Enteroaggregative Escherichia coli Is a Cause of Acute Diarrheal Illness: A Meta-Analysis

Enteroaggregative Escherichia coli in mid-Norway: A prospective, case control study

BACKGROUND

The use of molecular methods has led to increased detection of Enteroaggregative Escherichia coli (EAEC) in faecal samples. Studies have yielded conflicting results regarding the clinical relevance of this finding. The objective of this study was to investigate the prevalence of EAEC in faecal samples from patients with diarrhoea and healthy controls and describe characteristics of EAEC positive persons.

METHODS

From March 1st, 2017 to February 28th, 2019, we investigated all consecutive faecal samples from patients with diarrhoea received at the laboratory and collected faecal samples from randomly invited healthy controls from mid-Norway. Real-time multiplex PCR was used for detection of bacterial, viral, and parasitic pathogens. We registered sex, age, urban versus non-urban residency, and travel history for all participants. Statistical analyses were performed with Pearson chi-squared test, Kruskal-Wallis test, and Mann-Whitney U test.

RESULTS

We identified EAEC in 440 of 9487 (4.6%) patients with diarrhoea and 8 of 375 (2.2%) healthy controls. The EAEC prevalence was 19.1% among those with diarrhoea and recent foreign travel and 2.2% in those without travel history independent of diarrhoea. Concomitant pathogens were detected in 64.3% of EAEC-positive patients with diarrhoea. The median age was 28.5 in those with EAEC-positive diarrhoea and 38 in those with EAEC-negative diarrhoea (p <0.01). In patients with diarrhoea, travel was reported in 72% of those with EAEC and concomitant pathogens, and 54% and 12% in those with only EAEC and no EAEC, respectively (p <0.01).

CONCLUSIONS

EAEC was a common detection, particularly in patients with diarrhoea and recent international travel, and was found together with other intestinal pathogens in the majority of cases. Our results suggest that domestically acquired EAEC is not associated with diarrhoea. Patients with EAEC-positive diarrhoea and concomitant pathogens were young and often reported recent travel history compared to other patients with diarrhoea.

Pathogenic E. coli in the Food Chain across the Arab Countries: A Descriptive Review

Foodborne bacterial infections caused by pathogens are a widespread problem in the Middle East, leading to significant economic losses and negative impacts on public health. This review aims to offer insights into the recent literature regarding the occurrence of harmful E. coli bacteria in the food supply of Arab countries. Additionally, it aims to summarize existing information on health issues and the state of resistance to antibiotics. The reviewed evidence highlights a lack of a comprehensive understanding of the extent to which harmful E. coli genes are present in the food supply of Arab countries. Efforts to identify the source of harmful E. coli in the Arab world through molecular characterization are limited. The Gulf Cooperation Council (GCC) countries have conducted few surveys specifically targeting harmful E. coli in the food supply. Despite having qualitative data that indicate the presence or absence of harmful E. coli, there is a noticeable absence of quantitative data regarding the actual numbers of harmful E. coli in chicken meat supplies across all Arab countries. While reports about harmful E. coli in animal-derived foods are common, especially in North African Arab countries, the literature emphasized in this review underscores the ongoing challenge that harmful E. coli pose to food safety and public health in Arab countries.

Evaluating outpatient diagnostic stewardship of comprehensive polymerase chain reaction Clostridioides difficile testing in a regional health system

Objective

We examined the use of comprehensive and targeted polymerase chain reaction (PCR) of Clostridioides difficile infection (CDI) among immunocompetent patients with and without CDI risk factors across different outpatient settings. A priori, we expected patients with higher CDI risk to be associated with targeted testing to reflect providers incorporating pretest risk factors in their choice of test assay.

Design

Retrospective analysis of adult patients from clinic, emergency room, and non-medically acute inpatient settings.

Setting

A tertiary academic medical center offering inpatient and outpatient medical, surgical, mental health, and rehabilitation services to Veterans across the Puget Sound region.

Patients

Immunocompetent adult patients with ≥1 stool PCR assay performed between January 2016 and December 2019.

Intervention

Patients were tested with either a specific tcdB PCR assay or a comprehensive gastrointestinal PCR panel that tests for 22 pathogens.

Results

A total of 2,717 tests (74% targeted, 26% comprehensive) were obtained from 2,156 patients, among which 13% detected C. difficile and 7% detected other organisms. The proportion of comprehensive PCR tests increased nearly four-fold from 2016 to 2019 in clinic and emergency room settings, independent of CDI risk factors. Only two CDI risk factors (prior history of CDI and antibiotic use within three months before testing) were associated with increased targeted testing.

Conclusion

The use of comprehensive GI PCR among immunocompetent adults with diarrhea is increasing in the outpatient setting. There may be an opportunity for diagnostic stewardship by nudging providers to consider all CDI risk factors at the time of test selection.

Are non-lactose-fermenting Escherichia coli important diarrhoeal pathogens in children and adults?

Introduction

Diarrhoeagenic Escherichia coli (DEC) remains one of the major causes of acute diarrhoea episodes in developing countries. The percentage of acute diarrhoea cases caused by DEC is 30-40 % in these countries. Approximately 10% of E. coli isolates obtained from stool specimens have been reported to be non-lactose-fermenting (NLF). The available literature is sparse regarding the pathogenicity of NLF E. coli causing infectious diarrhoea.

Aim

We aimed to elucidate the importance of NLF E. coli in causing diarrhoea in both adults and children by detecting various DEC pathotypes among NLF E. coli in stool samples taken from gastroenteritis cases.

Material and Methods

A total of 376 NLF E. coli isolates from 3110 stool samples from diarrhoea/gastroenteritis patients were included in the study. Up to three NLF colonies that were not confirmed as Vibrio cholerae , Aeromonas spp., Salmonella spp. or Shigella spp., but were identified as E. coli using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF), were carefully picked up from each MacConkey agar plate and then meticulously streaked onto freshly prepared, sterilized nutrient agar plates, and biochemical reactions were conducted. Multiplex PCR was conducted for the EAEC, EPEC, ETEC and EHEC pathotypes and PCR for the ipaH gene was conducted for EIEC. The disc diffusion method was used for antibiotic sensitivity testing.

Results

Using multiplex PCR and ipaH PCR, a total of 63 pathotypes of DEC were obtained, with EAEC being the most predominant (n=31) followed by EIEC (n=22), EPEC (n=8) and ETEC (n=2). To further differentiate EIEC from Shigella , additional biochemical tests were performed, including acetate utilization, mucate and salicin fermentation, and aesculin hydrolysis. Antimicrobial susceptibility testing (AST) showed that maximum resistance was seen against ciprofloxacin (82.5 %) followed by ampicillin (77.8 %) and cotrimoxazole (68.2 %), and minimum resistance was seen against ertapenem (4.8 %).

Conclusion

In our study two pathotypes (EAEC, EIEC) were predominant among NLF E. coli and these were not only important aetiological agents in children, but also in adults. Our study also sheds light on the epidemiology of EIEC, which is one of the most neglected DEC pathotypes, as hardly any microbiological laboratories process NLF E. coli for EIEC.

