Serratia marcescens

Basic description of microbe:

• Straight rods

• Motile

• Facultatively anaerobic

• 0.5-0.8 μm in diameter and 0.9-2.0 μm in length

• Optimal temperature: 25˚C

What it looks like on the agar:

• Whole Colony                                      Round

• Margin                                                 Smooth

• Elevation                                              Umbonate

• Color*                                                 Reddish-pink pigment

* S. marcescens produces a reddish-pink pigmented color when grown at room temperature (25 ˚C).  If grown above or below room temperature, this species loses its ability to produce the pigment which explains the whitish edging around the colonies in our pictures below.

Biochemical tests: 

• Indole                                                  negative

• Simmons Citrate                                  positive

• Voges-Proskauer                                 positive

• Lysine Decarboxylase                          positive

• H₂S                                                     negative

• Urea hydrolysis                                    negative

• Catalase                                               positive

Interesting Facts:

• Occurs in human clinical specimens, soil, water, plant surfaces, and other environmental sites, digestive tract of rodents, and insects

• Prominent opportunistic pathogen for hospitalized humans, causing septicemia and urinary tract infections