Serratia Marcescens

Serratia species are opportunistic gram-negative bacteria classified in the tribe Klebsielleae and the large family Enterobacteriaceae.

Serratia marcescens is the primary pathogenic species of Serratia. Rare reports have described disease resulting from infection with Serratia plymuthica,  Serratia liquefaciens,  Serratia rubidaea,  and Serratia odorifera.

Some strains of S marcescens are capable of producing a pigment called prodigiosin, which ranges in color from dark red to pale pink, depending on the age of the colonies. S marcescens has a predilection for growth on starchy foodstuffs, where the pigmented colonies are easily mistaken for drops of blood.

In 1819, Bartolomeo Bizio, a pharmacist from Padua, Italy, discovered and named S marcescens when he identified the bacterium as the cause of a miraculous bloody discoloration in a cornmeal mush called polenta. Bizio named Serratia in honor of an Italian physicist named Serrati, who invented the steamboat, and Bizio chose marcescens (from the Latin word for decaying) because the bloody pigment was found to deteriorate quickly.

Since 1906, physicians have used S marcescens as a biological marker for studying the transmission of microorganisms because, until the 1950s, this bacterium was generally considered a harmless saprophyte. Only since the 1960s has S marcescens been recognized as an opportunistic pathogen in humans.