|S. marcescens on an XLD agar plate.|
Serratia marcescens is a species of Gram-negative, rod-shaped bacterium in the family Enterobacteriaceae. A human pathogen, S. marcescens is involved in nosocomial infections, particularly catheter-associated bacteremia, urinary tract infections and wound infections, and is responsible for 1.4% of nosocomial bacteremia cases in the United States. It is commonly found in the respiratory and urinary tracts of hospitalized adults and in the gastrointestinal system of children. Serratia may be correctly pronounced Ser-ra-shia (common) or Ser-rah-tee-a.
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, shower corners, toilet water line, and basin), where it manifests as a pink discoloration and slimy film feeding off phosphorus-containing materials or fatty substances such as soap and shampoo residue.
Once established, complete eradication of the organism is often difficult, but can be accomplished by application of a bleach-based disinfectant. Rinsing and drying surfaces after use can also prevent the establishment of the bacterium by removing its food source and making the environment less hospitable.
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 tripyrrole 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 prodigiosin.
S. marcescens is a motile organism and can grow in temperatures ranging from 5–40°C and in pH levels ranging from 5 to 9. It is differentiated from other Gram-negative bacteria by its ability to perform casein hydrolysis, which allows it to produce extracellular metalloproteinases 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 lactic acid O/F+.
|Methyl Red||>70% -|
|Hydrogen sulfide production||-|
|Urea hydrolysis||>70% -|
|Gelatin hydrolysis, 22 C||+|
|Acid from lactose||-|
|Acid from glucose||+|
|Acid from maltose||+|
|Acid from mannitol||+|
|Acid from sucrose||+|
|Nitrate reduction||+ (to nitrite)|
|Deoxyribonuclease, 25 C||+|
|Pigment||some biovars produce red|
|Catalase production (24h)||+|
In humans, S. marcescens can cause infection in several sites, including the urinary tract, respiratory tract, wounds, and the eye, where it may cause conjunctivitis, keratitis, endophthalmitis, and tear duct infections. It is also a rare cause of endocarditis and osteomyelitis (particularly in people who use intravenous drugs recreationally), pneumonia, and meningitis. Most S. marcescens strains are resistant to several antibiotics because of the presence of R-factors, which are a type of plasmid that carry one or more genes that encode resistance; all are considered intrinsically resistant to ampicillin, macrolides, and first-generation cephalosporins (such as cephalexin).
In research laboratories employing Drosophila fruit flies, infection of them with S. marcescens is common. It manifests as a pink discolouration or plaque in or on larvae, pupae, or the usually starch and sugar-based food (especially when improperly prepared).
Possible role in medieval miracles 
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 Serratia possibly 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.
Serratia marcescens was discovered in 1819 by Venetian pharmacist Bartolomeo Bizio, as the cause of an episode of blood-red discoloration of polenta in the city of Padua. Bizio named the organism four years later in honor of Serafino Serrati, a physicist who developed an early steamboat; the epithet marcescens (Latin for "decaying") was chosen because of the pigment's rapid deterioration (Bizio's observations led him to believe that the organism decayed into a mucilage-like substance upon reaching maturity). Serratia was later renamed Monas prodigiosus and Bacillus prodigiosus before Bizio's original name was restored in the 1920s.
Role in bio-warfare testing 
Until the 1950s, S. marcescens was erroneously believed to be a nonpathogenic "saprophyte", and its reddish coloration was used in school experiments to track infections. During the Cold War, it was used as a simulant in biological warfare testing by the U.S. military which studied it in field tests as a substitute for the tularemia bacterium, which was being weaponized at the time. On September 26 and 27, 1950, the U.S. Navy conducted a secret experiment named "Operation Sea-Spray" in which some S. marcescens was released by bursting balloons of it over urban areas of the San Francisco Bay Area in California. Although the Navy later claimed the bacteria were harmless, beginning on September 29, 11 patients at a local hospital developed very rare, serious urinary tract infections, and one of these individuals, Edward J. Nevin, died. Cases of pneumonia in San Francisco also increased after S. marcescens was released., (That the simulant bacteria caused these infections and death has never been conclusively established. Nevin's son and grandson lost a lawsuit that they brought against the government between 1981 and 1983.) The bacterium was also combined with phenol and an anthrax simulant and sprayed across south Dorset by US and UK military scientists as part of the DICE trials which ran from 1971 to 1975.