Real-time multiplex PCR assay reveals the increased prevalence of Campylobacter spp and diarrhoeagenic Escherichia coli in humans from Vellore, South India

Introduction. Bacterial dysentery is one of the greatest causes of morbidity and mortality worldwide. Campylobacter spp. and diarrhoeagenic Escherichia coli (DEC) are recognised as the most common causes of bacterial enteritis in developing countries including India.Hypothesis/Gap statement. Rapid and accurate identification of dysentery causing organisms using molecular methods is essential for better disease management, epidemiology and outbreak investigations.Aim. In view of the limited information available on the dysentery causing agents like Campylobacter spp., enterohemorrhagic E. coli (EHEC)/enteropathogenic E. coli (EPEC) and enteroinvasive E. coli (EIEC)/Shigella in India, this study was undertaken to investigate the presence of these pathogens in human and poultry stool samples by molecular methods.Methodology. In total, 400 human stool samples and 128 poultry samples were studied. Microaerophilic culture along with real-time multiplex PCR with the targets specific to the genus Campylobacter, Campylobacter jejuni, Campylobacter coli, EHEC, EPEC and EIEC/Shigella was performed. Further species confirmation was done using MALDI-TOF MS.Results. On microaerophilic culture, C. coli was isolated in one human sample and two C. jejuni and one C. fetus in poultry samples. On PCR analysis, among human stool samples, typical EPEC (42%) was predominantly seen followed by Campylobacter spp. (19%) and EIEC/Shigella (10%). In contrast, Campylobacter spp. (41%) was predominant in poultry samples, followed by typical EPEC (26%) and EIEC/Shigella (9%). Poly-infections with Campylobacter spp. and DEC were also observed among both sources.Conclusion. The present study documented the increased prevalence of Campylobacter spp. in humans compared with the results of previous studies from India. Typical EPEC was found to be predominant in children less than 5 years of age in this study. The high prevalence of coinfections in the current study indicates that a multiple aetiology of diarrhoea is common in our settings.

The aggregate-forming pili (AFP) mediates the aggregative adherence of a hybrid-pathogenic Escherichia coli (UPEC/EAEC) isolated from a urinary tract infection

Enteroaggregative Escherichia coli (EAEC) comprises an important diarrheagenic pathotype, while uropathogenic E. coli (UPEC) is the most important agent of urinary tract infection (UTI). Recently, EAEC virulence factors have been detected in E. coli strains causing UTI, showing the importance of these hybrid-pathogenic strains. Previously, we detected an E. coli strain isolated from UTI (UPEC-46) presenting characteristics of EAEC, e.g., the aggregative adherence (AA) pattern and EAEC-associated genes (aatA, aap, and pet). In this current study, we analyzed the whole genomic sequence of UPEC-46 and characterized some phenotypic traits. The AA phenotype was observed in cell lineages of urinary and intestinal origin. The production of curli, cellulose, bacteriocins, and Pet toxin was detected. Additionally, UPEC-46 was not capable of forming biofilm using different culture media and human urine. The genome sequence analysis showed that this strain belongs to serotype O166:H12, ST10, and phylogroup A, harbors the tet, aadA, and dfrA/sul resistance genes, and is phylogenetically more related to EAEC strains isolated from human feces. UPEC-46 harbors three plasmids. Plasmid p46-1 (~135 kb) carries some EAEC marker genes and those encoding the aggregate-forming pili (AFP) and its regulator (afpR). A mutation in afpA (encoding the AFP major pilin) led to the loss of pilin production and assembly, and notably, a strongly reduced adhesion to epithelial cells. In summary, the genetic background and phenotypic traits analyzed suggest that UPEC-46 is a hybrid strain (UPEC/EAEC) and highlights the importance of AFP adhesin in the adherence to colorectal and bladder cell lines.

Genetic diversity of enteroaggregative Escherichia coli

Studied 74 E. coli strains isolated from stool samples (60) and urine samples (14) of patients examined for clinical indications. Molecular methods included: PCR with electrophoretic detection of genes associated with diarrheal E. coli pathogroup EAgEC (aggR, aaf, aap, aatA, pet, ast, aai) and ExPEC pathogroup UPEC (pap, sfa, afa, kpsMT II, iutA, hlyA, cnf), MLST typing, whole genome sequencing. Strains isolated from stool samples were significantly more likely (88.3%, p > 0.05) to be typical EAgECaggR+ compared to atypical EAgECaggR-. Strains isolated from urine samples, significant differences between typical and atypical EAgEC were not detected (p > 0.05). Genes associated with ExPEC were present in all strains isolated from urine samples and in 45 strains (75%) isolated from stool samples. Coproisolates belonged to 10 serogroups and 13 serovars: O3:H2, O11:H10, O16:H48, O51:H30, O55:H21, O73:H18, O73:H33, O86:H2, O86:H10, O92:H33, O140:H2, O159:H10. Two strains had unique nucleotide sequences of genes encoding O-antigens that were missing from the SerotypeFinder database. 80% of EAgEC isolated from feces and urine was characterized by an enteroaggregative/uropathogenic genotype (EAgEC/UPEC). Most of the strains isolated from urine belonged to the virulent clone of high-risk epidemic spread ST 38 associated with hybrid strains of UPEC / EAgEC.

Comparative analysis of virulence determinants, phylogroups, and antibiotic susceptibility patterns of typical versus atypical Enteroaggregative E. coli in India

Enteroaggregative Escherichia coli (EAEC) is an evolving enteric pathogen that causes acute and chronic diarrhea in developed and industrialized nations in children. EAEC epidemiology and the importance of atypical EAEC (aEAEC) isolation in childhood diarrhea are not well documented in the Indian setting. A comparative analysis was undertaken to evaluate virulence, phylogeny, and antibiotic sensitivity among typical tEAEC versus aEAEC. A total of 171 EAEC isolates were extracted from a broad surveillance sample of diarrheal (N = 1210) and healthy children (N = 550) across North India. Polymerase chain reaction (PCR) for the aggR gene (master regulator gene) was conducted to differentiate tEAEC and aEAEC. For 21 virulence genes, we used multiplex PCR to classify possible virulence factors among these strains. Phylogenetic classes were identified by a multiplex PCR for chuA, yjaA, and a cryptic DNA fragment, TspE4C2. Antibiotic susceptibility was conducted by the disc diffusion method as per CLSI guidelines. EAEC was associated with moderate to severe diarrhea in children. The prevalence of EAEC infection (11.4%) was higher than any other DEC group (p = 0.002). tEAEC occurrence in the diarrheal group was higher than in the control group (p = 0.0001). tEAEC strain harbored more virulence genes than aEAEC. astA, aap, and aggR genes were most frequently found in the EAEC from the diarrheal population. Within tEAEC, this gene combination was present in more than 50% of strains. Also, 75.8% of EAEC strains were multidrug-resistant (MDR). Phylogroup D (43.9%) and B1 (39.4%) were most prevalent in the diarrheal and control group, respectively. Genetic analysis revealed EAEC variability; the comparison of tEAEC and aEAEC allowed us to better understand the EAEC virulence repertoire. Further microbiological and epidemiological research is required to examine the pathogenicity of not only typical but also atypical EAEC.

