Enteroaggregative escherichia coli virulence factors in traveler's diarrhea strains

Highly-conserved regulatory activity of the ANR family in the virulence of diarrheagenic bacteria through interaction with master and global regulators

ANR (AraC negative regulators) are a novel class of small regulatory proteins commonly found in enteric pathogens. Aar (AggR-activated regulator), the best-characterized member of the ANR family, regulates the master transcriptional regulator of virulence AggR and the global regulator HNS in enteroaggregative Escherichia coli (EAEC) by protein-protein interactions. On the other hand, Rnr (RegA-negative regulator) is an ANR homolog identified in attaching and effacing (AE) pathogens, including Citrobacter rodentium and enteropathogenic Escherichia coli (EPEC), sharing only 25% identity with Aar. We previously found that C. rodentium lacking Rnr exhibits prolonged shedding and increased gut colonization in mice compared to the parental strain. To gain mechanistic insights into this phenomenon, we characterized the regulatory role of Rnr in the virulence of prototype EPEC strain E2348/69 by genetic, biochemical, and human organoid-based approaches. Accordingly, RNA-seq analysis revealed more than 500 genes differentially regulated by Rnr, including the type-3 secretion system (T3SS). The abundance of EspA and EspB in whole cells and bacterial supernatants confirmed the negative regulatory activity of Rnr on T3SS effectors. We found that besides HNS and Ler, twenty-six other transcriptional regulators were also under Rnr control. Most importantly, the deletion of aar in EAEC or rnr in EPEC increases the adherence of these pathogens to human intestinal organoids. In contrast, the overexpression of ANR drastically reduces bacterial adherence and the formation of AE lesions in the intestine. Our study suggests a conserved regulatory mechanism and a central role of ANR in modulating intestinal colonization by these enteropathogens despite the fact that EAEC and EPEC evolved with utterly different virulence programs.

Comparative Pathogenomics of Escherichia coli: Polyvalent Vaccine Target Identification through Virulome Analysis

Comparative genomics of bacterial pathogens has been useful for revealing potential virulence factors. Escherichia coli is a significant cause of human morbidity and mortality worldwide but can also exist as a commensal in the human gastrointestinal tract. With many sequenced genomes, it has served as a model organism for comparative genomic studies to understand the link between genetic content and potential for virulence. To date, however, no comprehensive analysis of its complete “virulome” has been performed for the purpose of identifying universal or pathotype-specific targets for vaccine development. Here, we describe the construction of a pathotype database of 107 well-characterized completely sequenced pathogenic and nonpathogenic E. coli strains, which we annotated for major virulence factors (VFs). The data are cross referenced for patterns against pathotype, phylogroup, and sequence type, and the results were verified against all 1,348 complete E. coli chromosomes in the NCBI RefSeq database. Our results demonstrate that phylogroup drives many of the “pathotype-associated” VFs, and ExPEC-associated VFs are found predominantly within the B2/D/F/G phylogenetic clade, suggesting that these phylogroups are better adapted to infect human hosts. Finally, we used this information to propose polyvalent vaccine targets with specificity toward extraintestinal strains, targeting key invasive strategies, including immune evasion (group 2 capsule), iron acquisition (FyuA, IutA, and Sit), adherence (SinH, Afa, Pap, Sfa, and Iha), and toxins (Usp, Sat, Vat, Cdt, Cnf1, and HlyA). While many of these targets have been proposed before, this work is the first to examine their pathotype and phylogroup distribution and how they may be targeted together to prevent disease.

Molecular detection of virulence markers to identify diarrhoeagenic Escherichia coli isolated from Mula-Mutha river, Pune District, India

In this study presence of virulence genes in multidrug resistant Escherichia coli isolated from Mula-Mutha river, Pune, India was undertaken. The objective was to understand whether the isolates were of diarrhoeagenic or of environmental origin. This was essential since the river flows through urban and rural parts of Pune and its water is used not only for industrial and agricultural purposes but also for domestic usage. One hundred and two multidrug E. coli isolates were selected from our previous study which detected genes coding for antibiotic resistance as well as identified integrons associated with multidrug resistance. Isolates were subjected to multiplex PCR to detect presence of virulence genes, set1A, set1B, sen astA, aggA, aafA, pet, stx1 and stx. Sequencing was performed to confirm the amplified PCR product. Seven of the 102 E. coli isolates showed gene set1A alone identifying them as Enteroaggregative E. coli. Thus, the findings revealed that majority of drug resistant E. coli were environmental in origin. The presence of antibiotic resistant genes, integrons in the environment as well as diarrhoeagenic E. coli isolates is a warning and calls for efficient public health measures to ensure that untreated sewage and industrial waste does not enter the Mula-Mutha river.

