Review Figure 6.25 and Table 9.5 of Microbiology.
Access the “Identifying Bacteria” multimedia scenario (http://www.microbelibrary.org/microbelibrary/files/ccImages/Articleimages/shoeb/api20.html) to gain an understanding of the processes involved with identifying and classifying bacteria.
Complete Appendix B located on the student website to classify bacteria and identify a strain of bacteria responsible for a simulated food poisoning outbreak.
University of Phoenix Material
Appendix B – Identifying Bacteria
Bacteria identification is accomplished in a number of ways. Two common tools microbiologists use to identify unknown bacteria include dichotomous key and biochemical tests. The dichotomous key is useful when a microbiologist only needs to know which group an unknown microbe belongs to on a general level. When a microbiologist needs to identify a specific bacterium, biochemical tests are used.
PART ONE: GENERAL BACTERIA IDENTIFICATION
Review the dichotomous key in Figure A, the bacterial shapes in Figure B, and the Gram stain information below. You will use all three to determine to which major group unknown bacteria belong.
| Figure A:A dichotomous key for classifying major groups of bacteria.
[Figure 9.4 in Microbiology text] |
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Gram Stain Results:
Purple = Gram positive
Red = Gram negative
Neither purple nor red = No cell wall (neither Gram positive nor Gram negative)
Review Figure C on the following page. Use Figure C to identify the type of arrangement displayed by the unknown bacteria. Read through the Sample Identification on the following page for an example of how to identify bacterial groups and arrangements using Figures A, B, C, and the Gram stain results.
| Figure C: Arrangement of Bacteria | |
| Rods and Clubs | |
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Single
Strepto- Cording
Snapping
Palisades
Chinese Letters |
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| Cocci | |
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Single
Diplo- Tetrad Sarcinae Staphylo- Strepto-
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Sample Identification
After performing a Gram stain, you observe the following under a microscope:
(Cells are stained red.)
- Begin with item 1 on the dichotomous key (Figure A). Because the organisms are red, they are not Gram-positive. According to the key, continue to item 3.
- Because the organism is red (not clear or another color), it is indeed Gram-negative according to item 3. The key directs you to item 5.
- Consider the shape of individual cells for item 5. According to Figure B, the shape type is closest to spherical. (Note: spherical is circular.)
- The bacteria belong to the Gram-negative cocci group.
- Now use Figure C to describe arrangement of bacteria. (The bacteria are not rod- or club-shaped, so focus on the cocci arrangements.) Identify the arrangement that is most prominent.
- The bacteria are arranged in a diplo- fashion.
- Enter the group and arrangement in the table.
Application
Use Figures A, B, C, and Gram stain results to identify group and arrangement of bacteria. Continue to Part Two after completing the table.
