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Fragments from Floyd

Serratia marcescens: Pathogen with a Past

S. marcescens on an agar plate
Image via Wikipedia

You might have heard about the IV contamination that has killed and sickened a number of people in Alabama. The organism is Serraatia marcescens. I seem to remember this creature from microbiology days. In my foggy recollection, I recalled that it was a soil organism, a bacterium of decay, and colorful–yellow or red on a petrie plate.

So I checked out my vague memory traces for S. marcescens; it has had an interesting history. Given my time crunch, I’ll just let the venerable Wikipedia do the talking: (emphasis, mine)

Until the 1950s, S. marcescens was erroneously believed to be a non-pathogenic “saprophyte”,[3] and its reddish coloration was used in school experiments to track infections. It has also been used as a simulant in biological warfare tests by the United States Military.[9][10]

On September 26 and 27, 1950, the United States 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 eleven 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.[11],[12]

Since 1950, S. marcescens has steadily increased as a cause of human infection, with many strains resistant to multiple antibiotics.[1] 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,[13] 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.[14]

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