Analysis of the Virulence Profile and Phenotypic Features of Typical and Atypical Enteroaggregative Escherichia coli (EAEC) Isolated From Diarrheal Patients in Brazil

Abstract

Enteroaggregative Escherichia coli (EAEC) is an important agent of acute and persistent diarrhea in children and adults worldwide. Here we report a characterization of 220 EAEC isolates, 88.2% (194/220) of which were typical and 11.8% (26/220) were atypical, obtained from diarrheal patients during seven years (2010-2016) of epidemiological surveillance in Brazil. The majority of the isolates were assigned to phylogroups A (44.1%, 97/220) or B1 (21.4%, 47/220). The aggregative adherence (AA) pattern was detected in 92.7% (204/220) of the isolates, with six of them exhibiting AA concomitantly with a chain-like adherence pattern; and agg5A and agg4A were the most common adhesin-encoding genes, which were equally detected in 14.5% (32/220) of the isolates. Each of 12 virulence factor-encoding genes (agg4A, agg5A, pic, aap, aaiA, aaiC, aaiG, orf3, aar, air, capU, and shf) were statistically associated with typical EAEC (P < 0.05). The genes encoding the newly described aggregate-forming pili (AFP) searched (afpB, afpD, afpP, and afpA2), and/or its regulator (afpR), were exclusively detected in atypical EAEC (57.7%, 15/26), and showed a significant association with this subgroup of EAEC (P < 0.001). In conclusion, we presented an extensive characterization of the EAEC circulating in the Brazilian settings and identified the afp genes as putative markers for increasing the efficiency of atypical EAEC diagnosis.

Keywords: EAEC; antimicrobial resistance; diagnosis; diarrhea; virulence factors.

Figure 1

Representative images of the distinct patterns of adherence exhibited by the EAEC isolates studied in adherence assays performed with HeLa cells. The adherence patterns are illustrated as follow: (A) aggregative adherence pattern, (B) aggregative adherence pattern (solid arrow) occurring concomitantly with the chain-like adherence (dashed arrow), (C) chain-like adherence pattern, and (D) diffuse adherence pattern. All the adherence patterns illustrated in this picture were observed in adherence assays performed with 3 h of infection. Scale bar = 10 μm.

Figure 2

Aggregative adherence (AA) pattern exhibited by an atypical EAEC (aatA⁺/aggR⁻) isolate (IAL 6006) that harbored the afp operon. Note the bacterial stacked brick-like arrangement, characteristic of the AA pattern, on both epithelial cells and coverslip surfaces detected in adherence assay performed with 3 h of infection. Scale bar = 10 μm.