Enteroinvasive Escherichia coli O96:H19 is an Emergent Biofilm-Forming Pathogen

Acquisition of a large virulence plasmid (pINV) promoted temperature-dependent virulence and global dispersal of O96:H19 enteroinvasive Escherichia coli

Enteroinvasive Escherichia coli (EIEC) and Shigella are closely related agents of bacillary dysentery. It is widely viewed that EIEC and Shigella species evolved from E. coli via independent acquisitions of a large virulence plasmid (pINV) encoding a type 3 secretion system (T3SS). Sequence Type (ST)99 O96:H19 E. coli is a novel clone of EIEC responsible for recent outbreaks in Europe and South America. Here, we use 92 whole genome sequences to reconstruct a dated phylogeny of ST99 E. coli, revealing distinct phylogenomic clusters of pINV-positive and -negative isolates. To study the impact of pINV acquisition on the virulence of this clone, we developed an EIEC-zebrafish infection model showing that virulence of ST99 EIEC is thermoregulated. Strikingly, zebrafish infection using a T3SS-deficient ST99 EIEC strain and the oldest available pINV-negative isolate reveals a separate, temperature-independent mechanism of virulence, indicating that ST99 non-EIEC strains were virulent before pINV acquisition. Taken together, these results suggest that an already pathogenic E. coli acquired pINV and that virulence of ST99 isolates became thermoregulated once pINV was acquired. IMPORTANCE Enteroinvasive Escherichia coli (EIEC) and Shigella are etiological agents of bacillary dysentery. Sequence Type (ST)99 is a clone of EIEC hypothesized to cause human disease by the recent acquisition of pINV, a large plasmid encoding a type 3 secretion system (T3SS) that confers the ability to invade human cells. Using Bayesian analysis and zebrafish larvae infection, we show that the virulence of ST99 EIEC isolates is highly dependent on temperature, while T3SS-deficient isolates encode a separate temperature-independent mechanism of virulence. These results indicate that ST99 non-EIEC isolates may have been virulent before pINV acquisition and highlight an important role of pINV acquisition in the dispersal of ST99 EIEC in humans, allowing wider dissemination across Europe and South America.

Infection with a human-derived enteroinvasive Escherichia coli strain altered intestinal barrier function in guinea pigs

BACKGROUND/AIMS

The aim was to characterize a bacterium causing intestinal mucosal barrier damage and to identify the possible invasion mechanism.

MATERIALS AND METHODS

The intestinal permeability and tight junction protein levels were detected in guinea pigs infected with Escherichia coli D-09 via immunofluorescence analysis and western blotting. In order to explain this invasion mechanism at the gene level, whole genome sequencing analysis was performed on this bacterium.

RESULTS

The results showed an increased intestinal permeability and upregulated expression of the leaky protein claudin-2 in both the colon and liver of the infected animals. In addition, the draft genome of E. coli D-09 comprised 42 scaffolds (size, > 645 bp) with a total size of 4,679,567 bp. A total of 4379 protein coding genes were identified, which contained 45 antibiotic resistance and 86 virulence-related genes and covered 88.0% of the whole genome.

CONCLUSIONS

This study verified that the human-derived enteroinvasive E. coli strain could destroy intestinal barrier function in guinea pigs. Additionally, our data first characterized the genome features of E. coli O124:K72 D-09, which may provide new insights into the possible invasion mechanism.