"S. liquefaciens" is the second best characterized species after "S. marcescens. S. liquefaciens" was first classified as Aerobacter liquefaciens in the Enterobacter genus by Grimes and Hennerty. The first documentation of "S. liquefaciens" was in 1971. Over 20 isolates of "S. liquefaciens" were recovered from different specimens such as urinary and respiratory. Out of the isolates, 6 of them were believed to cause infection in humans. From the 70s to 80s, this species was the cause of several hospital outbreaks. However, the most well-known outbreak occurred in Colorado at a hemodialysis center. During this outbreak, there were 10 "S. liquefaciens" bloodstream infections.