Enteroaggregative E. coli (EAEC) are an increasingly important cause of diarrhea. E. coli belonging to this category cause watery diarrhea, which is often persistent and can be inflammatory. It is also associated with traveler’s diarrhea in children and adults in middle and high-income countries. EAEC are defined by their ability to adhere to epithelial cells in a characteristic stacked brick-like pattern. However, the identification of these pathogenic strains remains elusive because of its heterogeneous nature. Genes that could contribute to the pathogenicity of EAEC encode adhesions, toxins, and other factors. Due to the heterogeneity of EAEC strains and differing host immune responses, not all EAEC infections are symptomatic. A critical factor in both recognizing EAEC pathogenesis and defining typical EAEC (tEAEC) strains is AggR, a transcriptional control for many EAEC virulence genes. The central role of aggR in virulence confers a strong priority to understand its pathogenicity. To identify EAEC, the CVD432 probe has been used. The CVD432 is a DNA probe from pAA plasmid of EAEC, has been reported to be specific for the detection of EAEC. The lack of sensitivity comes from the genetic heterogeneity of the EAEC strains and the wide geographic dispersal of strains. In our study, we performed a large surveillance of EAEC from North India among the pediatric population. Samples were collected by the microbiology staff at the Postgraduate Institute of Medical Education and Research (PGIMER) and referral system labs in Chandigarh (Manimajra), Punjab (Ludhiana), Haryana (Panchkula and Ambala Cantt), Himachal Pradesh (Hamirpur, Shimla, and Tanda), and Uttarakhand (Rishikesh, Rudrapur, and Haridwar)]. PGIMER is the largest tertiary care hospital in North India and serves patients from across Punjab, Jammu and Kashmir, Himachal Pradesh and Haryana. EAEC infections were detected using molecular methods. In our finding, astA, aap, and aggR genes were most frequently found in the EAEC from the diarrheal population. Within tEAEC, this gene combination is present in more than 50% of strains and helps to differentiate tEAEC from aEAEC. Our collection of EAEC strains helps in finding an appropriate marker for the early detection of EAEC. Our signature sequence (astA, aap, and aggR) will be ideal as focus genes for EAEC identification, as well as tEAEC and aEAEC. The multidrug resistance (MDR) was observed in 75.8% of the EAEC strains. tEAEC exhibits resistance to a greater number of antibiotics with respect to aEAEC. The phylogenetic analysis revealed that EAEC phylogeny is diverse and dispersed in all the phylogroups.

Characterization of a novel AraC/XylS-regulated family of N-acyltransferases in pathogens of the order Enterobacterales

Enteroaggregative Escherichia coli (EAEC) is a diarrheagenic pathotype associated with traveler’s diarrhea, foodborne outbreaks and sporadic diarrhea in industrialized and developing countries. Regulation of virulence in EAEC is mediated by AggR and its negative regulator Aar. Together, they control the expression of at least 210 genes. On the other hand, we observed that about one third of Aar-regulated genes are related to metabolism and transport. In this study we show the AggR/Aar duo controls the metabolism of lipids. Accordingly, we show that AatD, encoded in the AggR-regulated aat operon (aatPABCD) is an N-acyltransferase structurally similar to the essential Apolipoprotein N-acyltransferase Lnt and is required for the acylation of Aap (anti-aggregation protein). Deletion of aatD impairs post-translational modification of Aap and causes its accumulation in the bacterial periplasm. trans-complementation of 042aatD mutant with the AatD homolog of ETEC or with the N-acyltransferase Lnt reestablished translocation of Aap. Site-directed mutagenesis of the E207 residue in the putative acyltransferase catalytic triad disrupted the activity of AatD and caused accumulation of Aap in the periplasm due to reduced translocation of Aap at the bacterial surface. Furthermore, Mass spectroscopy revealed that Aap is acylated in a putative lipobox at the N-terminal of the mature protein, implying that Aap is a lipoprotein. Lastly, deletion of aatD impairs bacterial colonization of the streptomycin-treated mouse model. Our findings unveiled a novel N-acyltransferase family associated with bacterial virulence, and that is tightly regulated by AraC/XylS regulators in the order Enterobacterales.

Although the regulatory scheme of AggR is well understood, the biological relevance of half of AggR-regulated proteins remains unknown. In this study we provide experimental evidence that the AggR-regulated AatD is a novel N-acyltransferase restricted to pathogens of the order Enterobacterales, including EAEC, ETEC, Yersinia sp., and C. rodentium. AatD is structurally similar to Lnt. However, unlike Lnt which is essential for cellular functions, AatD is a dedicated N-acyltransferase required for post-translational modification of virulence factors. Aap was identified as a lipoprotein acylated by AatD. Lipid modification in Aap provides an important post-translational mechanism to regulate the trafficking, stability and subcellular localization of Aap. In the absence of AatD, Aap is retained in the periplasmic space and cannot be translocated to the bacterial surface, presumably, restricting the biological function of the protein. Our data suggest that AggR and Aar virulence regulators, not only regulate the expression of Aap virulence factor at the transcriptional level, but also regulate translocation of Aap to the bacterial surface, which is required for full virulence of EAEC, unveiling an important mechanism of virulence regulation.

Mucus layer modeling of human colonoids during infection with enteroaggragative E. coli

EAEC is a common cause of diarrheal illness worldwide. Pathogenesis is believed to occur in the ileum and colon, where the bacteria adhere and form a robust aggregating biofilm. Among the multiple virulence factors produced by EAEC, the Pic serine protease has been implicated in bacterial colonization by virtue of its mucinolytic activity. Hence, a potential role of Pic in mucus barrier disruption during EAEC infection has been long postulated. In this study, we used human colonoids comprising goblet cells and a thick mucin barrier as an intestinal model to investigate Pic's roles during infection with EAEC. We demonstrated the ability of purified Pic, but not a protease defective Pic mutant to degrade MUC2. Western blot and confocal microscopy analysis revealed degradation of the MUC2 layer in colonoids infected with EAEC, but not with its isogenic EAECpic mutant. Wild-type and MUC2-knockdown colonoids infected with EAEC strains exposed a differential biofilm distribution, greater penetration of the mucus layer and increased colonization of the colonic epithelium by Wild-type EAEC than its isogenic Pic mutant. Higher secretion of pro-inflammatory cytokines was seen in colonoids infected with EAEC than EAECpic. Although commensal E. coli expressing Pic degraded MUC2, it did not show improved mucus layer penetration or colonization of the colonic epithelium. Our study demonstrates a role of Pic in MUC2 barrier disruption in the human intestine and shows that colonoids are a reliable system to study the interaction of pathogens with the mucus layer.

Dual Function of Aar, a Member of the New AraC Negative Regulator Family, in Escherichia coli Gene Expression

Enteroaggregative Escherichia coli (EAEC) is an E. coli pathotype associated with diarrhea and growth faltering. EAEC virulence gene expression is controlled by the autoactivated AraC family transcriptional regulator, AggR. AggR activates transcription of a large number of virulence genes, including Aar, which in turn acts as a negative regulator of AggR itself. Aar has also been shown to affect expression of E. coli housekeeping genes, including H-NS, a global regulator that acts at multiple promoters and silences AT-rich genes (such as those in the AggR regulon). Although Aar has been shown to bind both AggR and H-NS in vitro, functional significance of these interactions has not been shown in vivo In order to dissect this regulatory network, we removed the complex interdependence of aggR and aar by placing the genes under the control of titratable promoters. We measured phenotypic and genotypic changes on downstream genes in EAEC strain 042 and E. coli K-12 strain DH5α, which lacks the AggR regulon. In EAEC, we found that low expression of aar increases aafA fimbrial gene expression via H-NS; however, when aar is more highly expressed, it acts as a negative regulator via AggR. In DH5α, aar affected expression of E. coli genes in some cases via H-NS and in some cases independent of H-NS. Our data support the model that Aar interacts in concert with AggR, H-NS, and possibly other regulators and that these interactions are likely to be functionally significant in vivo.

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

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.

Antibiotic resistance and molecular characterization of enteroaggregative Escherichia coli isolated from patients with diarrhea in the Eastern Province of Saudi Arabia

Aim

To investigate presence of Enteroaggregative Escherichia coli (EAEC) in patients suffering with diarrhea by targeting the pCVD432 (pAA) gene using PCR.

