Molecular and Phenotypic Characterization of Diarrheagenic Escherichia coli Strains Isolated from Bacteremic Children

Escherichia coli is an important cause of Gram-negative bacteremia. The aim of this study was to characterize at the molecular and phenotypic levels E. coli strains belonging to different diarrheagenic pathotypes [diarrheagenic E. coli (DEC)] isolated from bacteremia in children younger than 5 years of age. Seventy bacteremia E. coli strains were collected in a prospective study in 12 hospitals in Lima, Peru. The presence of virulence genes associated with DEC [enterotoxigenic (lt and st), enteropathogenic (eaeA), shiga toxin-producing (stx1and stx2), enteroinvasive (ipaH), enteroaggregative (aggR), and diffusely adherent (daaD)] was determined by multiplex real-time polymerase chain reaction (PCR). Those positive E. coli strains were further analyzed for 18 additional virulence factors encoding genes and others phenotypic features. Virulence genes associated with DEC were identified in seven bacteremic children (10%), including: one aggR-positive [enteroaggregative E. coli (EAEC)], one eaeA-positive [enteropathogenic E. coli (EPEC)], one st-positive [enterotoxigenic E. coli (ETEC)], one daaD-positive [diffusely adherent E. coli (DAEC)], and three strain positive for aggR and daaD (EAEC/DAEC) at the same time. All strains, except EPEC, had the Ag43 adhesin, and all, except ETEC had the siderophore gene fyuA. The phylogenetic profile of these strains was variable, two (B2), two (D), two (A), and one (B1) strain. These isolates were susceptible to all tested antibacterial agents except to ampicillin and gentamicin. The three EAEC/DAEC strains showed biofilm formation and aggregative adhesion and had the same repetitive extragenic palindromic-PCR patterns. These findings suggest that some DEC strains, especially agg-R and daa-D positive, might cause bacteremia in children.