Typical and Atypical Enteroaggregative Escherichia coli Are Both Virulent in the Galleria mellonella Model

Enteroaggregative Escherichia coli (EAEC) is an emerging pathotype responsible for acute and persistent diarrhea. It can be classified as typical and atypical strains, respectively, based on the presence or absence of the AggR regulon, suggesting a higher virulence for typical EAEC. This study aims to evaluate in the Galleria mellonella model if there are differences in the virulence profiles among clinical strains of typical and atypical EAEC, prototype strains EAEC C1096, 042 and its aggR mutant. The clinical EAEC strains (n = 20) were analyzed for the presence of 22 putative virulence factors of EAEC or extraintestinal E. coli by PCR, as well as phenotypic characteristics of virulence (enzymes, siderophore, and biofilm). The survival of the larvae was analyzed after inoculation of 10⁴-10⁷ CFU/larva; the monitoring of bacterial growth in vivo and hemocyte quantification was determined after inoculation of the prototype strains (10⁵ CFU/larva) at different periods after infection. The strains of typical and atypical EAEC presented the same virulence profile for the larva, regardless of the amount or type of genes and phenotypic aspects of virulence analyzed. In addition, the EAEC 042 aggR mutant strain showed a significant reduction in the mortality of the inoculated larvae compared to the wild-type strain. In conclusion, the results obtained herein demonstrate that the virulence of EAEC seems to be related to the AggR regulon, but not exclusively, and atypical EAEC strains may be as virulent as typical ones in vivo in the G. mellonella model.

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.

The possible role of bacteria, viruses, and parasites in initiation and exacerbation of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a prolonged and disabling functional gastrointestinal disorder with the incidence rate of 18% in the world. IBS could seriously affect lifetime of patients and cause high economic burden on the community. The pathophysiology of the IBS is hardly understood, whereas several possible mechanisms, such as visceral hypersensitivity, irregular gut motility, abnormal brain-gut relations, and the role of infectious agents, are implicated in initiation and development of this syndrome. Different studies demonstrated an alteration in B-lymphocytes, mast cells (MC), T-lymphocytes, and cytokine concentrations in intestinal mucosa or systemic circulation that are likely to contribute to the formation of the IBS. Therefore, IBS could be developed in those with genetic predisposition. Infections' role in initiation and exacerbation of IBS has been investigated by quite several clinical studies; moreover, the possible role of some pathogens in development and exacerbation of this disease has been described. It appears that the main obligatory pathogens correspond with the IBS disease, Clostridium difficile, Escherichia coli, Mycobacterium avium subspecies paratuberculosis, Campylobacter concisus, Campylobacter jejuni, Chlamydia trachomatis, Helicobacter pylori, Pseudomonas aeruginosa, Salmonella spp, Shigella spp, and viruses, particularly noroviruses. A number of pathogenic parasites (Blastocystis, Dientamoeba fragilis, and Giardia lamblia) may also be involved in the progression and exacerbation of the disease. Based on the current knowledge, the current study concludes that the most common bacterial, viral, and parasitic pathogens may be involved in the development and progression of IBS.

Clonality, virulence and antimicrobial resistance of enteroaggregative Escherichia coli from Mirzapur, Bangladesh

Purpose

This study investigates the virulence and antimicrobial resistance in association with common clonal complexes (CCs) of enteroaggregative Escherichia coli (EAEC) isolated from Bangladesh. The aim was to determine whether specific CCs were more likely to be associated with putative virulence genes and/or antimicrobial resistance.

Methodology

The presence of 15 virulence genes (by PCR) and susceptibility to 18 antibiotics were determined for 151 EAEC isolated from cases and controls during an intestinal infectious disease study carried out between 2007–2011 in the rural setting of Mirzapur, Bangladesh (Kotloff KL, Blackwelder WC, Nasrin D, Nataro JP, Farag TH et al.Clin Infect Dis 2012;55:S232–S245). These data were then analysed in the context of previously determined serotypes and clonal complexes defined by multi-locus sequence typing.

Results

Overall there was no association between the presence of virulence or antimicrobial resistance genes in isolates of EAEC from cases versus controls. However, when stratified by clonal complex (CC) one CC associated with cases harboured more virulence factors (CC40) and one CC harboured more resistance genes (CC38) than the average. There was no direct link between the virulence gene content and antibiotic resistance. Strains within a single CC had variable virulence and resistance gene content indicating independent and multiple gene acquisitions over time.

Conclusion

In Bangladesh, there are multiple clonal complexes of EAEC harbouring a variety of virulence and resistance genes. The emergence of two of the most successful clones appeared to be linked to either increased virulence (CC40) or antimicrobial resistance (CC38), but increased resistance and virulence were not found in the same clonal complexes.

Characterisation of Commensal Escherichia coli Isolated from Apparently Healthy Cattle and Their Attendants in Tanzania

While pathogenic types of Escherichia coli are well characterized, relatively little is known about the commensal E. coli flora. In the current study, antimicrobial resistance in commensal E. coli and distribution of ERIC-PCR genotypes among isolates of such bacteria from cattle and cattle attendants on cattle farms in Tanzania were investigated. Seventeen E. coli genomes representing different ERIC-PCR types of commensal E. coli were sequenced in order to determine their possible importance as a reservoir for both antimicrobial resistance genes and virulence factors. Both human and cattle isolates were highly resistant to tetracycline (40.8% and 33.1%), sulphamethazole-trimethoprim (49.0% and 8.8%) and ampicillin (44.9% and 21.3%). However, higher proportion of resistant E. coli and higher frequency of resistance to more than two antimicrobials was found in isolates from cattle attendants than isolates from cattle. Sixteen out of 66 ERIC-PCR genotypes were shared between the two hosts, and among these ones, seven types contained isolates from cattle and cattle attendants from the same farm, suggesting transfer of strains between hosts. Genome-wide analysis showed that the majority of the sequenced cattle isolates were assigned to phylogroups B1, while human isolates represented phylogroups A, C, D and E. In general, in silico resistome and virulence factor identification did not reveal differences between hosts or phylogroups, except for lpfA and iss found to be cattle and B1 phylogroup specific. The most frequent plasmids replicon genes found in strains from both hosts were of IncF type, which are commonly associated with carriage of antimicrobial and virulence genes. Commensal E. coli from cattle and attendants were found to share same genotypes and to carry antimicrobial resistance and virulence genes associated with both intra and extraintestinal E. coli pathotypes.