Methods

There were 63 non-duplicate isolates of E. coli isolated from diarrheal cases in teaching hospital in Eastern Province of Saudi Arabia between May 2013 to July 2014. All E. coli strains were examined for antibiotic susceptibility testing and polymerase chain reaction (PCR) for detection of virulence gene markers for EAEC.

Results

Of the 63 E coli strains that were reported with diarrheal cases, 35 (55.6%) EAEC were tested positive for pCVD432 gene and aggR gene was present in 19 (54.3%) strains. All strains tested positive for pCVD432 and aggR genes were classified as typical EAEC (tEAEC). EAEC revealed resistance to tetracycline, ampicillin, nalidixic acid, trimethoprim sulfamethoxazole, ciprofloxacin, streptomycin, noroxin, and piperacillin.

Conclusion

EAEC was detected for the first time, among Saudi patients with diarrhea in this region of Saudi Arabia. The reported antibiotic resistance in this study is considered high among isolated EAEC strains to routinely prescribed antibiotics in our area.

Human Enteric Pathogens in Eight Rivers Used as Rural Household Drinking Water Sources in the Northern Region of South Africa

People living in rural areas still rely on the use of environmental water that is contaminated by human and animal activities. This study assessed the occurrence of human enteric pathogens in rivers that are used by rural communities Vhembe District of South Africa as a source of drinking water covering two seasons (winter and summer) over a one-year period. Water quality was assessed using physico characteristics and indicator organisms (total coliforms, E. coli, Clostridium perfringens). Pathogens tested included bacteria (Pathogenic E. coli, Salmonella-, Shigella- and Vibrio spp.), protozoa (Cryptosporidium- and Giardia spp.), and enteric viruses (Rota-, Noro-, Entero-, and Adenoviruses) while using published molecular protocols. The results showed that the indicator bacteria counts exceeded South African drinking water quality guideline limits and pathogenic E. coli was detected in the samples. No Shigella spp. were isolated, while Vibrio spp. and Salmonella spp. were present; parasites were detected in four rivers and Enteric viruses were predominantly detected in the winter season. The results indicated the poor condition of water and the potential health risks to consumers highlighting the need for implementing river catchment management strategies for continued sustainability in these rivers.

EAST1 toxin: An enigmatic molecule associated with sporadic episodes of diarrhea in humans and animals

EAST1 is produced by a subset of enteroaggregative Escherichia coli strains. This toxin is a 38-amino acid peptide of 4100 Da. It shares 50% homology with the enterotoxic domain of STa and interacts with the same receptor. The mechanism of action of EAST1is proposed to be identical to that of STa eliciting a cGMP increase. EAST1 is associated with diarrheal disease in Man and various animal species including cattle and swine. Nevertheless, as EAST1-positive strains as well as culture supernatants did not provoke unequivocally diarrhea either in animal models or in human volunteers, the role of this toxin in disease is today still debated. This review intent is to examine the role of EAST1 toxin in diarrheal illnesses.

TLR4 Participates in the Inflammatory Response Induced by the AAF/II Fimbriae From Enteroaggregative Escherichia coli on Intestinal Epithelial Cells

Enteroaggregative Escherichia coli (EAEC) infections are one of the most frequent causes of persistent diarrhea in children, immunocompromised patients and travelers worldwide. The most prominent colonization factors of EAEC are aggregative adherence fimbriae (AAF). EAEC prototypical strain 042 harbors the AAF/II fimbriae variant, which mediates adhesion to intestinal epithelial cells and participates in the induction of an inflammatory response against this pathogen. However, the mechanism and the cell receptors implicated in eliciting this response have not been fully characterized. Since previous reports have shown that TLR4 recognize fimbriae from different pathogens, we evaluated the role of this receptor in the response elicited against EAEC by intestinal cells. Using a mutual antagonist against TLR2 and TLR4 (OxPAPC), we observed that blocking of these receptors significantly reduces the secretion of the inflammatory marker IL-8 in response to EAEC and AAF/II fimbrial extract in HT-29 cells. Using a TLR4-specific antagonist (TAK-242), we observed that the secretion of this cytokine was significantly reduced in HT-29 cells infected with EAEC or incubated with AAF/II fimbrial extract. We evaluated the participation of AAF/II fimbriae in the TLR4-mediated secretion of 38 cytokines, chemokines, and growth factors involved in inflammation. A reduction in the secretion of IL-8, GRO, and IL-4 was observed. Our results suggest that TLR4 participates in the secretion of several inflammation biomarkers in response to AAF/II fimbriae.

Enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC, formerly known as "EAggEC") cause acute or persistent watery diarrhoea (with or without mucus) in children, predominantly in low-income countries, and are associated with travellers' diarrhoea in children and adults in middle and high income countries. The diverse nature of EAEC is such that not all strains cause disease. Conversely, certain strains of EAEC possess additional virulence determinants associated with the ability to cause severe diarrhoea and other symptoms, which might be life-threatening in vulnerable patients. The EAEC virulence factors described to date are either encoded on the large virulence plasmid of EAEC (plasmid of aggregative adherence) or on pathogenicity islands on the chromosome. Testing of food and faecal samples involves the detection of EAEC-associated traits in the matrix followed by isolation of the organism and confirmation of the presence of EAEC-associated genes using PCR. The variability of the plasmid structure and virulence gene sequences and the possibility that this mobile genetic element may be lost has necessitated the inclusion of chromosomal markers in the molecular screening assays. There is evidence in the literature of foodborne transmission of EAEC, but currently no evidence of a zoonotic reservoir. Fimbriae-mediated adhesion and biofilm formation are likely to be involved in both clinical manifestations of infection and attachment to foodstuffs. Multidrug resistance appears to be common in EAEC and geographically widespread. Whole-genome sequencing has revealed the mosaic genomic structure of EAEC and provided evidence that horizontal gene transfer and recombination are the driving force for acquisition of novel genome features and potentially novel pathogenic mechanisms. This has significant public health implications in terms of the diversity and pathogenesis of EAEC and its ability to colonise and cause disease in the human host.

Impact of Childhood Nutritional Status on Pathogen Prevalence and Severity of Acute Diarrhea

Children with acute and chronic malnutrition are at increased risk of morbidity and mortality following a diarrheal episode. To compare diarrheal disease severity and pathogen prevalence among children with and without acute and chronic malnutrition, we conducted a cross-sectional study of human immunodeficiency virus-uninfected Kenyan children aged 6–59 months, who presented with acute diarrhea. Children underwent clinical and anthropometric assessments and provided stool for bacterial and protozoal pathogen detection. Clinical and microbiological features were compared using log binomial regression among children with and without wasting (mid-upper arm circumference ≤ 125 mm) or stunting (height-for-age z score ≤ −2). Among 1,363 children, 7.0% were wasted and 16.9% were stunted. After adjustment for potential confounders, children with wasting were more likely than nonwasted children to present with at least one Integrated Management of Childhood Illness danger sign (adjusted prevalence ratio [aPR]: 1.3, 95% confidence interval [CI]: 1.0 to 1.5, P = 0.05), severe dehydration (aPR: 2.4, 95% CI: 1.5 to 3.8, P < 0.01), and enteroaggregative Escherichia coli recovered from their stool (aPR: 1.8, 1.1–2.8, P = 0.02). There were no differences in the prevalence of other pathogens by wasting status after confounder adjustment. Stunting was not associated with clinical severity or the presence of specific pathogens. Wasted children with diarrhea presented with more severe disease than children without malnutrition which may be explained by a delay in care-seeking or diminished immune response to infection. Combating social determinants and host risk factors associated with severe disease, rather than specific pathogens, may reduce the disparities in poor diarrhea-associated outcomes experienced by malnourished children.

