Serological typing and different types of polymerase chain reaction can be used to identify the "Serratia". Biotyping, bacteriocin typing, phage typing, plasmid analysis, and ribotyping can also be used. Most strains of "S. marcescens" appear red on trypticase soy agar slants when grown at around 25 °C. "S. marcescens" and "S. liquefaciens" can be easily confused in the lab when using the analytical profile index system. They can both oxidise arabinose, but only "S. liquefaciens" can ferment arabinose in peptone water. The virulence of "Serratia" strains can also be identifiable by type 4 fimbriae, small hair-like projections.