Enteroaggregative Escherichia coli (EAEC) is a common diarrhoeagenic human pathogen, isolated
from patients in both developing and industrialized countries, that is becoming increasingly
resistant to many frontline antibiotics. In this study, we screened 50 E. coli strains from children
presenting with diarrhea at the outpatients clinic of Assiut University Children’s Hospital, Egypt.
We show that all of these isolates were resistant to multiple classes of antibiotics and identified
two as being typical EAEC strains. Using whole genome sequencing, we determined that both
isolates carried, amongst others, blaCTX-M and blaTEM antibiotic resistance genes, as well as many
classical EAEC virulence determinants, including the transcriptional regulator, AggR. We demonstrate
that the expression of these virulence determinants is dependent on AggR, including aar,
which encodes for a repressor of AggR, Aar. Since biofilm formation is the hallmark of EAEC
infection, we examined the effect of Aar overexpression on both biofilm formation and AggRdependent
gene expression. We show that whilst Aar has a minimal effect on AggR-dependent
transcription it is able to completely disrupt biofilm formation, suggesting that Aar affects these
two processes differently. Taken together, our results suggest a model for the induction of
virulence gene expression in EAEC that may explain the ubiquity of EAEC in both sick and healthy
individuals.
ARTICLE HISTORY
Received 28 August 2020
Revised 24 November 2020
Accepted 1 December 2020
KEYWORDS
EAEC; antibiotic resistance;
virulence; bacterial gene
regulation; genome
sequencing
Introduction
Diarrhoeagenic Escherichia coli strains are important
human pathogens, which cause considerable morbidity
and mortality around the globe, particularly amongst
infants and children in developing countries. These
pathogens are classified into different pathotypes,
which include enteroaggregative E. coli (EAEC), enterohaemorrhagic
E. coli (EHEC), enteroinvasive E. coli
(EIEC), enteropathogenic E. coli (EPEC), enterotoxigenic
E. coli (ETEC) and diffuse adhering E. coli
(DAEC), based on their disease characteristics and specific
adherence patterns [1]. Enteroaggregative
Escherichia coli (EAEC) is a commonly isolated
human pathogen that is responsible for causing mucoid
diarrhea in patients from both industrialized and developing
countries [2–5]. EAEC has been shown to elicit
travelers’ diarrhea, pediatric diarrhea, impairment of
pediatric growth and cognition, and even extraintestinal
infections, such as urinary tract infections
and septicemia [4,6–11]. In addition, EAEC strains
have b