Persistent diarrhea: a persistent infection with enteropathogens or a gut commensal dysbiosis?

In children from developing countries 5-10% of acute diarrhea (AD) episodes develop into persistent diarrhea (PD) defined by > 14 days of diarrhea duration. PD represents a major health burden leading to growth faltering. It is also associated with half of all diarrhea mortality. A rational intervention is thus crucial, but depends on an understanding of the pathogenesis of PD, which is still lacking. Many surveys were conducted in Latin America and in South Asia; they differ, however, with respect to enteropathogens associated with PD. Enteroaggregative strains of Escherichia coli (EAEC) were identified by several studies, but they may reflect selection by the frequent antibiotic use during the preceding AD episode. Epidemiologists have in fact identified antibiotic misuse as a major risk factor for PD. Together with the effectiveness of empirical treatment based on nutritional interventions with lactose-reduced and lactose-free diets and particularly complex plant polysaccharides from green banana, one might suspect a role of commensal gut microbiota dysbiosis instead of a persistent infection with enteropathogens in many PD cases. An analysis of the commensal gut microbiota development in persistent diarrhea during nutritional interventions is likely to increase our understanding of PD pathogenesis.

The AraC Negative Regulator family modulates the activity of histone-like proteins in pathogenic bacteria

The AraC Negative Regulators (ANR) comprise a large family of virulence regulators distributed among diverse clinically important Gram-negative pathogens, including Vibrio spp., Salmonella spp., Shigella spp., Yersinia spp., Citrobacter spp., and pathogenic E. coli strains. We have previously reported broad effects of the ANR members on regulators of the AraC/XylS family. Here, we interrogate possible broader effects of the ANR members on the bacterial transcriptome. Our studies focused on Aar (AggR-activated regulator), an ANR family archetype in enteroaggregative E. coli (EAEC) isolate 042. Transcriptome analysis of EAEC strain 042, 042aar and 042aar(pAar) identified more than 200 genes that were differentially expressed (+/- 1.5 fold, p<0.05). Most of those genes are located on the bacterial chromosome (195 genes, 92.85%), and are associated with regulation, transport, metabolism, and pathogenesis, based on the predicted annotation; a considerable number of Aar-regulated genes encoded for hypothetical proteins (46 genes, 21.9%) and regulatory proteins (25, 11.9%). Notably, the transcriptional expression of three histone-like regulators, H-NS (orf1292), H-NS homolog (orf2834) and StpA, was down-regulated in the absence of aar and may explain some of the effects of Aar on gene expression. By employing a bacterial two-hybrid system, LacZ reporter assays, pull-down and electrophoretic mobility shift assay (EMSA) analysis, we demonstrated that Aar binds directly to H-NS and modulates H-NS-induced gene silencing. Importantly, Aar was highly expressed in the mouse intestinal tract and was found to be necessary for maximal H-NS expression. In conclusion, this work further extends our knowledge of genes under the control of Aar and its biological relevance in vivo.

The AraC Negative Regulators (ANR) is a large family of negative regulators distributed in several clinically relevant Gram-negative pathogens, including Vibrio spp., Salmonella spp., Shigella spp., Yersinia spp., Citrobacter spp., pathogenic E. coli, and members of the Pasteurellaceae. Previously, we showed that the ANR family suppresses transcriptional expression of virulence factors such as fimbriae, toxins, and the type VI secretion system by directly down-regulating AraC/XylS master regulators. Transcriptome and biochemical analysis of Aar (AggR-activated regulator), an ANR family archetype in enteroaggregative E. coli (EAEC) 042, demonstrated that Aar binds directly to H-NS and modulates the H-NS-induced gene expression. Accordingly, mutation of aar decreased expression of the H-NS-regulated Lpf fimbriae, LPS-related enzymes, GadXW operon and porins. Importantly, Aar was highly expressed in the mouse intestinal tract and was found to be necessary for maximal H-NS expression. These findings unveil an exquisite regulatory network in pathogenic bacteria, which operates by concomitant control of master transcriptional regulators of the AraC family and global negative H-NS regulators.

Epidemiology of enteroaggregative Escherichia coli infections and associated outcomes in the MAL-ED birth cohort

Background

Enteroaggregative E. coli (EAEC) have been associated with mildly inflammatory diarrhea in outbreaks and in travelers and have been increasingly recognized as enteric pathogens in young children with and without overt diarrhea. We examined the risk factors for EAEC infections and their associations with environmental enteropathy biomarkers and growth outcomes over the first two years of life in eight low-resource settings of the MAL-ED study.

Methods

EAEC infections were detected by PCR gene probes for aatA and aaiC virulence traits in 27,094 non-diarrheal surveillance stools and 7,692 diarrheal stools from 2,092 children in the MAL-ED birth cohort. We identified risk factors for EAEC and estimated the associations of EAEC with diarrhea, enteropathy biomarker concentrations, and both short-term (one to three months) and long-term (to two years of age) growth.

Results

Overall, 9,581 samples (27.5%) were positive for EAEC, and almost all children had at least one detection (94.8%) by two years of age. Exclusive breastfeeding, higher enrollment weight, and macrolide use within the preceding 15 days were protective. Although not associated with diarrhea, EAEC infections were weakly associated with biomarkers of intestinal inflammation and more strongly with reduced length at two years of age (LAZ difference associated with high frequency of EAEC detections: -0.30, 95% CI: -0.44, -0.16).

Conclusions

Asymptomatic EAEC infections were common early in life and were associated with linear growth shortfalls. Associations with intestinal inflammation were small in magnitude, but suggest a pathway for the growth impact. Increasing the duration of exclusive breastfeeding may help prevent these potentially inflammatory infections and reduce the long-term impact of early exposure to EAEC.

Enteroaggregative E. coli (EAEC) are pathogens that infect the intestine and can cause diarrhea. They are also commonly identified among young children in low-resource settings, who can carry the pathogen without symptomatic diarrhea. We examined the risk factors for EAEC infections and their associations with child health outcomes over the first two years of life in eight low-resource settings of the MAL-ED study. EAEC infections were detected using molecular methods in more than 30,000 stools collected from 2,092 children in the MAL-ED study. We identified risk factors for EAEC and estimated the associations of EAEC with diarrhea, markers of intestinal health, and child growth. Almost all children were infected with EAEC at least once by two years of age. Exclusive breastfeeding, higher enrollment weight, and recent macrolide antibiotic use were protective against these infections. Although not associated with diarrhea in these children, EAEC infections were associated with intestinal inflammation and reduced length at two years of age. EAEC may impact child development, even in the absence of diarrhea, by causing intestinal inflammation and impairing child growth.

The Role of Fibronectin in the Adherence and Inflammatory Response Induced by Enteroaggregative Escherichia coli on Epithelial Cells

Enteroaggregative Escherichia coli (EAEC) infections are still one of the most important etiologic pathogens of diarrhea in children worldwide. EAEC pathogenesis comprises three stages: adherence and colonization, production of toxins, and diarrhea followed by inflammation. Previous studies have demonstrated that EAEC strains have the ability to bind to fibronectin (FN); however, the role this extracellular matrix protein plays in the inflammatory response induced by EAEC remains unknown. In this study, we postulated that FN-mediated adherence of EAEC strains to epithelial cells increases the expression of pro-inflammatory genes. To verify this hypothesis, we infected HEp-2 and HT-29 cells, in both the presence and absence of FN, with EAEC reference strain 042. We quantified IL-8 secretion and the relative expression of a set of genes regulated by the NF-κB pathway. Although FN increased EAEC adherence, no changes in IL-8 protein secretion or IL8 gene expression were observed. Similar observations were found in HEp-2 cells transfected with FN-siRNA and infected with EAEC. To evaluate the involvement of AAF/II fimbriae, we infected HEp-2 and HT-29 cells, in both the presence and absence of FN, with an EAEC 042aafA mutant strain transformed with a plasmid harboring the native aafA gene with a site-directed mutation in Lys72 residue (K72A and K72R strains). No changes in IL-8 secretion were observed. Finally, SEM immunogold assay of cells incubated with FN and infected with EAEC revealed that AAF fimbriae can bind to cells either directly or mediated by FN. Our data suggests that FN participates in AAF/II fimbriae-mediated adherence of EAEC to epithelial cells, but not in the inflammatory response of cells infected by this pathogen.

