Aerobic gram negative rod. S. liquifaciens, S. marcescens, S. odorifera, S. rubidaea.
Often invades by way of the respiratory tract.
Hospital acquired infections of all kinds.
It makes a red pigment that allowed the military to use it in the 50's to see how bacteria move in urban environments. For example, the US government sprayed aerosolized Serratia in San Francisco because they could track the organism by using drop plates and seeing how it spread in urban environments. People died. So much for it being a non-pathogen. It's red pigment has also been credited as the cause of bleeding paintings and food in the middle ages. See the NEJM review.