[Traveller's diarrhoea]

Traveller's diarrhoea (TD) is acquired primarily through ingestion of food and drinks contaminated with pathogens that cause diarrhoea. They can be bacteria, protozoa, helminths, and viruses. Globally, the most common causes of TD are two pathotypes of Escherichia coli (enterotoxigenic and enteroaggregative) and Campylobacter, although there are significant variations by geographic area visited. Most TD occurs in individuals traveling to low-middle income countries. The type of travel, length of stay, traveller's age, and the presence of certain underlying conditions are important risk factors to consider for the acquisition of TD. While TD is usually a mild and self-limiting disease, half of travellers with TD experience some limitation of activities during their trip, while up to 10% will experience persistent diarrhoea or other complications. The purpose of this article is to provide an updated microbiological, epidemiological, and clinical profile of traveller's diarrhoea, including known risk factors, as well as to make recommendations on the prevention and treatment of TD.

Fecal contamination of drinking water in Kericho District, Western Kenya: role of source and household water handling and hygiene practices

Inadequate protection of water sources, and poor household hygienic and handling practices have exacerbated fecal water contamination in Kenya. This study evaluated the rate and correlates of thermotolerant coliform (TTC) household water contamination in Kericho District, Western Kenya. Culture and multiplex polymerase chain reaction (PCR) techniques were used to characterize TTCs. The disk diffusion method was used for antibiotic susceptibility profiling of pathogenic Escherichia coli. Out of the 103 households surveyed, 48 (46.6%) had TTC contaminated drinking water (TTC levels of >10 cfu/100 mL). Five of these households were contaminated with pathogenic E. coli, including 40% enteroaggregative E. coli, 40% enterotoxigenic E. coli, and 20% enteropathogenic E. coli. All these pathogenic E. coli strains were multidrug resistant to sulfamethoxazole/trimethoprim, ampicillin, tetracycline and ampicillin/sulbactam. Rural household locality, drinking water hand contact, water storage container cleaning practice, hand washing before water withdrawal, water source total coliforms <10 cfu/100 mL, temperature, and free chlorine levels were associated with TTC contamination of household drinking water. Significant proportions of household drinking water in Kericho District are contaminated with TTCs including with pathogenic multidrug-resistant E. coli. Source and household hygiene and practices contribute significantly to drinking water contamination.

Combination vaccines against diarrheal diseases

Diarrheal diseases remain a leading cause of global childhood mortality and morbidity. Several recent epidemiological studies highlight the rate of diarrheal diseases in different parts of the world and draw attention to the impact on childhood growth and survival. Despite the well-documented global burden of diarrheal diseases, currently there are no combination diarrheal vaccines, only licensed vaccines for rotavirus and cholera, and Salmonella typhi-based vaccines for typhoid fever. The recognition of the impact of diarrheal episodes on infant growth, as seen in resource-poor countries, has spurred action from governmental and non-governmental agencies to accelerate research toward affordable and effective vaccines against diarrheal diseases. Both travelers and children in endemic countries will benefit from a combination diarrheal vaccine, but it can be argued that the greater proportion of any positive impact will be on the public health status of the latter. The history of combination pediatric vaccines indicate that monovalent or single disease vaccines are typically licensed first prior to formulation in a combination vaccine, and that the combinations themselves undergo periodic revision in response to need for improvement in safety or potential for wider coverage of important pediatric pathogens. Nevertheless combination pediatric vaccines have proven to be an effective tool in limiting or eradicating communicable childhood diseases worldwide. The landscape of diarrheal vaccine candidates indicates that there now several in active development that offer options for potential testing of combinations to combat those bacterial and viral pathogens responsible for the heaviest disease burden—rotavirus, ETEC, Shigella, Campylobacter, V. cholera and Salmonella.

Virulence factors and mechanisms of antimicrobial resistance in Shigella strains from periurban areas of Lima (Peru)

