The Fires of Isengard Have Spread: Serratia sarumanii Is the Dominant Species in Clinical Isolates of the "Serratia marcescens Complex"

Recently, the new species Serratia sarumanii was described, belonging to a group of strains previously identified as Serratia marcescens in routine clinical analyses. It was shown that the identification of S. marcescens isolates by biochemical testing, mass spectrometry or 16S rRNA gene sequencing was insufficient to resolve the ‘S. marcescens complex’, while sampling point analysis revealed that many genomes assigned to the S. sarumanii cluster were associated with a clinical context. Thus, here the clinical relevance and local as well as global distribution of S. sarumanii is analyzed. In total, 21 strains from three hospitals in Eastern Westphalia-Lippe (OWL), previously identified as S. marcescens and potential causative agents from severe bacterial infections, were analyzed by genome sequencing and species identification. It could be shown that only one isolate was confirmed as S. marcescens, whereas 10 of the 21 isolates were identified as S. sarumanii, indicating that S. sarumanii is the dominant representative of the “Serratia marcescens” complex in hospitals in OWL. To analyze the global species distribution, all Serratia genomes available in GenBank were re-classified. About one third of these genomes were identified as S. sarumanii, indicating S. sarumanii as the most dominant Serratia species in clinical settings around the world.