S. marcescens (bacillus), motile organism and can grow in temperatures ranging from 5–40°C and in pH levels ranging from 5 to 9. S. marcescens is differentiated from other Gram-negative bacteria, as it is able to perform casein hydrolysis. Performing casein hydrolysis allows for S. marcescens to produce extracellular metalloproteases which are believed to function in cell-to-extracellular matrix interactions. S. marcescens also exhibits tryptophan- and citrate-degradation. One of the end products of tryptophan degradation is pyruvic acid, which is then incorporated into different metabolic processes of S. marcescens. A final product of citrate degradation is carbon. Thus, S. marcescens can rely on citrate as a carbon source. In identifying the organism one may also perform a methyl red test, which determines if a microorganism performs mixed-acid fermentation. S. marcescens results in a negative test. Another determination of S. marcescens is its capability to produce lactic acid via oxidative and fermentative metabolism. Therefore, it is said that S. marcescens is lactose O/F+.
Due to its ubiquitous presence in the environment, and its preference for damp conditions, S. marcescens is commonly found growing in bathrooms (especially on tile grout), where it manifests as a pink discoloration. Once established, complete eradication of the organism is often difficult, but can be accomplished by application of a bleach-based disinfectant. S. marcescens may also be found in environments such as dirt, supposedly "sterile" places, and the subgingival biofilm of teeth. Due to this, and the fact that S. marcescens produces a reddish-orange pigment called prodigiosin, S. marcescens may cause extrinsic staining of the teeth. The biochemical pathway illustrating the production of prodigiosin by S. marcescens is unknown except for the final two steps. In these steps, a monopyrrole (MAD) and a bipyrrole (MBC) undergo a condensation reaction by way of a condensing enzyme to ultimately form the tripyrrole pigment, prodigiosin.
In Drosophila research laboratories, infection with S. marcescens is common. It manifests itself as a pink discolouration or plaque in or on larvae, pupae, or the usually starch and sugar-based food (especially when improperly prepared).
Since 1950, S. marcescens has steadily increased as a cause of human infection, with many strains resistant to multiple antibiotics. The first indications of problems with the influenza vaccine produced by Chiron Corporation in 2004 involved S. marcescens contamination.
Because of its red pigmentation, caused by expression of the pigment prodigiosin, and its ability to grow on bread, S. marcescens has been evoked as a naturalistic explanation of Medieval accounts of the "miraculous" appearance of blood on the Eucharist that led to Pope Urban IV instituting the Feast of Corpus Christi in 1264. This followed celebration of a Mass at Bolsena in 1263, led by a Bohemian priest who had doubts concerning transubstantiation, or the turning of bread and wine into the Body and Blood of Christ during the Mass. During the Mass, the Eucharist appeared to bleed and each time the priest wiped away the blood, more would appear. While it is possible that Serratia could generate a single appearance of red pigment, it is unclear how it could have generated more pigment after each wiping, leaving this proposed explanation open to doubt. This event is celebrated in a fresco in the Apostolic Palace in the Vatican City, painted by Raphael.
In early 2008 the FDA issued a nationwide recall of one lot of Pre-Filled Heparin Lock Flush Solution USP . The heparin IV flush syringes had been found to be contaminated with Serratia marcescens, which resulted in patient infections. The CDC confirmed growth of Serratia marcescens from several unopened syringes of this product.
9. Brown, Alfred E (2007). Benson's Microbiological Applications.