The study was aimed to describe the serotype, mechanisms of antimicrobial resistance, and virulence determinants in Shigella spp. isolated from Peruvian children. Eighty three Shigella spp. were serogrouped and serotyped being established the antibiotic susceptibility. The presence of 12 virulence factors (VF) and integrase 1 and 2, along with commonly found antibiotic resistance genes was established by PCR. S. flexneri was the most relevant serogroup (55 isolates, 66%), with serotype 2a most frequently detected (27 of 55, 49%), followed by S. boydii and S. sonnei at 12 isolates each (14%) and S. dysenteriae (four isolates, 5%). Fifty isolates (60%) were multi-drug resistant (MDR) including 100% of S. sonnei and 64% of S. flexneri. Resistance levels were high to trimethoprim-sulfamethoxazole (86%), tetracycline (74%), ampicillin (67%), and chloramphenicol (65%). Six isolates showed decreased azithromycin susceptibility. No isolate was resistant to nalidixic acid, ciprofloxacin, nitrofurantoin, or ceftriaxone. The most frequent resistance genes were sul2 (95%), tet(B) (92%), cat (80%), dfrA1 (47%), blaOXA-1like (40%), with intl1 and intl2 detected in 51 and 52% of the isolates, respectively. Thirty-one different VF profiles were observed, being the ipaH (100%), sen (77%), virA and icsA (75%) genes the most frequently found. Differences in the prevalence of VF were observed between species with S. flexneri isolates, particularly serotype 2a, possessing high numbers of VF. In conclusion, this study highlights the high heterogeneity of Shigella VF and resistance genes, and prevalence of MDR organisms within this geographic region.

Occurrence of genes encoding enterotoxins in uropathogenic Escherichia coli isolates

To determine the presence of some toxins of diarrheagenic Escherichia coli (DEC) in uropathogenic E. coli (UPEC), 138 urinary tract infection (UTI)-causing UPECs were analyzed. The astA , set , sen and cdtB genes were detected in 13 (9.4%), 2 (1.3%), 13 (9.4%) and 0 (0%) of UPEC isolates respectively. The results show that some genes encoding toxins can be transferred from DEC pathotypes to UPECs therefore these isolates can transform into potential diarrhea-causing agents.

Adherence and virulence genes of Escherichia coli from children diarrhoea in the Brazilian Amazon

The bacterial pathogen most commonly associated with endemic forms of childhood diarrhoea is Escherichia coli . Studies of epidemiological characteristics of HEp-2 cell-adherent E. coli in diarrhoeal disease are required, particularly in developing countries. The aim of this study was evaluate the presence and significance of adherent Escherichia coli from diarrhoeal disease in children. The prevalence of LA, AA, and DA adherence patterns were determined in HEp-2 cells, the presence of virulence genes and the presence of the O serogroups in samples obtained from 470 children with acute diarrhoea and 407 controls in Porto Velho, Rondônia, Brazil. E. coli isolates were identified by PCR specific for groups of adherent E. coli . Out of 1,156 isolates obtained, 128 (11.0%) were positive for eae genes corresponding to EPEC, however only 38 (29.6%) of these amplified bfpA gene . EAEC were isolated from 164 (14.1%) samples; of those 41(25%), 32 (19%) and 16 (9.7%) amplified eagg , aggA or aafA genes, respectively and aggA was significantly associated with diarrhoea ( P = 0.00006). DAEC identified by their adhesion pattern and there were few isolates. In conclusion, EAEC was the main cause of diarrhoea in children, especially when the aggA gene was present, followed by EPEC and with a negligible presence of DAEC.

Zinc deficiency alters host response and pathogen virulence in a mouse model of enteroaggregative Escherichia coli-induced diarrhea

Enteroaggregative Escherichia coli (EAEC) is increasingly recognized as a major cause of diarrheal disease globally. In the current study, we investigated the impact of zinc deficiency on the host and pathogenesis of EAEC. Several outcomes of EAEC infection were investigated including weight loss, EAEC shedding and tissue burden, leukocyte recruitment, intestinal cytokine expression, and virulence expression of the pathogen in vivo. Mice fed a protein source defined zinc deficient diet (dZD) had an 80% reduction of serum zinc and a 50% reduction of zinc in luminal contents of the bowel compared to mice fed a protein source defined control diet (dC). When challenged with EAEC, dZD mice had significantly greater weight loss, stool shedding, mucus production, and, most notably, diarrhea compared to dC mice. Zinc deficient mice had reduced infiltration of leukocytes into the ileum in response to infection suggesting an impaired immune response. Interestingly, expression of several EAEC virulence factors were increased in luminal contents of dZD mice. These data show a dual effect of dietary zinc in benefitting the host while impairing virulence of the pathogen. The study demonstrates the critical importance of zinc and may help elucidate the benefits of zinc supplementation in cases of childhood diarrhea and malnutrition.

Two novel EHEC/EAEC hybrid strains isolated from human infections

The so far highest number of life-threatening hemolytic uremic syndrome was associated with a food-borne outbreak in 2011 in Germany which was caused by an enterohemorrhagic Escherichia coli (EHEC) of the rare serotype O104:H4. Most importantly, the outbreak strain harbored genes characteristic of both EHEC and enteroaggregative E. coli (EAEC). Such strains have been described seldom but due to the combination of virulence genes show a high pathogenicity potential. To evaluate the importance of EHEC/EAEC hybrid strains in human disease, we analyzed the EHEC strain collection of the German National Reference Centre for Salmonella and other Bacterial Enteric Pathogens (NRC). After exclusion of O104:H4 EHEC/EAEC strains, out of about 2400 EHEC strains sent to NRC between 2008 and 2012, two strains exhibited both EHEC and EAEC marker genes, specifically were stx2 and aatA positive. Like the 2011 outbreak strain, one of the novel EHEC/EAEC harbored the Shiga toxin gene type stx2a. The strain was isolated from a patient with bloody diarrhea in 2010, was serotyped as O59:H⁻, belonged to MLST ST1136, and exhibited genes for type IV aggregative adherence fimbriae (AAF). The second strain was isolated from a patient with diarrhea in 2012, harbored stx2b, was typed as Orough:H⁻, and belonged to MLST ST26. Although the strain conferred the aggregative adherence phenotype, no known AAF genes corresponding to fimbrial types I to V were detected. In summary, EHEC/EAEC hybrid strains are currently rarely isolated from human disease cases in Germany and two novel EHEC/EAEC of rare serovars/MLST sequence types were characterized.

