Characterization of Escherichia coli strains belonging to the emerging ExPEC-STEC hybrid pathotype through whole genome sequencing. hybrid ExPEC-STEC

Shiga toxin-producing E. coli serogroup O80, involved in Haemolytic Uremic Syndrome (HUS) associated with bacteremia, has emerged in Europe in the last decade, being one of the predominant serogroup in paediatric HUS cases reported in France since 2015. STEC O80 have been described as belonging to a hybrid pathotype, possessing intestinal virulence features, including LEE locus, the stx2 genes and a plasmid resembling the pO157, as well as the mosaic plasmid pR444_A, which combines virulence features characteristic of Extraintestinal Pathogenic E. coli (ExPEC) with multiple determinants of antimicrobials resistance.Here we report the characterization through whole genome sequencing of ExPEC-STEC strains isolated in Italy and the Netherlands in the period 2000-2019 and we demonstrate for the first time the detection of ExPEC-STEC of multiple serotypes. We identified 53 hybrid ExPEC-STEC strains belonging to 10 different serotypes, using the hlyF gene as hallmark of the presence of the pR444_A. The genome characterization revealed the presence of two different population of these hybrid strains of different origin: one included isolates belonging to ST301, possessing the flagellar H antigen H2 and harbouring, the stx2 gene, the intimin variant eae-ξ, the ehxA gene, and the whole pR444_A; the other included strains bolenging to other six STs and lacking the pO157-like plasmid, the LEE locus and the AMR-encoding region. Four of these isolates carried also the hlyA gene typical of UPEC strains. The phylogenetic comparison performed through cgMLST analysis gouped all the ST301 strains together and apart from the others, confirming the hypothesis according to which the ExPEC-STEC strins belong to at least two different lineages.Our results confirm the circulation of ExPEC-STEC strains in Europe and confirm their strong pathogenic potential. ExPEC-STEC cross-pathotype represent a serious threat for public health, therefore it should be carefull monitored.