Serratia marcescens

Classification

Higher order Taxa

Bacteria(Domain); Proteobacteria(Phylum); Gamma Proteobacteria(Class); Enterobacteriales(Order); Enterobacteriaceae(Family); Serratia(Genus).

Species

Serratia marcescens

Description and Significance

Serratia marcescens was discovered in 1819 by Bartolomeo Bizio in Padua, Italy. Bizio attributed the red or bloody discoloration in cornmeal and breads. Bizio chose the name Serratia to honor his friend named Serratia and secondly marcescens, which is Latin for decay [3]. Serratia marcescens was first thought to be harmless (non-pathogenic). Due to its ability to produce red pigmentation, it was used in 1906 as a marker in order to trace bacterial activity or transmission [4]. It was not until later in the 1950’s, when US government experimented with the Serratia marcescens, that the harmful effects that the bacteria causes. A study using Serratia marcescens was carried out to determine the possibility of biological weapons being transmitted by wind current. It was soon after that there was an increase in the number of pneumonia and urinary tract infections [1]. Although the Serratia marcescens bacterium was classified as a human pathogen in the 1960s, scientist still used it as a bacterial tracer well into the 1970s [6].

Even though Serratia marcescens can be found in soil, water and some foods, it is an opportunistic pathogen and can therefore more often than not be seen in people with a compromised immune system. They are mobile bacteria. Optimally, Serratia marcescens grow at 37°C (a human body’s temperature), but it can grow in temperatures that range from 5–40°C. They grow in pH levels that range from 5 to 9 [9]. Serratia marcescens is well known for the red pigmentation it produces called prodigiosin. Prodigiosin has a skeleton that is made up of three pyrrole rings [10] and is not produced at 37°C, but at a lower temperature such as at 30°C [14]. In 1263 a priest with doubts of Christ’s presence in the consecrated Host presided over a mass in the Basilica of Bolsena. After speaking the words of consecration, blood began to drip from the consecrated Host onto his hands and the altar [1]. This event is now known as the Miracle of Bolsena and it was depicted by Raphael on the walls of the Vatican [13]. The red pigmented Serratia marcescens is not present in all strains but in those that it is present, it can resemble blood. Some scientists have tried to explain the miracle of “blood” in the consecrated Host by referring to the prodigiosin in Serratia marcescens [6].