Heteropathogenic virulence and phylogeny reveal phased pathogenic metamorphosis in Escherichia coli O2:H6

Extraintestinal pathogenic and intestinal pathogenic (diarrheagenic) Escherichia coli differ phylogenetically and by virulence profiles. Classic theory teaches simple linear descent in this species, where non-pathogens acquire virulence traits and emerge as pathogens. However, diarrheagenic Shiga toxin-producing E. coli (STEC) O2:H6 not only possess and express virulence factors associated with diarrheagenic and uropathogenic E. coli but also cause diarrhea and urinary tract infections. These organisms are phylogenetically positioned between members of an intestinal pathogenic group (STEC) and extraintestinal pathogenic E. coli. STEC O2:H6 is, therefore, a 'heteropathogen,' and the first such hybrid virulent E. coli identified. The phylogeny of these E. coli and the repertoire of virulence traits they possess compel consideration of an alternate view of pathogen emergence, whereby one pathogroup of E. coli undergoes phased metamorphosis into another. By understanding the evolutionary mechanisms of bacterial pathogens, rational strategies for counteracting their detrimental effects on humans can be developed.

Characterization of Escherichia coli isolates from hospital inpatients or outpatients with urinary tract infection

Uropathogenic Escherichia coli (UPEC) is the most common cause of community- and hospital-acquired urinary tract infections (UTIs). Isolates from uncomplicated community-acquired UTIs express a variety of virulence traits that promote the efficient colonization of the urinary tract. In contrast, nosocomial UTIs can be caused by E. coli strains that differ in their virulence traits from the community-acquired UTI isolates. UPEC virulence markers are used to distinguish these facultative extraintestinal pathogens, which belong to the intestinal flora of many healthy individuals, from intestinal pathogenic E. coli (IPEC). IPEC is a diarrheagenic pathogen with a characteristic virulence gene set that is absent in UPEC. Here, we characterized 265 isolates from patients with UTIs during inpatient or outpatient treatment at a hospital regarding their phylogenies and IPEC or UPEC virulence traits. Interestingly, 28 of these isolates (10.6%) carried typical IPEC virulence genes that are characteristic of enteroaggregative E. coli (EAEC), Shiga toxin-producing E. coli (STEC), and atypical enteropathogenic E. coli (aEPEC), although IPEC is not considered a uropathogen. Twenty-three isolates harbored the astA gene coding for the EAEC heat-stable enterotoxin 1 (EAST1), and most of them carried virulence genes that are characteristic of UPEC and/or EAEC. Our results indicate that UPEC isolates from hospital patients differ from archetypal community-acquired isolates from uncomplicated UTIs by their spectrum of virulence traits. They represent a diverse group, including EAEC, as well as other IPEC pathotypes, which in addition contain typical UPEC virulence genes. The combination of typical extraintestinal pathogenic E. coli (ExPEC) and IPEC virulence determinants in some isolates demonstrates the marked genome plasticity of E. coli and calls for a reevaluation of the strict pathotype classification of EAEC.

Presence of multi-drug resistant pathogenic Escherichia coli in the San Pedro River located in the State of Aguascalientes, Mexico

Contamination of surface waters in developing countries is a great concern. Treated and untreated wastewaters have been discharged into rivers and streams, leading to possible waterborne infection outbreaks and may represent a significant dissemination mechanism of antibiotic resistance genes. In this study, the water quality of San Pedro River, the main river and pluvial collector of the Aguascalientes State, Mexico was assessed. Thirty sample locations were tested throughout the River. The main physicochemical parameters of water were evaluated. Results showed high levels of fecal pollution as well as inorganic and organic matter abundant enough to support the heterotrophic growth of microorganisms. These results indicate poor water quality in samples from different locations. One hundred and fifty Escherichia coli were collected and screened by PCR for several virulence genes. Isolates were classified as either pathogenic (n = 91) or commensal (n = 59). The disc diffusion method was used to determine antimicrobial susceptibility to 13 antibiotics. Fifty-two percent of the isolates were resistant to at least one antimicrobial agent and 30.6% were multi-resistant. Eighteen E. coli strains were quinolone resistant of which 16 were multi-resistant. Plasmid-mediated quinolone resistance (PMQR) genes were detected in 12 isolates. Mutations at the Ser-83→Leu and/or Asp-87→Asn in the gyrA gene were detected as well as mutations at the Ser-80→Ile in parC. An E. coli microarray (Maxivirulence V 3.1) was used to characterize the virulence and antimicrobial resistance genes profiles of the fluoroquinolone-resistant isolates. Antimicrobial resistance genes such as bla TEM, sulI, sulII, dhfrIX, aph3 (strA), and tet (B) as well as integrons were found in fluoroquinolone (FQ) resistance E. coli strains. The presence of potential pathogenic E. coli and antibiotic resistance in San Pedro River such as FQ resistant E. coli could pose a potential threat to human and animal health.

