Characterization of Escherichia coli bloodstream isolates associated with mortality.

Extra-intestinal pathogenic Escherichia coli (ExPEC) are the predominant cause of Gramnegative bloodstream infections. In this study, 20 E. coli isolates that were the causative agents of bacteraemia and subsequent mortality were characterized. Whole-genome sequencing was used to define the predominant sequence types (ST) among the isolates and to identify virulence factors associated with pathogenicity of ExPEC. The ability of the isolates to resist killing by both serum and polymorphonuclear leukocytes (PMNLs) was also assessed. In line with global trends, ST131 occurred most frequently among the bloodstream isolates and all isolates of this sequence type were multidrug resistant. Other common STs included ST73 and ST69. All isolates encoded multiple virulence factors across a range of categories, including factors involved in adhesion, immune evasion, iron acquisition and synthesis of toxins. None of these factors could be associated with serum and neutrophil resistance. The majority of isolates were resistant to the bactericidal action of serum and PMNLs, and most of those that were sensitive were isolated from patients with compromised immunity.