Diarrheagenic Escherichia coli

Most Escherichia coli strains live harmlessly in the intestines and rarely cause disease in healthy individuals. Nonetheless, a number of pathogenic strains can cause diarrhea or extraintestinal diseases both in healthy and immunocompromised individuals. Diarrheal illnesses are a severe public health problem and a major cause of morbidity and mortality in infants and young children, especially in developing countries. E. coli strains that cause diarrhea have evolved by acquiring, through horizontal gene transfer, a particular set of characteristics that have successfully persisted in the host. According to the group of virulence determinants acquired, specific combinations were formed determining the currently known E. coli pathotypes, which are collectively known as diarrheagenic E. coli. In this review, we have gathered information on current definitions, serotypes, lineages, virulence mechanisms, epidemiology, and diagnosis of the major diarrheagenic E. coli pathotypes.

Colonization of Enteroaggregative Escherichia coli and Shiga toxin-producing Escherichia coli in chickens and humans in southern Vietnam

Background

Enteroaggregative (EAEC) and Shiga-toxin producing Escherichia coli (STEC) are a major cause of diarrhea worldwide. E. coli carrying both virulence factors characteristic for EAEC and STEC and producing extended-spectrum beta-lactamase caused severe and protracted disease during an outbreak of E. coli O104:H4 in Europe in 2011. We assessed the opportunities for E. coli carrying the aggR and stx genes to emerge in ‘backyard’ farms in south-east Asia.

Results

Faecal samples collected from 204 chicken farms; 204 farmers and 306 age- and gender-matched individuals not exposed to poultry farming were plated on MacConkey agar plates with and without antimicrobials being supplemented. Sweep samples obtained from MacConkey agar plates without supplemented antimicrobials were screened by multiplex PCR for the detection of the stx1, stx2 and aggR genes. One chicken farm sample each (0.5 %) contained the stx1 and the aggR gene. Eleven (2.4 %) human faecal samples contained the stx1 gene, 2 samples (0.4 %) contained stx2 gene, and 31 (6.8 %) contained the aggR gene. From 46 PCR-positive samples, 205 E. coli isolates were tested for the presence of stx1, stx2, aggR, wzx_O104 and fliC_H4 genes. None of the isolates simultaneously contained the four genetic markers associated with E. coli O104:H4 epidemic strain (aggR, stx2, wzx_O104 and fliC_H4). Of 34 EAEC, 64.7 % were resistant to 3^rd-generation cephalosporins.

Conclusion

These results indicate that in southern Vietnam, the human population is a more likely reservoir of aggR and stx gene carrying E. coli than the chicken population. However, conditions for transmission of isolates and/or genes between human and animal reservoirs resulting in the emergence of highly virulent E. coli strains are still favorable, given the nature of‘backyard’ farms in Vietnam.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0827-z) contains supplementary material, which is available to authorized users.

Virulence determinants in enteroaggregative Escherichia coli from North India and their interaction in in vitro organ culture system

Enteroaggregative Escherichia coli (EAEC) is an important diarrhoeal pathogen causing diseases in multiple epidemiological and clinical settings. In developing countries like India, diarrhoeal diseases are one of the major killers among paediatric population and oddly, few studies are available from Indian paediatric population on the variability of EAEC virulence genes. In this study, we examined the distribution of plasmid and chromosomal-encoded virulence determinants in EAEC isolates, and analysed cytokines response generated against EAEC with specific aggregative adherence fimbriae (AAF) type in duodenal biopsies using in vitro organ culture (IVOC) mimicking in vivo conditions. Different virulence marker combinations among strains were reflected as a function of specific adhesins signifying EAEC heterogeneity. fis gene emerged as an important genetic marker apart from aggA and aap Further, EAEC infection in IVOC showed upregulation of IL-8, IL-1β, IL-6, TNF-α and TLR-5 expression. EAEC with AAFII induced significant TLR-5 and IL-8 response, conceivably owing to more pathogenicity markers. This study sheds light on the pattern of EAEC pathotypes prevalent in North Indian paediatric population and highlights the presence of unique virulence combinations in pathogenic strains. Thus, evident diversity in EAEC virulence and multifaceted bacteria-host crosstalk can provide useful insights for the strategic management of diarrhoeal diseases in India, where diarrhoeal outbreaks are more frequent.

Association between aggregative adherence fimbriae types including putative new variants and virulence-related genes and clump formation among aggR-positive Escherichia coli strains isolated in Thailand and Japan

Enteroaggregative Escherichia coli (EAggEC) are an important cause of diarrhea. Four types of AAF have been identified; however, their prevalence and association with virulence properties remain unclear. E. coli strains carrying the aggR gene as EAggEC that were isolated in Japan and Thailand (n = 90) were examined for AAF subunit genes, two toxin genes (pet/astA), and clump formation. The most prevalent AAF gene was hdaA (28%), followed by aafA (20%), aggA (12%), and agg3A (4%), as well as a putative new AAF sequence (25.6%). Retention status of the toxin genes and intensities of clump formation appeared to vary according to the AAF type.

Involvement of main diarrheagenic Escherichia coli, with emphasis on enteroaggregative E. coli, in severe non-epidemic pediatric diarrhea in a high-income country

Background

Bacterial and viral enteric pathogens are the leading cause of diarrhea in infants and children. We aimed to identify and characterize the main human diarrheagenic E. coli (DEC) in stool samples obtained from children less than 5 years of age, hospitalized for acute gastroenteritis in Israel, and to examine the hypothesis that co-infection with DEC and other enteropathogens is associated with the severity of symptoms.

Methods

Stool specimens obtained from 307 patients were tested by multiplex PCR (mPCR) to identify enteroaggregative E. coli (EAEC), enterohemorrhagic (EHEC), enteropathogenic E. coli (EPEC) and enterotoxigenic E. coli (ETEC). Specimens were also examined for the presence of rotavirus by immunochromatography, and of Shigella, Salmonella and Campylobacter by stool culture; clinical information was also obtained.

Results

Fifty nine (19%) children tested positive for DEC; EAEC and atypical EPEC were most common, each detected in 27 (46%), followed by ETEC (n = 3; 5%), EHEC and typical EPEC (each in 1 child; 1.5%). Most EAEC isolates were resistant to cephalexin, cefixime, cephalothin and ampicillin, and genotypic characterization of EAEC isolates by O-typing and pulsed-field gel electrophoresis showed possible clonal relatedness among some. The likelihood of having > 10 loose/watery stools on the most severe day of illness was significantly increased among patients with EAEC and rotavirus co-infection compared to children who tested negative for both pathogens: adjusted odds ratio 7.0 (95% CI 1.45-33.71, P = 0.015).

Conclusion

DEC was common in this pediatric population, in a high-income country, and mixed EAEC and rotavirus infection was characterized by especially severe diarrhea.