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.

Characterization of a novel EAST-negative enteropathogenic E. coli strain implicated in a food-borne outbreak of diarrhoea in adults

Enteropathogenic Escherichia coli (EPEC) is usually associated with outbreaks and sporadic cases of severe infantile diarrhoea in the developing world, and less commonly with sporadic cases in developed countries. Very little evidence indicates that EPEC is a food-borne pathogen for adults. In a previous study, two groups of adult travellers became ill, and eae(+) E. coli of serogroup O111 was isolated from affected individuals and epidemiologically linked to food consumption. Here the strain responsible was further investigated and characterized as an unusual atypical EPEC. PCR analysis of the designated type isolate showed the presence of the rorf1 and espB genes of the LEE pathogenicity island, which was inserted at the chromosomal selC locus. The isolate was negative for the enteroaggregative E. coli EAST-1 toxin present in other strains of EPEC associated with food-borne outbreaks. The strain adhered sparsely to HEp-2 cell monolayers in a diffuse manner, but fluorescent actin staining demonstrated that it was capable of inducing polymerization of actin at the sites of bacterial attachment. Strain P2583 is the first EAST-negative EPEC to be confirmed as a cause of outbreaks of infection in adults following the consumption of contaminated food or water.

Characterization of the AggR regulon in enteroaggregative Escherichia coli

AggR is a transcriptional regulator of enteroaggregative Escherichia coli (EAEC) and has been proposed as the defining factor for typical EAEC strains. Expression of multiple putative virulence factors, including the aggregative adherence fimbriae (AAF), dispersin, the dispersin translocator Aat, and the Aai type VI secretion system, have been found to be regulated by AggR. Here, we confirm the existence of at least 44 AggR-regulated genes using DNA microarray and real-time quantitative reverse transcription-PCR (qRT-PCR); these genes include chromosomal and plasmid-borne loci and 19 previously unsuspected genes. Two previously uncharacterized virulence plasmid-encoded open reading frames (ORFs) (designated ORF3 and ORF4) exhibit significant identity with isoprenoid biosynthesis genes of Bacteria and Archaea. The predicted ORF4 product is closely related to isopentenyl isomerase (IDI) enzymes, whereas the predicted product of the adjacent ORF3 exhibits an aspartate-rich region that is common among trans-isoprenyl phosphate synthases. We show that mutations in these ORFs confer changes in bacterial surface properties. AggR coordinately controls expression of a large number of EAEC genes.

Serogroups and virulence genes of Escherichia coli isolated from psittacine birds

Escherichia coli isolates from 24 sick psittacine birds were serogrouped and investigated for the presence of genes encoding the following virulence factors: attaching and effacing (eae), enteropathogenic E. coli EAF plasmid (EAF), pili associated with pyelonephritis (pap), S fimbriae (sfa), afimbrial adhesin (afa), capsule K1 (neu), curli (crl, csgA), temperature-sensitive hemagglutinin (tsh), enteroaggregative heat-stable enterotoxin-1 (astA), heat-stable enterotoxin -1 heat labile (LT) and heat stable (STa and STb) enterotoxins, Shiga-like toxins (stx1 and stx2), cytotoxic necrotizing factor 1 (cnf1), haemolysin (hly), aerobactin production (iuc) and serum resistance (iss). The results showed that the isolates belonged to 12 serogroups: O7; O15; O21; O23; O54; O64; O76; O84; O88; O128; O152 and O166. The virulence genes found were: crl in all isolates, pap in 10 isolates, iss in seven isolates, csgA in five isolates, iuc and tsh in three isolates and eae in two isolates. The combination of virulence genes revealed 11 different genotypic patterns. All strains were negative for genes encoding for EAF, EAEC, K1, sfa, afa, hly, cnf, LT, STa, STb, stx1 and stx2. Our findings showed that some E. coli isolated from psittacine birds present the same virulence factors as avian pathogenic E. coli (APEC), uropathogenic E. coli (UPEC) and Enteropathogenic E. coli (EPEC) pathotypes.

Characterization of enteroaggregative Escherichia coli (EAEC) clinical isolates and their antibiotic resistance pattern

OBJECTIVES

Enteroaggregative Escherichia coli (EAEC) strains are an emerging type of diarrheagenic E. coli. The aim of this study was to investigate the frequency of EAEC in children with diarrhea by polymerase chain reaction (PCR) method targeting the pCVD432 gene. The presence of virulence genes including aggR, aggA, aafA, aap, and astA was also investigated by PCR, for the differentiation of typical and atypical EAEC strains. We also sought to determine the antibiotic resistance pattern of the isolated strains.

METHODS

Stool samples were collected from 140 children with diarrhea at Besat Hospital, Hamadan, Iran, from July 2007 to May 2008. The specimens were cultured for E. coli, which was identified using standard methods. E. coli strains were screened for EAEC by PCR and HeLa cell line adherence methods. For each sample, five single colonies (700 E. coli strains) from original MacConkey plates were examined for pCVD432, aggR, aggA, aafA, aap, and astA genes using PCR. The EAEC adherence patterns were examined by HeLa cell adherence method. Antimicrobial susceptibility testing was performed as the Clinical and Laboratory Standards Institute (CLSI) guidelines.