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.
Contaminated injectables 
In early 2008, the U.S. Food and Drug Administration (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 S. marcescens, which resulted in patient infections. The Centers for Disease Control and Prevention (CDC) confirmed growth of S. marcescens from several unopened syringes of this product.
S. marcescens has also been linked to 19 cases in Alabama hospitals in 2011, including ten deaths. All of the patients involved were receiving total parenteral nutrition at the time, and this is being investigated as a possible source of the outbreak.
- Hejazi A, Falkiner FR (1997). "Serratia marcescens". J Med Microbiol 46 (11): 903–12. doi:10.1099/00222615-46-11-903. PMID 9368530.
- Auwaerter P (October 8, 2007). "Serratia species". Point-of-Care Information Technology ABX Guide. Johns Hopkins University. Retrieved on December 13, 2008. Freely available with registration.
- Anía BJ (October 1, 2008). "Serratia: Overview". eMedicine. WebMD. Retrieved on December 13, 2008.
- [dead link]
- Bergey's Manuals of Determinative Bacteriology, by John G. Holt, 9th ed. Lippincott Williams & Wilkins, January 15, 1994. pp. 217
- "Serratia Marcescens seton implant infection & orbital cellulitis". EyeRounds.org. Retrieved 2006-04-06.
- Patterson KL, Porter JW, Ritchie KB, et al. (June 2002). "The etiology of white pox, a lethal disease of the Caribbean elkhorn coral, Acropora palmata". Proc Natl Acad Sci USA 99 (13): 8725–30. doi:10.1073/pnas.092260099. PMC 124366. PMID 12077296.
- Bennett JW, Bentley R (2000). Seeing red: The story of prodigiosin. "Advances in Applied Microbiology Volume 47". Adv Appl Microbiol. Advances in Applied Microbiology 47: 1–32. doi:10.1016/S0065-2164(00)47000-0. ISBN 978-0-12-002647-0. PMID 12876793.
- "The Mass at Bolsena by Raphael". Vatican Museums. Retrieved 2006-05-03.
- Sehdev PS, Donnenberg MS (October 1999). "Arcanum: The 19th-century Italian pharmacist pictured here was the first to characterize what are now known to be bacteria of the genus Serratia". Clin Infect Dis 29 (4): 770, 925. doi:10.1086/520431. PMID 10589885.
- Bizio's original report was translated into English in 1924, and published in the Journal of Bacteriology. See Merlino CP (November 1924). "Bartolomeo Bizio's Letter to the most Eminent Priest, Angelo Bellani, Concerning the Phenomenon of the Red Colored Polenta". J Bacteriol 9 (6): 527–43. PMC 379088. PMID 16559067.
- Democracy Now! | How the U.S. Government Exposed Thousands of Americans to Lethal Bacteria to Test Biological Warfare
- Cole, Leonard A. (1988). Clouds of Secrecy: The Army's Germ-Warfare Tests Over Populated Areas. (Foreword by Alan Cranston.). Totowa, New Jersey: Rowman & Littlefield. ISBN 0-8476-7579-3.
- Regis, Ed. The Biology of Doom : America's Secret Germ Warfare Project. Diane Publishing Company. ISBN 0-7567-5686-3.
- Cole, Op. cit., pp 85-104.
- Barnett, Antony (2002-04-21). "Millions were in germ war tests". The Guardian. Retrieved 2012-10-27.
- AM2 PAT, Inc. Issues Nationwide Recall of Pre-Filled Heparin Lock Flush Solution USP (5 mL in 12 mL Syringes)
- Nisbet, Robert (30 March 2011). "Drip Feeds Linked To US Hospital Deaths". Retrieved 31 March 2011.
- "CDC And ADPH Investigate Outbreak At Alabama Hospitals; Products Recalled". FDA. Retrieved 31 March 2011.