In the 1950s, the U.S. Army conducted experiments using Serratia marcescens as part of biological warfare testing. For example, during Operation Sea-Spray in 1950, Serratia marcescens was released over San Francisco to study its dispersal in the atmosphere. This led to concerns about the potential health effects of such experiments. 

Serratia marcescens is not a parasite. It is a bacterium, and the two are distinct categories in microbiology.