RESULTS

Overall, 15 (10.7%) EAEC strains were identified in 140 diarrhea cases by PCR. Out of these isolates, EAEC were detected in 13 (86.7%) by the HeLa cell assay. The aggR regulon was present in 11 (73.3%) strains. Several different combinations of the virulence markers were found among the EAEC isolates. The most prevalent (20%) combination was aggR-aap-astA. The EAEC isolates exhibited resistance to ampicillin (100%), erythromycin (100%), cephalothin (78.6%), co-trimoxazole (71.4%), tetracycline (64.3%), and nalidixic acid (57.1%) and reduced resistance to ciprofloxacin (42.9%) and norfloxacin (7.1%).

CONCLUSIONS

EAEC is a diarrheal pathogen of emerging importance. Correlation between pCVD432 PCR and the HeLa cell line assay was confirmed in children with diarrhea. In comparison to the assay for aggregative adherence, the EAEC PCR has been found to be simple and specific in many epidemiological studies. The typical EAEC (73.3%) strains (with pCVD432 and aggR genes) identified in this study were heterogeneous with respect to virulence genes. This study also showed that EAEC isolates were highly resistant to tetracycline, co-trimoxazole, and ampicillin, which are the most commonly used antibiotics in our area.

Prevalence of enterotoxins among Escherichia coli isolates causing bacteraemia

The most frequent cause of bacteraemia among Gram-negative bacteria is Escherichia coli. Analysis of the genes encoding the Shigella enterotoxin 1 (ShET-1), ShET-2, enteroaggregative heat stable toxin 1 (EAST-1) toxins and AggR factor in E. coli strains causing bacteraemia revealed that set1 genes were presented significantly more frequently among quinolone-susceptible strains (P<0.0001), in phylogenetic group B2 (P=0.0004) and in biofilm strains (P=0.02). In contrast, sen genes were significantly more frequent among nalidixic acid-resistant isolates (15% vs. 6%, P=0.046) and in phylogenetic group B1 (P=0.0001). This is the first study in which ShET1, ShET2 and EAST-1 have been found in E. coli collected from blood.

A new multiplex PCR for differential identification ofShigella flexneriandShigella sonneiand detection ofShigellavirulence determinants

Most of the multiplex PCR (mPCR) used to identifyShigellado not discriminate betweenShigellaspecies or serotypes. We designed a mPCR to differentiate betweenS. flexneriandS. sonneistrains based on the detection of markers associated with theshepathogenicity island described inShigella. In addition, specific primers were included to detect theShigellavirulence determinants ShET-1 and ShET-2 enterotoxin genes. The analysis of 304Shigellastrains from Chile and 79Shigellastrains from other geographic locations indicated that the mPCR described here detected allShigellaspecies and specifically differentiatedS. flexneriandS. sonnei. The technique was sensitive, reproducible, specific and simple to perform, providing a new tool with the potential to be employed for epidemiological and diagnostic purposes.

Prevalence of the set-1B and astA genes encoding enterotoxins in uropathogenic Escherichia coli clinical isolates

One hundred seventy human uropathogenic Escherichia coli (UPEC) clinical isolates were compared with 35 E. coli strains isolated from feces of a control group to determine the presence of the set1, sen and astA genes encoding the ShET-1, ShET-2, and EAST toxins, respectively. Overall, 27 (16%), 8 (8%) and 0 UPEC isolates presented the set1B, the astA, and the sen genes, respectively. This is the first time the set gene has been found in UPEC clinical isolates.

Pathogenic Escherichia coli and food handlers in luxury hotels in Nairobi, Kenya

BACKGROUND

The epidemiology and virulence properties of pathogenic Escherichia coli among food handlers in tourist destination hotels in Kenya are largely uncharacterized.

METHOD

This cross-sectional study among consenting 885 food handlers working in nine luxurious tourist hotels in Nairobi, Kenya determined the epidemiology, virulence properties, antibiotics susceptibility profiles and conjugation abilities of pathogenic Escherichia coli.

RESULT

Pathogenic Escherichia coli was detected among 39 (4.4%) subjects, including 1.8% enteroaggregative Escherichia coli (EAEC) harboring aggR genes, 1.2% enterotoxigenic Escherichia coli (ETEC) expressing both LT and STp toxins, 1.1% enteropathogenic Escherichia coli (EPEC) and 0.2% Shiga-like Escherichia coli (EHEC) both harboring eaeA and stx2 genes respectively. All the pathotypes had increased surface hydrophobicity. Using multivariate analyses, food handlers with loose stools were more likely to be infected with pathogenic Escherichia coli. Majority 53.8% of the pathotypes were resistant to tetracycline with 40.2% being multi-drug resistant. About 85.7% pathotypes trans-conjugated with Escherichia coli K12 F(-) NA(r) LA.

CONCLUSION

The carriage of multi-drug resistant, toxin expressing pathogenic Escherichia coli by this population is of public health concern because exposure to low doses can result in infection. Screening food handlers and implementing public awareness programs is recommended as an intervention to control transmission of enteric pathogens.

