1. Figure 7-4 Colony morphology descriptions
As microorganisms grow and divide on solid surfaces they form specific patterns of growth. Individual cells (or a few identical cells) will continue to grow and divide and form discrete units called colonies, the morphology of which is characteristic of that microbial species. An accurate description of an isolated colony can greatly aid in the identification of the microorganism. Microbiologists have developed standard words with specific meanings to describe colony form, elevation and margin. Scientists use this jargon to help accurately communicate their observations. This is a common theme in all disciplines of science. Imagine what would happen if everyone used different terminologies? There would be no effective communication between scientist. 1

2. E. coli
medium sized colonies
regular margin
convex elevation

3. Klebsiella pneumoniae
Slightly gummy/wet looking colonies
Circular
convex
entire margin

4. Bacillus subtilis.  These gram positive, sporeforming rods produce colonies which are dry, flat, and irregular, with lobate margins.

5. Pseudomonas aeruginosa
Pseudomonas aeruginosa.  This gram negative rod forms mucoid colonies with umbonate elevation.  Some strains produce a diffusable green pigment and a distinctive fruity odor.  P. aeruginosa is an opportunistic contaminant of burn injurys, wounds such as cuts and gunshot, and can cause bacterial pneumonia.  It is often nosocomial pathogen, easily transmitted by hands and invasive medical procedures.

6. Salmonella choleraesuis serovar typhimurium
Salmonella choleraesuis serovar typhimurium.  This gram negative rod is a component of the gastrointestinal tract of birds and reptiles and is an agent of gastroenteritis in humans.  It forms shiny, convex colonies with entire margins.

7. Escherichia coli.  This gram negative rod (coccobacillus) forms shiny, mucoid colonies which have entire margins and are slightly raised.  Older colonies often have a darker center.

8. Rhodospirillum rubrum
Rhodospirillum rubrum.  Pinpoint circular colonies which are convex with entire margins.  This gram negative spirillum produces a non-diffusable red pigment.

9. Micrococcus luteus.  Circular, pinhead colonies which are convex with entire margins.  This gram positive coccus produces a bright yellow, non-diffusable pigment

10. Staphylococcus aureus
Staphylococcus aureus.  Circular, pinhead colonies which are convex with entire margins. This gram positive coccus often produces colonies which have a golden-brown color.

11. Staphylococcus epidermidis
Staphylococcus epidermidis.  Circular, pinhead colonies which are convex with entire margins.  The colonies of this gram-positive coccus appear either the color of the agar, or whitish.

12. Bacillus subtilis Colonies large margin is undulate or lobate dry
with circular form
flat elevation

13. Staphylococcus aureus.
Circular
Pinhead
Convex
Entire margin
.  Circular, pinhead colonies which are convex with entire margins. This gram positive coccus often produces colonies which have a golden-brown color 13

14. Serratia marcescens Mucoid Entire margin Umbonate elevation
Red and white colonies
These gram negative rods produce mucoid colonies which have entire margins and umbonate elevation.  Note that there are both red and white colonies present on this plate.  Some strains of S. marcescens produce the red pigment prodigiosin in response to incubation at 30o C, but do not do so at 37o C.  This is an example of temperature-regulated phenotypic expression.   14