Characterization of extended-spectrum-beta-lactamase-producing Escherichia coli strains involved in maternal-fetal colonization: prevalence of E. coli ST131

Abstract

Maternal-fetal Escherichia coli infections, such as neonatal bacteremia and meningitis, are important causes of morbidity and mortality. From 2006 to 2010, we studied newborns and their mothers who were colonized with E. coli in a French hospital in order to document (i) the epidemiology and genetic characteristics of extended-spectrum-beta-lactamase (ESBL)-producing E. coli strains, (ii) the prevalence of associated virulence genes, (iii) the prevalence of clone sequence type 131 (ST131), and (iv) the genetic relationship among ESBL-producing strains. Among the 2,755 E. coli cultures recovered from vaginal or neonatal samples, 68 were ESBL producers (2.46%). We found a wide diversity of ESBL genes, with the majority being bla(CTX-M-14), bla(CTX-M-1), and bla(CTX-M-15), distributed among the 4 main phylogenetic groups. Genes encoding virulence factors were found in 90.7% of the isolates, with ≥ 2 virulence genes present in 76% of cases. The prevalence of ST131 among ESBL-producing E. coli isolates was 9.4% (6/64). Five of these 6 ST131 isolates possessed bla(CTX-M-15) enzymes (and also were resistant to quinolones), and one possessed bla(CTX-M-2) enzymes. Two possessed virulence genes, suggesting the presence of pathogenicity island IIJ96 (PAI IIJ96)-like domains. Pulsed-field gel electrophoresis (PFGE) revealed a high level of genomic diversity overall, except for 3 closely related isolates belonging to clonal group ST131. Repetitive PCR showed that the six ST131 isolates were closely related to ST131 control strains (>95% similarity). This study shows a high prevalence of ESBL-producing E. coli strains and clonal group ST131 in the French maternal-fetal population. These results suggest a widespread distribution of ESBL enzymes in the community and highlight the early transmission between mothers and neonates. These findings are worrisome, especially for this particularly vulnerable population.

Fig 1

Genetic relation among the 13 ESBL-producing E. coli strains in group B2, as determined by PFGE (the pulsotype could not be obtained for 1 strain). The framed isolates are those belonging to clonal group ST131. These 6 isolates yielded 4 different profiles.

Fig 2

Genetic relatedness of E. coli strains belonging to clonal group O25b:H4-ST131 and control strains, as determined with DiversiLab semiautomated rep-PCR typing. There are 4 control strains known to belong to ST131 and 4 unrelated control strains that do not belong to clonal group ST131. E. coli ST131 isolates 29369, 28678, 26601, 31342, 27144, and 30151 are those found in this maternal-fetal study. The six E. coli ST131 strains in our study were closely related to the ST131 control strains (>95% similarity) and exhibited a >15% difference with strains not belonging to this sequence type.