be able to:
1. Explain key characteristics in differentiating prokaryotes
2. Interpret flow charts for identification
3. Create flow charts for identification
On the chart below briefly describe what or how these identification characteristics are
used to make conclusions. (See the first box for a sample answer)
Cultural
Morphology
Microscopic
Morphology
Cellular
Components
Growth
Characteristics
Metabolic
Pathways
Molecular
Genetics
Cell Shape
Cell Wall
pH tolerance
Carbon
requirements
DNA base
ratio
Colony
Appearance
Arrangement
Gram Stain
Temperature
requirements
End Products
Fermentation/
Respiration
DNA
sequence
Pigmentation
Internal
Structures
Capsule
Sensitivity to
chemicals
Sugar needs
RNA
sequence
Accessory
Structures
DNA/Plasmids
Antibiotic
sensitivity
Enzymes
PCR/Probes
Page
1
Location in
Broth
Displays aerobic
optimums
Dr Janet Fulks
Bakersfield College
August 2010
MICROBIOLOGY LAB MANUAL
Criteria for Classification of Prokaryotes
Many different characteristics are used to identify bacteria. Identification charts/tables
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. These flow charts are called dichotomous keys.
Dr Janet Fulks
Bakersfield College
August 2010
Page
Do you recognize the questions as you flow down the chart? What a question that could be
asked at the Eukaryotic box to get answers that bifurcate (divide into two) organisms that are
identified as algae versus those that are identified as protozoans?
Remember these are presumptive flow charts – there are often answers that do not fit nicely
into the flow, which would then require more information. Can you think of an organism that
would not be classified cleanly by this flow chart from the kingdom Protista?
2
Each step in the flow chart asks a question indicated by the information in the square. It is
helpful to ask a yes no question and to always place the yes or positive answer on the left and
the no or negative answer on the right.
MICROBIOLOGY LAB MANUAL
Now create a simple dichotomous key or flow chart for the Multicelled organism identification
pathway. What are the three kingdoms that will represent all multicelled organisms?
What question(s) would help divide them into those kingdoms? You may be surprised to find
that there are different ways that this flow chart can be constructed.
Page
3
When we apply this identification or decision making principle using flow charts, we are able to
identify bacteria and decide what kinds of biochemical testing to perform. Using just the tests
we have currently worked with (Gram Stain, Differential and Selective Media) we can construct
a simple flow chart.
Dr Janet Fulks
Bakersfield College
August 2010
MICROBIOLOGY LAB MANUAL
Here is a simple flow chart insert the appropriate species in the final Gram positive boxes. An
unknown bacteria is Gram stained and identified as a Gram positive coccus, in clusters - what is
the identity of the organism?
Page
4
Go back to lab 5. Using the data on the table with the results, create a flow chart on the next
page that identifies bacteria using the selective and differential nature of MSA, EMB and/or
MacConkey agar.
Dr Janet Fulks
Bakersfield College
August 2010
MICROBIOLOGY LAB MANUAL
Dr Janet Fulks
Bakersfield College
August 2010
Page
Review - Look at the flow chart (dichotomous key) in the text. Answer the
critical thinking question and explain your answer. The instructor will hand out
additional flow charts which have more detail and will be used throughout the
rest of the semester.
5
Using the key that you created determine the identity of a bacteria isolated from the urine of an
ICU patient that grows on EMB and MacConkey Agar and produces a color change indicating
lactose fermentation.
Page
6
MICROBIOLOGY LAB MANUAL
Dr Janet Fulks
Bakersfield College
August 2010