Abstract
Virulence genes from different E. coli pathotypes are blended in hybrid strains. E. coli strains with hybrid enteroaggregative/uropathogenic (EAEC/UPEC) genotypes have sporadically emerged causing outbreaks of extraintestinal infections, however their association with routine infections is yet underappreciated. We assessed 258 isolates of E. coli recovered from 86 consecutive cases of extraintestinal infections seeking EAEC and hybrid genotype (EAEC/UPEC) strains. Extensive virulence genotyping was carried out to detect 21 virulence genes, including molecular predictors of EAEC and UPEC strains. Phylogenetic groups and sequence types (STs) were identified, as well as it was performed phylogenetic analyses in order to evaluate whether hybrid EAEC/UPEC strains belonged to intestinal or extraintestinal lineages of E. coli. Adhesion assays were performed to evaluate the biofilm formation by hybrid strains in human urine and cell culture medium (DMEM). Molecular predictors of UPEC were detected in more than 70% of the strains (chuA in 85% and fyuA in 78%). Otherwise, molecular predictors of EAEC (aatA and aggR) were detected in only 3.4% (9/258) of the strains and always along with the UPEC predictor fyuA. Additionally, the pyelonephritis-associated pilus (pap) gene was also detected in all of the hybrid EAEC/UPEC strains. EAEC/UPEC strains were recovered from two cases of community-onset urinary tract infections (UTI) and from a case of bacteremia. Analyses revealed that hybrid EAEC/UPEC strains were phylogenetically positioned in two different clades. Two representative strains, each recovered from UTI and bacteremia, were positioned into a characteristic UPEC clade marked by strains belonging to phylogenetic group D and ST3 (Warwick ST 69). Another hybrid EAEC/UPEC strain was classified as phylogroup A-ST478 and positioned in a commensal clade. Hybrid EAEC/UPEC strains formed biofilms at modest, but perceptible levels either in DMEM or in urine samples. We showed that different lineages of E. coli, at least phylogenetic group A and D, can acquire and gather EAEC and UPEC virulence genes promoting the emergence of hybrid EAEC/UPEC strains.
Highlights
Escherichia coli colonizes the human intestine few hours after birth establishing a mutually beneficial relationship with its hosts
uropathogenic E. coli (UPEC) virulence gene (VG) displayed an uneven distribution among phylogroups
enteroaggregative E. coli (EAEC) is a heterogeneous category that has been recognized for gathering versatile pathogens since the late 1990’s, when their epidemiological association with diarrhea involving children, adults, HIV-infected patients and travelers became more and more evident (Kaper et al, 2004)
Summary
Escherichia coli colonizes the human intestine few hours after birth establishing a mutually beneficial relationship with its hosts. While they are restricted to the outer layer of intestinal mucus, these commensal E. coli strains rarely cause infections. Pathogenic and commensal strains of E. coli are differently sorted into four major phylogenetic groups (phylogroups) named as A, B1, B2, and D (Doumith et al, 2012). Each E. coli phylogroup may enclose heterogeneous groups of strains and different clonal populations, fact which imposes a more complex scenario in an attempt to establish epidemiological links between E. coli phylogroups and human infections (Dias et al, 2009). The development of multilocus sequence typing (MLST) methods and the subsequent definition of sequence types (STs) pave the way to the recognition of highly virulent ExPEC clones with worldwide dispersion, such as the clones B2-ST131 and D-ST69 (Blanco et al, 2011; Nicolas-Chanoine et al, 2014; Petty et al, 2014)
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