Comparative genetic characterization of Enteroaggregative Escherichia coli strains recovered from clinical and non-clinical settings

Abstract

The origin of pathogenic Enteroaggregative Escherichia coli (EAEC), a major causative agent of childhood diarrhea worldwide, remains ill-defined. The objective of this study was to determine the relative prevalence of EAEC in clinical and non-clinical sources and compare their genetic characteristics in order to identify strains that rarely and commonly cause human diarrhea. The virulence gene astA was commonly detectable in both clinical and non-clinical EAEC, while clinical isolates, but not the non-clinical strains, were consistently found to harbor other virulence factors such as aap (32%), aatA (18%) and aggR (11%). MLST analysis revealed the extremely high diversity of EAEC ST types, which can be grouped into three categories including: (i) non-clinical EAEC that rarely cause human infections; (ii) virulent strains recoverable in diarrhea patients that are also commonly found in the non-clinical sources; (iii) organisms causing human infections but rarely recoverable in the non-clinical setting. In addition, the high resistance in these EAEC isolates in particular resistance to fluoroquinolones and cephalosporins raised a huge concern for clinical EAEC infection control. The data from this study suggests that EAEC strains were diversely distributed in non-clinical and clinical setting and some of the clinical isolates may originate from the non-clinical setting.

Figure 1. Distribution of sampling locations and sites where EAEC were recovered in Hangzhou, China.

The figure was generated by obtaining the map of Hanzhou city from Zhejiang Administration of Surveying Mapping and Geoinformation (ZheS(2010)280) with the agency’s permission and further refined by Adobe Photoshop CS2 software.

Figure 2. Minimal spanning tree based on multilocus sequence typing of EAEC isolates.

Colored circles represent different sequence types. Black connecting lines indicate single-locus variants; gray connecting lines indicate double-locus variants; dashed connecting lines indicate strains with ≥3 differing loci; and shadowing indicates that >2 sequence types belong to one clonal complex.