Colony characteristics of bateria in Trypticase Soy Agar (TSA)

1. Bacillus subtilis :

Colonies which are dry, flat, and irregular, with lobate margins.

2. Pseudomonas aeruginosa

This Gram negative rod forms mucoid colonies with umbonate elevation. Some strains produce a diffusible green pigment and a distinctive fruity odour.

3. Staphylococcus aureus

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

4. Mycobacterium smegmatis

The waxy appearance of Acid-fast bacterium.

5. Escherichia coli

This Gram negative rod forms shiny, mucoid colonies which have entire margins and are slightly raised. Older colonies have entire margins and are slightly raised. Older colonies often have a darker centre.

6. Serratia marcescens

These gram negative rods produce mucoid colonies which have entire margins and umbonate elevation. 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 30 degree centigrade, but do not do so at 37 degree Centigrade. This is an example of temperature-regulated phenotypic expression.

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