Novel aggregative adherence fimbria variant of enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) organisms belong to a diarrheagenic pathotype known to cause diarrhea and can be characterized by distinct aggregative adherence (AA) in a stacked-brick pattern to cultured epithelial cells. In this study, we investigated 118 EAEC strains isolated from the stools of Danish adults with traveler's diarrhea. We evaluated the presence of the aggregative adherence fimbriae (AAFs) by a multiplex PCR, targeting the four known major subunit variants as well as their usher-encoding genes. Almost one-half (49/118) of the clinical isolates did not possess any known AAF major fimbrial subunit, despite the presence of other AggR-related loci. Further investigation revealed the presence of an AAF-related gene encoding a yet-uncharacterized adhesin, termed agg5A. The sequence of the agg5DCBA gene cluster shared fimbrial accessory genes (usher, chaperone, and minor pilin subunit genes) with AAF/III, as well as the signal peptide present in the beginning of the agg3A gene. The complete agg5DCBA gene cluster from a clinical isolate, EAEC strain C338-14, with the typical stacked-brick binding pattern was cloned, and deletion of the cluster was performed. Transformation to a nonadherent E. coli HB101 and complementation of the nonadherent C338-14 mutant with the complete gene cluster restored the AA adhesion. Overall, we found the agg5A gene in 12% of the 118 strains isolated from Denmark, suggesting that this novel adhesin represents an important variant.

HilA-like regulators in Escherichia coli pathotypes: the YgeH protein from the enteroaggregative strain 042

Background

The HilA protein is the master regulator of the Salmonella pathogenicity island 1 (SPI1). EilA and YgeH proteins show a moderate similarity to HilA and are encoded in pathogenicity islands from several E. coli strains, both pathogenic and non-pathogenic. In the present work we characterize the YgeH protein from the enteroaggregative E. coli strain 042 (locus tag EC042_3050).

Results

We show that both E. coli 042 YgeH and EilA proteins are able to functionally replace HilA in Salmonella. Interestingly, this is not the rule for all YgeH proteins: the YgeH protein from the enterohaemorragic E. coli strain O157 appears to be non-functional. ygeH expression is not influenced by growth osmolarity or temperature, and moderately increases in cells entering the stationary phase. H-NS represses ygeH expression under all growth conditions tested, and binds with specificity to the ygeH promoter region. As expected, expression of ETT2 (Escherichia coli type 3 secretion system 2) genes requires YgeH: ETT2 operons are downregulated in a ygeH mutant. Accordingly, since H-NS represses ygeH expression, ETT2 expression is significantly increased in an hns mutant.

Conclusion

E. coli 042 YgeH protein is functional and able to replace HilA in Salmonella. ETT2 gene expression requires YgeH activity which, in turn, is subjected to H-NS silencing.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-014-0268-5) contains supplementary material, which is available to authorized users.

A sensitive and specific molecular tool for detection of both typical and atypical enteroaggregative Escherichia coli

A multiplex PCR has been standardized and evaluated for the identification of both typical and atypical enteroaggregative Escherichia coli (EAEC). The assay detecting aaiA, aaiG, aggR and aatA presented 94.8% of sensitivity, 94.3% of specificity and was able to efficiently detect both groups of EAEC among E. coli isolated from stool cultures.

Whole genome sequence comparison of vtx2-converting phages from Enteroaggregative Haemorrhagic Escherichia coli strains

Background

Enteroaggregative Haemorrhagic E. coli (EAHEC) is a new pathogenic group of E. coli characterized by the presence of a vtx2-phage integrated in the genomic backbone of Enteroaggregative E. coli (EAggEC). So far, four distinct EAHEC serotypes have been described that caused, beside the large outbreak of infection occurred in Germany in 2011, a small outbreak and six sporadic cases of HUS in the time span 1992–2012. In the present work we determined the whole genome sequence of the vtx2-phage, termed Phi-191, present in the first described EAHEC O111:H2 isolated in France in 1992 and compared it with those of the vtx-phages whose sequences were available.

Results

The whole genome sequence of the Phi-191 phage was identical to that of the vtx2-phage P13374 present in the EAHEC O104:H4 strain isolated during the German outbreak 20 years later. Moreover, it was also almost identical to those of the other vtx2-phages of EAHEC O104:H4 strains described so far. Conversely, the Phi-191 phage appeared to be different from the vtx2-phage carried by the EAHEC O111:H21 isolated in the Northern Ireland in 2012.

The comparison of the vtx2-phages sequences from EAHEC strains with those from the vtx-phages of typical Verocytotoxin-producing E. coli strains showed the presence of a 900 bp sequence uniquely associated with EAHEC phages and encoding a tail fiber.

Conclusions

At least two different vtx2-phages, both characterized by the presence of a peculiar tail fiber-coding gene, intervened in the emergence of EAHEC. The finding of an identical vtx2-phage in two EAggEC strains isolated after 20 years in spite of the high variability described for vtx-phages is unexpected and suggests that such vtx2-phages are kept under a strong selective pressure.

The observation that different EAHEC infections have been traced back to countries where EAggEC infections are endemic and the treatment of human sewage is often ineffective suggests that such countries may represent the cradle for the emergence of the EAHEC pathotype. In these regions, EAggEC of human origin can extensively contaminate the environment where they can meet free vtx-phages likely spread by ruminants excreta.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-574) contains supplementary material, which is available to authorized users.

X-ray crystal structure of the passenger domain of plasmid encoded toxin(Pet), an autotransporter enterotoxin from enteroaggregative Escherichia coli (EAEC)

Autotransporters (ATs) represent a superfamily of proteins produced by a variety of pathogenic bacteria, which include the pathogenic groups of Escherichia coli (E. coli) associated with gastrointestinal and urinary tract infections. We present the first X-ray structure of the passenger domain from the Plasmid-encoded toxin (Pet) a 100 kDa protein at 2.3 Å resolution which is a cause of acute diarrhea in both developing and industrialized countries. Pet is a cytoskeleton-altering toxin that induces loss of actin stress fibers. While Pet (pdb code: 4OM9) shows only a sequence identity of 50% compared to the closest related protein sequence, extracellular serine protease plasmid (EspP) the structural features of both proteins are conserved. A closer structural look reveals that Pet contains a β-pleaded sheet at the sequence region of residues 181-190, the corresponding structural domain in EspP consists of a coiled loop. Secondary, the Pet passenger domain features a more pronounced beta sheet between residues 135 and 143 compared to the structure of EspP.

Diarrheagenic enteroaggregative Escherichia coli causing urinary tract infection and bacteremia leading to sepsis

We report a case of a 55-year-old immunocompromised female who presented to the emergency department with severe diarrhea and vomiting following travel to the Philippines. Stool bacteriology revealed a mixed infection involving an enteropathogenic Escherichia coli and two distinct strains of enteroaggregative Escherichia coli (EAEC). During hospitalization, urine and blood culture tested positive for one of the diarrheagenic EAEC strains, necessitating urinary catheterization, intensive care, and antimicrobial treatment with trimethoprim-sulfamethoxazole, followed by meropenem. Although known to occasionally cause urinary tract infections, EAEC have not been previously associated with sepsis. Our report highlights the potential of EAEC to cause severe extraintestinal infections.

Inflammatory diarrhea due to enteroaggregative Escherichia coli: evidence from clinical and mice model studies

BACKGROUND

This study was conducted to determine the role of enteroaggregative Escherichia coli (EAEC) in inflammatory diarrhea among hospitalized patients in Kolkata. The inflammatory pathogenesis of EAEC was established in mice model and histopathological studies. Presence of fecal leucocytes (FLCs) can be suspected for EAEC infection solely or as a mixed with other enteric pathogens.

