Serratia marcescens
Kayla Buchholz

Serratia marcescens is a Gram negative, bacillus shaped bacteria that belongs to the family Enterobacteriaceae. In 1819, Bartolomeo Bizio, an Italian pharmacist from Padua, discovered S. marcescens. Bizio identified the bacterium as the cause of the miraculous bloody discoloration of cornmeal mush, or polenta. He named Serratia in honor of the Italian physicist Serratia who invented the steamboat, and named marcescens from the Latin word for decaying because the bloody coloration quickly disappeared. Key characteristics of S. marcescens include the production of Dnase, lipase and gelatinase, and it is oxidase negative. These bacteria grow well on standard media and produce a red to dark pink pigment that aids in identification. 1

In the early to mid 1900s, S. marcescens was frequently used by physicians as biological marker for studying transmission of microorganisms because it was believed to be a harmless bacterium and was easy to track because of it blood red color. In fact, teachers and scientists commonly used S. marcescens in experiments of microbial transmission and to demonstrate the importance of hand washing. For instance, it was used in the “handshaking experiment” in which one person dipped their hands in S. marcescens broth and then would shake the hands of another person, who would shake hands with another person, etc . Moreover, in 1951 and 1952 the US Army conducted the experiment “Operation Sea Spray” in which S. marcescens was used to study how wind currents carried biological weapons. In this experiment, balloons were filled with the bacterium and then burst over San Fransisco. However, shortly after the study area doctors noticed a significant increase in the cases of pneumonia and urinary tract infections. Since the 1960’s S. marcescens has been classified as an opportunistic human pathogen. 2

S. marcescens tends to colonize the respiratory and urinary tracts of adults in hospitals. In adult patients, it is responsible for 2% of nosocomial infections of the blood stream, lower respiratory tract, urinary tract, surgical wounds, skin and soft tissues. In pediatric wards there have been outbreaks of S. marcescens meningitis, wound infections, and arthritis. Moreover, in people addicted to heroin S. marcescens has caused endocarditis and osteomyelitis; in these patients, mortality is very high. For those patients with nosocomial bloodstream infections, crude mortality is 26%. 2

In urinary tract infections, approximately 30-50% of the patients are asymptomatic. However, when symptoms are present they include: fever, frequent urination, dysuria, pyuria, or pain upon urination. In 90% of urinary infection cases, the patients had a recent history or instrumentation of the urinary tract. Risk factors for infection are diabetes mellitus, urinary tract obstruction, and renal failure. 2

Patients with respiratory tract infection are usually infected with S. marcescenss following instrumentation, such as ventilation or bronchoscopy, especially in patients with chronic obstructive pulmonary disease. Development of pneumonia is rare. 2

Meningitis or cerebral abscesses caused by S. marcescens can occur in premature children and neonates with prior sepsis or after a head surgery, neurosurgery, or lumbar puncture. Symptoms include those of gram-negative meningitis: headache, fever, vomiting, stupor, and coma. 2

The primary medical treatment for patients with S. marcescens infections is antibiotic therapy. S. marcescens is resistant to ampicillin, macrolides, and first-generation cephalosporins. Treatment for the bacterium includes the use of an antipseudomonal beta-lactum and an aminoglycoside. Amikacin works against most strains of S. marcescens, but there are reports of growing resistance to gentamicin and tobramicin. Most strains of S. marcescens are susceptible to quinolones as well. Antibiotic therapy should be based upon the results of susceptibility testing because there are strains that are multiresistant. 2

To identify the possible sources of infection for a toddler withS. marcescens, several swabs of possible areas of contamination where taken. These areas include: old and new saline solution, vinegar solution, rinse solution, solution canister, humidifier cup and tubing, kangaroo bag, milk container, tap water from well, mist collar, and nose soak solution. These swabs were streaked onto brain-heart infusion media and allowed to grow at 37 °C. Because S. marcescens are pigmented pink to red, colonies that were pink were isolated and streaked on new plates. The plates from the rinse solution and humidifier cup were both contaminated with pink colonies. A plate from each of the isolated colonies was incubated at 37 C and at room temperature. Colonies from both areas remained a light pink color, and did not turn the characteristic blood red color of S. marcescens. The bacteria from the isolated colonies were looked at under a bright microscope. The bacteria from both isolates were identified to be cocci, not bacillus like S. marcescens. Therefore, none of the areas tested as possible sources of contamination were positive for S. marcescenss.

“M72-2 Wound: Serratia marcescens”, ,
August 1997
“Serratia”, eMedicine,, March 18, 2004
“The Miracle Microbe: Serratia marcescens”, Microbe Zoo,
4“Serratia marcescens”, Schenectady County Community College,



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