Hopkins ABX Guide

Serratia Bacteria

What are Serratia Bacteria?

Serratia is a genus of bacteria from the Enterobacteriaceae family. The genus consists of more than 10 species which are normally non-pathogenic. In other words, they usually aren’t harmful to human health and they usually don’t cause any health complications if exposed to them. However, all species in the genus are classified as opportunistic pathogens which means that they aren’t exactly harmless and that it is possible to develop an infection. Most Serratia infections are caused by the species Serratia marcescens but infections with other species from the genus have been reported as well, with the majority occurring in the hospital environment.

Discovery and History Until the 1950s

The first bacterium in the genus was discovered by the Italian pharmacist Bartolomeo Bizio in 1819. He correctly identified Serratia marcescens to be responsible for reddish discolouration of boiled cornmeal known as polenta. In the early 20th century, the bacterium came to be used as a biological marker. Until the mid-20th century, it was thought to be completely harmless and non-pathogenic.

Use in Military Experiments

In the 1950s, the U.S. Army used Serratia marcescens for a very controversial experiment. Due to the red pigment produced on soil and water, and due to the fact that it was considered non-pathogenic, the U.S. Army decided to spray San Francisco area with a huge cloud of Serratia marcescens to evaluate the risk of biological warfare. And by spraying the bacteria during weather conditions that were favourable for dispersion, hundreds of thousands of people were exposed to this bacterium.

Shortly after the experiment, a dramatic increase of urinary tract infections and pneumonia was reported in the areas that were sprayed but the cause of these infections remained unexplained until the mid-1970s when the incident was finally unveiled. Serratia marcescens was identified as an opportunistic pathogen only in the 1960s, that is one decade after the controversial military experiment.

Symptoms of Infection, Risk Factors and Treatment

As mentioned earlier, the majority of Serratia infections are caused by the marcescens species, with the overwhelming majority being hospital-acquired. People at increased risk of infection are thus hospitalised individuals. Symptoms of the infection depend on the severity and location. It most often affects urinary and respiratory tracts, causing urinary tract infection and pneumonia, respectively. But it can also cause wound infection.

Serratia bacteria are naturally resistant to many commonly used antibiotics but there are several groups that are very effective for infections caused by Serratia marcescens as well as other species from the genus.