METHODS

Active surveillance was conducted for 2 years on 2 random days per week with every 5th patient admitted to the Infectious Diseases Hospital (IDH). Diarrheal samples were processed by conventional culture, microscopy, ELISA and molecular methods. Two EAEC isolated as sole pathogens were examined in mice after induced intestinal infection. The intestinal tissue samples were processed to analyze the histological changes.

RESULTS

Of the 2519 samples screened, fecal leucocytes, erythrocytes and occult blood were detected in 1629 samples. Most of the patients had acute watery diarrhea (75%) and vomiting (78%). Vibrio cholerae O1 was the main pathogen in patients of 5-10 years age group (33%). Shigellosis was more in children from 2-5 years of age (19%), whereas children <2 years appeared to be susceptible for infection caused by EAEC (16%). When tested for the pathogenicity, the EAEC strains colonized well and caused inflammatory infection in the gut mucosa of BALB/C mice.

CONCLUSION

This hospital-based surveillance revealed prevalence of large number of inflammatory diarrhea. EAEC was the suspected pathogen and <2 years children appeared to be the most susceptible age group. BALB/C mice may be a suitable animal model to study the EAEC-mediated pathogenesis.

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

Characteristics of enteroaggregative Escherichia coli isolated from healthy carriers and from patients with diarrhoea

The aim of this study was to compare the virulence characteristics and phylogenetic features of enteroaggregative Escherichia coli (EAEC) strains from adults with and without diarrhoea and to search for associations between the analysed genes and carrier or diarrhoeagenic strains, respectively. Faecal samples of 487 healthy humans were screened for EAEC strains and compared with isolates from diarrhoeal patients. Virulence and virulence-associated gene typing, serotyping, multilocus sequence typing and antibiotic susceptibility testing were performed for characterization of the isolates. Characteristics significantly linked to carrier strains or to diarrhoeagenic strains were determined. From 487 stool samples, 24 EAEC strains were obtained. Comparison with strains originating from diseased persons showed a statistically significant association of the genes sat (P = 0.002) and agg3C (P = 0.0139) with the carrier strains, and of pCVD432 (P = 0.0001), aap (P = 0.003), aggR (P = 0.0048) and air (P = 0.031) with the diarrhoeagenic strains. Our study indicates that a certain subset of EAEC is unrelated to diarrhoea, for which sat and agg3C may be markers. Our results further suggest that diarrhoeagenic EAEC strains are distinguishable from carrier strains and suggest that, in addition to well-established markers such as pCVD432 and aggR, aap and air may be useful additional markers to define EAEC as an aetiological agent of diarrhoea in adults.

Animal models of enteroaggregative Escherichia coli infection

Enteroaggregative Escherichia coli (EAEC) has been acknowledged as an emerging cause of gastroenteritis worldwide for over two decades. Epidemiologists are revealing the role of EAEC in diarrheal outbreaks as a more common occurrence than ever suggested before. EAEC induced diarrhea is most commonly associated with travelers, children and immunocompromised individuals however its afflictions are not limited to any particular demographic. Many attributes have been discovered and characterized surrounding the capability of EAEC to provoke a potent pro-inflammatory immune response, however cellular and molecular mechanisms underlying initiation, progression and outcomes are largely unknown. This limited understanding can be attributed to heterogeneity in strains and the lack of adequate animal models. This review aims to summarize current knowledge about EAEC etiology, pathogenesis and clinical manifestation. Additionally, current animal models and their limitations will be discussed along with the value of applying systems-wide approaches such as computational modeling to study host-EAEC interactions.

Role of efflux pumps in the antibiotic resistance of bacteria embedded in a biofilm

Biofilms are complex microbial associations anchored to abiotic or biotic surfaces, embedded in extracellular matrix produced by the biofilms themselves where they interact with each other and the environment. One of the main properties of biofilms is their capacity to be more resistant to antimicrobial agents than planktonic cells. Efflux pumps have been reported as one of the mechanisms responsible for the antimicrobial resistance in biofilm structures. Evidence of the role of efflux pump in biofilm resistance has been found in several microorganisms such as Pseudomonas aeruginosa, Escherichia coli and Candida albicans. However, in spite of the studies on the importance of efflux pumps in biofilm growth and about their relevance in antimicrobial resistance forming biofilm, the exact role of these efflux systems has not been determined as yet.

Enteroaggregative Escherichia coli strain in a novel weaned mouse model: exacerbation by malnutrition, biofilm as a virulence factor and treatment by nitazoxanide

Enteroaggregative Escherichia coli (EAEC) is increasingly recognized as a common cause of diarrhoea in healthy, malnourished and immune-deficient adults and children. There is no reproducible non-neonatal animal model for longitudinal studies of disease mechanism or therapy. Using two strains of human-derived EAEC to challenge weaned C57BL/6 mice, we explored an in vivo model of EAEC infection in mice, in which disease was monitored quantitatively as the growth rate, stool shedding and tissue burden of organisms; nutritional status was varied, and a new class of therapeutics was assessed. A single oral challenge of EAEC strain 042 resulted in significant growth shortfalls (5-8 % of body weight in 12 days), persistent shedding of micro-organisms in stools [>10(3.2) c.f.u. (10 mg stool)(-1) for at least 14 days] and intestinal tissue burden [~10(3) c.f.u. (10 mg tissue)(-1) detectable up to 14 days post-challenge]. Moderate malnourishment of mice using a 'regional basic diet' containing 7 % protein and reduced fat and micronutrients heightened all parameters of infection. Nitazoxanide in subMIC doses, administered for 3 days at the time of EAEC challenge, lessened growth shortfalls (by >10 % of body weight), stool shedding [by 2-3 logs (10 mg stool)(-1)] and tissue burden of organisms (by >75 % in the jejunum and colon). Thus, weaned C57BL/6 mice challenged with EAEC is a convenient, readily inducible model of EAEC infection with three highly quantifiable outcomes in which disease severity is dependent on the nutritional status of the host, and which is modifiable in the presence of inhibitors of pyruvate ferredoxin oxidoreductase such as nitazoxanide.

The role of peroxisome proliferator-activated receptor γ in immune responses to enteroaggregative Escherichia coli infection

Background

Enteroaggregative Escherichia coli (EAEC) is recognized as an emerging cause of persistent diarrhea and enteric disease worldwide. Mucosal immunity towards EAEC infections is incompletely understood due in part to the lack of appropriate animal models. This study presents a new mouse model and investigates the role of peroxisome proliferator-activated receptor gamma (PPARγ) in the modulation of host responses to EAEC in nourished and malnourished mice.

Methods/Principal Findings

Wild-type and T cell-specific PPARγ null C57BL/6 mice were fed protein-deficient diets at weaning and challenged with 5×10⁹cfu EAEC strain JM221 to measure colonic gene expression and immune responses to EAEC. Antigen-specific responses to E. coli antigens were measured in nourished and malnourished mice following infection and demonstrated the immunosuppressive effects of malnutrition at the cellular level. At the molecular level, both pharmacological blockade and deletion of PPARγ in T cells resulted in upregulation of TGF-β, IL-6, IL-17 and anti-microbial peptides, enhanced Th17 responses, fewer colonic lesions, faster clearance of EAEC, and improved recovery. The beneficial effects of PPARγ blockade on weight loss and EAEC clearance were abrogated by neutralizing IL-17 in vivo.

Conclusions

Our studies provide in vivo evidence supporting the beneficial role of mucosal innate and effector T cell responses on EAEC burden and suggest pharmacological blockade of PPARγ as a novel therapeutic intervention for EAEC infection.

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

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.