Emerging avian pathogenic Escherichia coli strains belonging to clonal groups O111:H4-D-ST2085 and O111:H4-D-ST117 with high virulence-gene content and zoonotic potential

The present study characterizes, for the first time, two emerging avian pathogenic Escherichia coli (APEC) clonal groups of serogroup O111: O111:H4-D-ST117 and O111:H4-D-ST2085. The clonal group O111:H4-D-ST117 was already present in APEC strains isolated between 1991 and 2000, and was still present in strains isolated between 2004 and 2009, showing long time evolution according to the virulence-gene differences and macrorestriction profiles. Among ST117 strains, two virulence profiles could be distinguished: papG II-positive tsh-negative strains which satisfied criteria for extraintestinal pathogenic E. coli (ExPEC), and papG II-negative tsh-positive strains without ExPEC status. Interestingly, we have detected a human septicemic O111:H4-D-ST117 ExPEC strain isolated from a hemocultive in 2000 whose macrorestriction profile showed >85% similarity with four APEC strains of the study. The clonal group O111:H4-D-ST2085 was exclusively detected in 17 APEC strains isolated in 2008 and 2009, and showed short time evolution based on its homogeneity since all were nalidixic acid-resistant, all had ExPEC status, and most carried papG II and tsh genes. From the clinical point of view, O111:H4-D-ST2085 seems a successful clonal group that could be the result of the epidemiological evolution of O111:H4-D-ST117. Due to the increasing prevalence of both clonal groups among clinical APEC isolates, their high virulence-gene content, and zoonotic potential, we suggest them as possible candidates for the development of a future vaccine against avian colibacillosis.