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

Recently, a new species, <i>Serratia sarumanii</i>, was described, belonging to a group of strains previously identified as <i>Serratia marcescens</i> in routine clinical analyses. It was shown that the identification of <i>S. marcescens</i> isolates by biochemical testing, mass spectrometry, or 16S rRNA gene sequencing was insufficient to resolve the '<i>S. marcescens</i> complex', while sampling point analysis revealed that many genomes assigned to the <i>S. sarumanii</i> cluster were associated with a clinical context. Thus, here the clinical relevance and local as well as global distribution of <i>S. sarumanii</i> is analyzed. In total, 21 strains from three hospitals in Eastern Westphalia-Lippe (OWL), previously identified as <i>S. marcescens</i> 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 <i>S. marcescens</i>, whereas 10 of the 21 isolates were identified as <i>S. sarumanii</i>, indicating that <i>S. sarumanii</i> is the dominant representative of the "<i>Serratia marcescens</i>" complex in hospitals in OWL. To analyze the global species distribution, all <i>Serratia</i> genomes available in GenBank were reclassified. About one-third of these genomes were identified as <i>S. sarumanii</i>, indicating <i>S. sarumanii</i> as the most dominant <i>Serratia</i> species in clinical settings around the world.