Prevalence of enteroaggregative Escherichia coli and its virulence-related genes in a case–control study among children from north-eastern Brazil

Abstract

Enteroaggregative Escherichia coli (EAEC) is an important agent that causes endemic and epidemic diarrhoeal diseases worldwide. Several EAEC virulence-related genes (VRGs) have been described but their role in the clinical outcome of infection is not completely defined. This study investigated the prevalence of EAEC and potential associations of its VRGs with risk of or protection from diarrhoeal diseases in children from urban communities in north-eastern Brazil. The case-control study included 166 children, who had their stools evaluated for the EAEC diagnostic genes (aaiC and aatA) using PCR. Positive samples were further analysed by multiplex PCR and identified 18 VRGs. EAEC was found in the same proportion in both groups (41 %). The plasmid-borne gene encoding a hexosyltransferase homologue (capU) was the most frequently detected (89.6 %), followed by dispersin protein (aap, 58.2 %) and EAEC HilA homologue (eilA, 57.8 %). The AAF/III fimbrial subunit (agg3A) gene was observed at lower frequency (1.5 %). Plasmid-encoded toxin (pet) or AAF/II fimbrial subunit (aafA) was associated significantly with disease. AAF/IV fimbrial subunit (agg4A) or hypothetical plasmid-encoded haemolysin (orf61) was detected significantly more in controls than in children with diarrhoea. In addition, one set of genes in combination, aaiC and agg3/4C but lacking agg4A and orf61, was associated with diarrhoea cases; and another one, orf61 in the absence of pet and aafA, was correlated with control children. These data confirm a high prevalence, endemicity and heterogeneity of EAEC strains in the developing urban areas of north-eastern Brazil. Statistical correlation between cases and controls was seen with either isolated or combined sets of genes, suggesting that the pathophysiology of EAEC infection involves a complex and dynamic modulation of several VRGs.

Phenotypic and Molecular Characterization of Enteroaggregative <i>Escherichia coli</i> Isolated in Kawasaki, Japan

“…Therefore, we infer the importance of evaluating the grade according to the thickness of the scum layer formed. Results show that 65 (26 strains) harbored one of the AAF genes, which indicates that the frequency of EAEC strains harboring AAF genes in our study is higher than that found in other countries (22,25). The classification of aggR-positive E. coli as EAEC in this study might have contributed to this high figure.…”

Novel Aggregative Adherence Fimbria Variant of Enteroaggregative Escherichia coli

“…Nevertheless, despite EAEC implications in several clinical scenarios, the molecular epidemiology of this pathogen remains unclear. This is mostly due to the heterogeneity of strains, and even though several virulence genes have been identified in EAEC, none have shown to be present in all strains (11)(12)(13)(14), making the recognition of truly virulent strains difficult.Several reports suggest that the key step in EAEC pathogenesis is the ability of the pathogen to adhere to and colonize the intestinal tract, which in EAEC prototype strains is facilitated by aggregative adherence fimbriae (AAF), followed by heavy biofilm formation (15-18). Four variants of the AAF major structural subunit have been described so far: AggA (AAF/I), AafA (AAF/II), Agg3A (AAF/III), and Agg4A (AAF/IV), all regulated by the transcriptional activator AggR, situated on the EAEC virulence plasmid pAA (19)(20)(21)(22)(23).…”

“…Nevertheless, despite EAEC implications in several clinical scenarios, the molecular epidemiology of this pathogen remains unclear. This is mostly due to the heterogeneity of strains, and even though several virulence genes have been identified in EAEC, none have shown to be present in all strains (11)(12)(13)(14), making the recognition of truly virulent strains difficult.…”

“…AAFs and Dr adhesins display a high level of conservation of the usher and chaperone genes and a sequence divergence of the fimbrial subunit genes (24). Previous studies have shown that approximately one-half of clinical EAEC isolates do not express any of the four known AAF variants, despite the presence of the pAA plasmid and/or other EAEC-specific genes (11,12). In this study, we investigated 118 Danish EAEC strains for the presence of AAF genes.…”

Research Article Novel multiplex PCR for detection of diarrheagenic Escherichia coli strains isolated from stool and water samples.

“…This study opted to study a chromosomal gene (aaiC). As shown by Lima et al (2013) the aaiC gene is a good candidate for molecular diagnosis because it has a chromosomal origin and is more prevalent that plasmid genes in EAEC. Our findings for aaiC and aggR revealed that the difference between the molecular diagnosis of chromosomal and plasmid genes was 59 strains positive for aaiC and only 48 for aggR (Table 2).…”