Serratia marcescens

Serratia marcescens is a species of Gram-negative, rod-shaped bacterium in the family Enterobacteriaceae. S. marcescens is involved in nosocomial infections particularly catheter-associated bacteremia. It is commonly found in respiratory and urinarty tracts of hospitalized adults and often in the gastrointestinal system of children.

It is commonly found growing in bathrooms due to its preference for damp conditions. It manifests as a pink discoloration and a slimy film feeding off phosphorus-containing materials or fatty substances such as soap and shampoo residue. Complete eradication of an established organism is often difficult but can be accomplished by application of a bleach-based disinfectant. Rinsing and drying surfaces can also prevent the establishment of the bacteria by removing its food source and making the environment less hospitable.

It is also found in dirt, supposedly “sterile” places, and the subgingival biofilm of teeth. Due to this it can cause extrinsic staining of the teeth. It is a motile organism and can grow in temperatures ranging from 5″“40°C and in pH levels from 5 to 9. It is different from other Gram-negative bacteria by its ability to perform casein hyrdrolysis. Citrate degradation produces carbon. Thus it can rely on citrate as a carbon source.

Through a methyl red test one can determine if a microorganism performs mixed acid fermentation. S. marcescens results in a negative test. It can also be tested by seeing how capable of producing lactic acid via oxidative and fermentative metabolism.

It can cause infection in the urinary tract, respiratory tract, wounds, and the eye where it may cause conjunctivitis, keratitis, endophthalmitis, and tear duct infections. It can also cause endocarditis, ostemyelitis, pneumonia, and meningitis. Due to R-factors, a plasmid that carry genes that encode resistance, many strains are resistant to several antibiotics.

Infections are common in Drosophila research laboratories where it manifests as a pink discoloration or plaque in or on larvae, pupae, or starch and sugar-based food.

It was first discovered in 1819 by Venetian pharmacist Bartolomeo Bizio when it was found to be the cause of an episode of blood-red discoloration of polenta in the city of Padua. He later named the organism in honer of Serafino Serrati. It was mistakenly believed to be non-pathogenic up until the 1950s. It has been used as a stimulant in biological warfare tests by the United States Military.

It has steadily increased in the number of human infections since 1950. It also contaminated an influenza vaccine produce by Chiron Corporation in 2004.