do a lab summary of minimum 300 words.
18
If we swabbed the palm of our hand, mix this into a tube of physiological saline or distilled water, streak this onto a plate of media and incubate, many colony types would grow because many different species of bacteria were present in the sample. Some of these colony types would be easily distinguishable, even by the untrained individual because of unique colors (Micrococcus & Pseudomonas), surface luster (Bacillus & Corynebacterium), shape (Proteus), or texture (Klebsiella). For other colony types, the colonial morphology would be quite similar. This is generally true of the Gram negative rods. Colony morphology must be examined closely. With practice, you will learn to see subtle differences between similar colony types. Colony morphology is an important piece of evidence used in identifying organisms, BUT you should never use it as the sole means of making the final call when you have other means of characterization. Remember this when working on your unknown.
You should find colony morphology especially helpful in distinguishing the following organisms:
*species of the genus Bacillus from other Gram positive rods
*Bacillus species one from another
*Corynebacterium xerosis from the other Gram positive rods
*Staphylococcus species from Streptococcus species
*Staphylococcus aureus from the other catalase positive Gram positive cocci
*Pseudomonas aeruginosa and Alcaligenes faecalis from the other oxidase positive Gram negative rods
*Pseudomonas aeruginosa from Alcaligenes faecalis
*Klebsiella pneumoniae from the other oxidase negative Gram negative rods
Colony morphology is commonly described using the 7 parameters listed below. You may prefer descriptors other than those listed (ex.: round instead of circular), or you may need to use additional descriptors (such as “terraced” elevation, etc.) if one provided does not accurately describe what you see.
|
| circular | irregular | rhizoid | other? | |
| Edge: | entire | lobate | serate | other? | |
| Density: | Opaque | translucent | transparent | ||
| Surface: luster | Shiny | dull | wrinkled | other? | |
| Texture: | crumbly | hard | creamy | mucoid | other? |
| Elevation: | convex | flat | raised | umbonate | other? |
| Color: |
NOTES:
* Colony morphology is not very “testable.” The purpose of this exercise is to make you aware of
differences in the appearance of colonies so you can use this as another bit of evidence in identification.
Images 14 – 38: colony morphology of each organism. See “index of images” on page vii.
