Multilocus sequence typing identifies disease-causing Shewanella chilikensis strain 6I4

Abstract

The genus Shewanella is rapidly expanding, with new species being discovered frequently. Four species have been identified as pathogenic to humans, with Shewanella algae being most relevant. Evaluation of the clinical significance of species still suffers from the imprecision of species identification. In addition, the origin of S. algae strains causing disease is unclear. To shed light upon these questions we re-identified reportedly S. algae isolates on the species level based on partial sequences of the 16S rRNA and gyrB genes in combination with multilocus sequence analysis of six housekeeping loci. We used a collection of twenty-three S. algae isolates of clinical and environmental origin and the publicly available genome sequences of six additional S. algae strains. Our analysis showed the existence of a remarkable haplotypic diversity and a clonal population structure within the S. algae clade, and revealed that three of the analyzed strains should be assigned to a species different from S. algae. A clinical isolate was thus reclassified as S. chilikensis, thereby constituting the first known case of human infection by this species. Our study emphasizes the application of high resolution molecular markers for species identification. The taxonomic resolution of the S. algae clade is still unclear.

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