A study of the microbe, Serratia marcescens


Bacteria are a group of prokaryote organisms and the most ancient life forms on Earth, able to survive in every habitat, from deserts to freezing conditions in Antarctica. They come in a very wide range of shapes and sizes. Certain types of bacteria can cause diseases and can be lethal to the humans, animals, plants and the environment while other bacteria can be beneficial that we could not live without. (Madigan et al, 2009)

I will be writing about the bacterium Serratia marcescens, a human pathogen which has a high frequency around the world, affecting very vulnerable people, especially in hospitals.

With the help of scientific journals and textbooks, I will be talking about the history of S. marcescens, how it has played a big part in religious theology, what diseases it causes, how it is transmitted between individuals and how it can be treated, and ultimately how dangerous and important this bacterium is.

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Serratia marcescens is a bacterium, part of the Enterobacteriaceae family. It is Gram-negative, rod-shaped and a human pathogen which causes nosocomical infections, including urinary infections. It is a motile, facultative anaerobic organism and is found in soil, water and in 'sterile environments' such as hospitals (Madigan et al, 2009) It is capable of producing a dark red to pale pink pigment called prodigiosin, which can help to isolate and detect infections. This can grow on food, such as bread and throughout history, has been easily mistaken for drops of blood.

Due to this, S.marcescens has played a major role in mankind for the past 2000 years. In ancient history, when the bacteria produced the blood-red pigment on starch-based foods, the Greeks and Romans perceived this as a sign from the gods, a devine destiny. (Greenberg, 1978) The appearance of this pigment is mentioned in the Miracle of Bolsena, where in Bolsena, Italy in 1263 a priest appeared to bleed onto a small cloth upon the bread and wine rest during Mass. The manifestation of blood was seen as a miracle to confirm the Roman Catholic belief of transubstantiation, which denotes the transformation of bread and wine into the substance of the Body and Blood of Jesus Christ in the 'The Last Supper'. (Digital Learning Center for Microbial Ecology, 1999)

In the Middle Ages, the theology of transubstantiation was eventually developed into church doctrine and led to disturbing events. The S.Marcescens infection in bread was perceived as an act of blasphemy and led in the mass slaughter of Jews, who were "accused of destructive attempts against the Eucharist" (Greenberg, 1978)

Bartolomeo Bizio, a pharmacist from Padua, Italy, discovered and named S. marcescens in 1819 when he identified it as the cause of the bloody pigment in polenta. It was named Serratia after an Italian physicist named Serrati, who invented the steamboat, and marcescens from the Latin word for decaying because the pigment weakened fast. (Basilio, 2010)

Up until the mid 20th century, S. marcescens was thought to be non-pathogenic and because of it characteristic feature of red pigment production, it was used as a biological marker by scientists and in schools, in studying and tracking bacterial infections. For example, a common experiment was to demonstrate the importance of hand washing by which a person would place their hand in a beaker of S. marcescens and then shake hands with another person and so on, and the bacterium was tracked down. (Buchholz 2004)

However the perception that S. marcescens was harmless was changed. In 1951 and 1952, the US Army carried out a series of experiments to see whether US port cities could be targets for biological warfare and the effect of wind dispersal. (Buchholz, 2004) The experiment "Operation Sea Spray" was conducted in San Francisco and S. marcescens was used because it was easily tracked, due to producing red colonies on samples, and it was assumed harmless. S. marcescens particles were released over the city, exposing hundreds and thousands of people. After the exposure, there was a major increase in cases of urinary tract infections and pneumonia and one person, Edward J. Nevin died due to an S.marcescens infection that attacked his heart valves. (Tansey, 2004) Due to this incident, S. marcescens has been classified as a human pathogen.

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S. marcescens have now been recognised as important nosocomial pathogens, resulting in urinary and respiratory infections, and "responsible for endemic and epidemic infections, especially in newborns and patients submitted to invasive procedures" (Carbonell, 2003)

As an important opportunistic pathogen in neonatal and paediatric intensive care units. Raymond (2000) states that S. marcescens was responsible for 15% and 5% of all culture-positive nosocomial infections in neonatal and in paediatric, respectively and in a case control study (Foglia et al, 2007), S. marcescens was the causative pathogen in 8% of all bacterial nosocomial infections in a paediatric unit, including outbreaks of meningitis.

For urinary tract infections, most patients are asymptomatic but some patients may suffer frequent urination, pyuria, fever and in 90% of cases, patients have had recent surgery of the urinary infection (Basilio, 2010), indicating the bacterium has high resistance.

The bacterium also colonise the respiratory tract and resulting in infections of the lower respiratory, bloodstream and surgical wounds.

The bacterium infection can cause infections in the eye, such as keratitis, conjunctivitis and these can be linked by contact lens wear and previous eye surgery. (Eyeround.org, 2008)

Also, S. marcescens have known to have caused endocacarditis and osteomyelitis among people addicted to heroin. (Basilio, 2010) Around the world, the yearly incidence rate 1.03 per 100,000 populations with most outbreaks occurring in hospitals.

According to Engel et al, (2009) the 7 day and 6 month mortality rates were 5% and 37% respectively and 68% cases of S. Marcescens infection show up in males.

As S.marcescens is a nosocomial infection, it can be transmitted easily in hospitals, usually by direct contact and on unclean hospital equipment.

In 2007, a recall of Pre-Filled Heparin lock flush syringes and normal saline IV flush syringes was initiated by the U.S. Food and Drug Administration. The syringes had been contaminated with S. marcescens, which resulted in bloodstream infections in patients. There were reports of growth of S. marcescens colonies from several unopened syringes, by the Center for Disease Control. (U.S. Food and Drug Administration, 2009)

The bacterial infection was seen as a serious health consequence that could manifest to life-threatening injuries or death.

The infection can also be transmitted by unclean catheters and the use of contaminated intravenous infusions. A high outbreak of infection was traced back to contaminated intravenous magnesium sulphate distributed in the USA by a pharmacy. (Sunenshine et al, 2007)

To treat S. marcescens infection, antibiotic therapy is mostly used. S. marcescens is naturally resistant to ampicillin, and cephalosporins. According to Mlynarczyk, (2007) 92% of strains were resistant to cefotaxime, however 99% were susceptible to ceftazidime.

The bacterium can be treated with "an aminoglycoside plus an antipseudomonal beta-lactam, as the single use of a beta-lactam can select for resistant strains." (Basilio, 2010)

However, treatment should be based on results of susceptibility testing because multi-resistant strains are common.

Antibiotics used to treat S. marcescens, include levofloxacin, cefepime, ertapenem, and aztreonam.

For further prevention of the infection, recommendations include, in hospitals, avoid re-using intravenous lines and make sure they are removed as soon as possible. Make sure that hospital employees clean their hands thoroughly and hospital equipment, including surgical tools, are always cleaned between use and kept sterile.

S. marcescens is a bacterium that is highly pathogenic to humans if left untreated and can cause considerable damage. It has affected mankind for thousands of years, due to its characteristics, being indirectly mentioned in holy books and transcripts, with noted scholars linking its activities to acts of divination. It can be easily transmitted between individuals which adds to the lethality of the infection and it mostly infects the most vulnerable people, patients in hospitals, including toddlers and new-born babies.

S. marcescens has proven to be resistant to several antibiotics and certain strains can develop resistance, making it hard to treat in patients.

All these factors make this bacterium very important and dangerous, which with simple prevention techniques such as washing hands, infections can be deterred. This nosocomial infection needs to have a higher profile, due to the target population, high frequency and the diseases it causes, so further cases can be avoided.