The Miracle Microbe: Serratia marcescens

NAME: Serratia marcescens

IMAGE SIZE: 16 microns

IMAGE CREDITS: Shirley Owens and Catherine McGowan, Microbe Zoo Project, Comm Tech Lab, Michigan State University.

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The Miracle of Bolsena is depicted on the walls of the Vatican in this painting by Raphael. The German priest Peter of Prague is shown breaking bread for communion at the Church of Saint Christina in Bolsena, Italy.

Imagine Peter's surprise when he broke the communion wafer and saw it had blood on it! The bread had truly become Jesus' flesh!

Or had it?

The year was 1263, four hundred years before Antonie van Leeuwenhoek would first see bacteria under a microscope. In1264 to honor of the miracle of Bolsena, Pope Urban instituted the feast of Corpus Christi (Body of Christ). Neither the Pope nor Peter the Priest could ever have known that a red bacterium, Serratia marscesens, was the probable cause of this blood-like substance on the communion bread.

Most microbiologists are all too familiar with Serratia marscescens, one of the most frequent contaminants of Petri plates in the lab. This same organism also grows on bread and communion wafers which have been stored in a damp place.

This common microbe is found in soil, water, on plants and in animals.

Because this microbe is so common, because of its bright red color and because it used to be considered benign, scientists and teachers frequently used it in experiments to track microbes and to demonstrate the importance of hand washing. For example, it was used to in handshaking experiments in which one person dipped a hand in a broth of S. marcescens and then shook hands with another person who in turn shook the hand of another and so on down the line.

More recently, S. marcescens has been found to be pathogenic to some people, and it is no longer recommended for use in schools and is not as widely used to track bacterial movement in the environment.

S. marcescens has been used to determine the survival and fate of bacteria in saline breast implants. Serratia appears to thrive in saline breast implants, living on the glucose that diffuses across the implant's outer shell.

So maybe S. marcescens wasn't the miracle that the Pope expected, but this tiny organism does remind us of the miraculous invisible life that is all around.


For more stories about S. marsescens and other interesting microbes, read Power Unseen: How Microbes Rule the World by Bernard Dixon. Oxford Univ. Press; ISBN: 071674550X.


bacterium - (plural = bacteria) - a simple, small microbe lacking a nucleus. Bacteria are also called prokaryotes or monerans. Most bacteria are unicellular, containing only a single cell. Sometimes bacteria appear multicellular, living together in groups of cells. Bacteria comprise two of the three domains of life, the Eubacteria and the Archaea.

contaminant - an organism growing where it is not wanted.

pathogenic - disease causing. A microbe that causes disease is said to be pathogenic.

communion - Christian ceremony remembering the Last Supper of Christ. Some believe in transsubstantiation, in which the bread and wine of communion are turned into the presence of Christ.

Petri plates - dishes filled with jello-like nutrients used to grow microbes.

Pope Urban - instituted the feast of Corpus Christi (Body of Christ) in August 1264 after learning about the Miracle of Bolsena.

Rafael - Raffaello Sanzio (1483~1520),- great and influential artist of the Italian Renaissance. Raphael was born in Urbino, Italy. In 1504 Raphael moved to Florence where he learned from Leonardo and Michelangelo.




 © 1999 Comm Tech Lab, Michigan State Univeristy. This work was created with support from the National Science Foundation and the Center for Microbial Ecology at Michigan State University. Current maintenance is supported by the International Society for Microbial Ecology and the Comm Tech Lab.