Characterization and comparative analysis of the Escherichia marmotae M-12 isolate from bank vole (Myodes glareolus)

Abstract

The Escherichia marmotae is a bacterium of the Enterobacterales order, which was first isolated from the Himalayan marmot (Marmota himalayana). Recently E. marmotae has been shown to cause severe infections in humans. Wild animals were suggested to be a natural reservoir of this bacterium. The present study describes the first case of E. marmotae isolation from an apparently healthy wild bank vole (Myodes glareolus). Phenotype, as well as genotype-based techniques, were applied to characterize E. marmotae M-12 isolate. E. marmotae M-12 had the capsule-positive phenotype, high adhesion to human erythrocytes and HEp-2 cells as well as a low invasion into HEp-2 cells. E. marmotae M-12 was avirulent in mice. The phylogenomic analyses of E. marmotae showed dispersed phylogenetic structure among isolates of different origins. Virulome analysis of M-12 isolate revealed the presence of the following factors: siderophores, heme uptake systems, capsule synthesis, curli and type I fimbriae, flagella proteins, OmpA porin, etc. Comparative virulome analysis among available E. marmotae genomes revealed the presence of capsule K1 genes mostly in pathogenic isolates and OmpA porin presence among all strains. We assume that the K1 capsule and OmpA porin play a key role in the virulence of E. marmotae. Pathogenesis of the latter might be similar to extraintestinal pathogenic E. coli.

Figure 1

Light microscopy of capsules in the dark background (× 1800): (A) E. marmotae M-12 stained with gentian violet; (B) strain K. pneumoniae ML-9 stained with fuchsine.

Figure 2

Adhesion of E. marmotae M-12 bacterial cells to human erythrocytes (× 1800). Stained with Giemsa stain solution.

Figure 3

Adhesion and invasion activity of HEp-2 cells following infection by E. marmotae M-12, S. enterica subsp. enterica NCTC 5765, and E. coli XL-1 Blue. Statistical processing of data was performed via Newman–Keuls test. Adhesion activity between all strains had statistically significant differences (p ≤ 0.05). Invasion activity of E. coli XL-1 Blue and E. marmotae M-12 in comparison with the control S. enterica NCTC 5765 had statistically significant differences (p ≤ 0.01), while E. coli XL-1 Blue and E. marmotae M-12 did not have statistically significant differences. Results represented as means ± SD from at least three independent experiments in duplicate.

Figure 4

Phylogenetic tree of E. marmotae reconstructed with REALPHY 1.13.