- Serratia marcescens. 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 30 C, but do not do so at 37o C. This is an example of temperature-regulated phenotypic expression.
Serratia marcescens colonies
