Bacterial Genus Level Identification Key

1.  Gram Identity

            Gram Positive                                                                                                   2

            Gram Negative                                                                                                 9

2.  Cellular Morphology

            Coccus shaped (round)                                                                                     3

            Bacillus shaped (rod)                                                                                        6

3.  Catalase

            Catalase Positive                                                                                               4

            Catalase Negative                                                                                             5

4.  Oxygen Requirement

            Obligate Aerobe                                                           Micrococcus sp.

            Facultative Anaerobe                                                    Staphylococcus sp.

5.  Growth at 10 ºC

            Positive Growth                                                            Lactococcus sp.

            Negative Growth                                                          Streptococcus sp.

6.  Acid-Fast Stain

            Acid-Fast Positive                                                        Mycobacterium sp.

            Acid-Fast Negative                                                                                           7

7.  Aerial Filament Formation

            Positive                                                                        Streptomyces sp.

            Negative                                                                                                           8

8.  Endospore Production

            Endospores Produced                                                  Bacillus sp.

            Endospores Not Produced                                           Lactobacillus sp.

9.  Cellular Morphology

            Coccus/Coccobacillus shaped (round)                                                              10

            Bacillus shaped (rod)                                                                                        11       

10.  Oxidase Enzyme

            Oxidase Positive                                                           Alcaligenes sp.

            Oxidase Negative                                                         Actinobacter sp.

11.  Glucose Fermentation                                                                                           

            Glucose Not Fermented                                                                                    12

            Glucose Fermented                                                                                           14

12.  Pigmented Colonies

            Pink Colonies                                                               Roseomonas sp.

            Not Pink Colonies                                                                                            13

13.  Glucose Oxidized

            Positive                                                                        Pseudomonas sp.

            Negative                                                                       Brevundimonas sp.

14.  Indole Production

            Positive                                                                                                            15

            Negative                                                                                                           16 

15.  Lactose Fermentation

            Positive                                                                        Escherichia sp.

            Negative                                                                       Providencia sp.

16.  Pigmented Colonies

            Not Red                                                                                                            17

            Red                                                                              Serratia sp.

17.  Hydrogen Sulfide Production

            Positive                                                                        Citrobacter sp.

            Negative                                                                       Enterobacter sp.                                                                    

This is a key written in a different fashion.  The idea is the same as those keys that we have looked at in class, simply in a more compact and typing-friendly format.  Follow the outline down through to a genus level identification.  Later we will be looking at a phenotype matrix for the different genera so that you will be able to narrow the identification down to species level.

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Last Updated 6/14/2007