Pet secretion, internalization and induction of cell death during infection of epithelial cells by enteroaggregative Escherichia coli

In an in vitro model using HEp-2 cells treated with purified plasmid-encoded toxin (Pet), we have identified morphological changes characterized by cell rounding and detachment after toxin internalization; these changes progress to cell death. However, these effects have not yet been shown to occur during the infection of epithelial cells by enteroaggregative Escherichia coli (EAEC). Here, we show that the secretion of Pet by EAEC is regulated at the transcriptional level, since secretion was inhibited in eukaryotic cell culture medium, although Pet was efficiently secreted in the same medium supplemented with tryptone. Inefficient secretion of Pet by EAEC in DMEM prevented cell detachment, whereas efficient Pet secretion in DMEM/tryptone increased cell detachment in a HEp-2 cell adherence assay. Interestingly, Pet toxin was efficiently delivered to epithelial cells, since it was internalized into epithelial cells infected with EAEC at similar concentrations to those obtained by using 37 microg ml(-1) purified Pet protein. Additionally, Pet was not internalized when the epithelial cells were infected with a pet clone, HB101(pCEFN1), unlike the wild-type strain, which has a high adherence capability. There is a correlation between Pet secretion by EAEC, the internalization of Pet into epithelial cells, cell detachment and cell death in EAEC-infected cells. The ratio between live and dead cells decreased in cells treated with wild-type EAEC in comparison with cells treated with an isogenic mutant in the pet gene, whereas the effects were restored by complementing the mutant with the pet gene. All these data indicate that Pet is an important virulence factor in the pathogenesis of EAEC infection.

The prevalence and virulence characteristics of enteroaggregative Escherichia coli at an urgent-care clinic in the USA: a case-control study

This case-control study examined the prevalence of enteroaggregative Escherichia coli (EAEC), its genes and elicited inflammatory response, and the stool characteristics of adult patients with and without acute diarrhoeal illness presenting to an urgent-care clinic in the USA. A total of 1004 individual stool specimens (253 from patients with acute diarrhoeal illness and 751 from patients without diarrhoeal illness) were collected between 1 June 2003 and 30 June 2008. EAEC was identified as the sole cause of acute diarrhoeal illness in 6 % (n=15) of patients and in 2 % (n=15) without diarrhoeal illness. Control patients (n=15) were similar to case patients (n=15) for age, gender and co-morbidities. The EAEC genes aggR, aap, aat, astA and/or set1A were identified more frequently in case patients compared with control patients (P <0.05). aggR-positive EAEC elicited higher levels of interleukin (IL)-1ra, IL-6, IL-8 and tumour necrosis factor-alpha compared with aggR-negative EAEC during co-incubation with HCT-8 cells. Patients with EAEC diarrhoea and isolates with the genes aggR, aap, aatA, astA or set1A had stools characterized by gross mucus and the presence of faecal leukocytes (P <0.05). These results indicate that EAEC is a potential cause of acute diarrhoeal illness affecting patients presenting to an acute-care clinic in the USA and suggest that aggR, aap, aatA, astA and set1A may be markers for virulence.

New adhesin of enteroaggregative Escherichia coli related to the Afa/Dr/AAF family

Enteroaggregative Escherichia coli (EAEC) is an important cause of diarrhea worldwide. We analyzed 17 Danish EAEC strains, isolated in the course of a case control study, for phenotypic and genotypic properties. The strains belonged to at least 14 different serotypes. Using PCR to investigate the prevalence of various putative virulence genes, we found that all but two strains were typical EAEC, as they harbored all or part of the previously described AggR regulon. The majority of the strains harbored genes encoding aggregative adherence fimbriae (AAF). The most common was AAF/I, found in nine strains; eight strains carried no known AAF-related genes. We utilized TnphoA mutagenesis to localize the aggregative adherence (AA) adhesin from one typical EAEC strain, C1010-00, which lacked a known AAF. We identified a TnphoA insertion in a hypothetical Dr-related pilin deposited in GenBank as HdaA. Four additional Danish strains harbored HdaA, and all but one displayed AA to HEp-2 cells. By using PCR primers derived from the pilins and ushers from the three AAF and Hda, we found that 16 of 17 strains exhibited evidence of one of these factors; importantly, the one negative strain also lacked the aggR gene. Cloning of the complete Hda gene cluster and expression in E. coli DH5alpha resulted in AA and complementation of the C1010-00 nonadherent mutant. Four related adhesins have now been found to confer AA in typical EAEC strains; our data suggest that, together, these variants may account for AA in the large majority of strains.

Type 3 fimbriae, encoded by the conjugative plasmid pOLA52, enhance biofilm formation and transfer frequencies in Enterobacteriaceae strains

The conjugative plasmid pOLA52, which confers resistance to olaquindox and other antimicrobial agents through a multidrug efflux pump, was investigated for its ability to promote biofilm formation in Escherichia coli. Screening of a transposon-mutagenized pOLA52 clone library revealed several biofilm-deficient mutants, which all mapped within a putative operon with high homology to the mrkABCDF operon of Klebsiella pneumoniae, where these genes are responsible for type 3 fimbriae expression, attachment to surfaces and biofilm formation. Biofilm formation in microtitre plates and in urinary catheters of clones containing pOLA52 with a disrupted putative mrk operon was reduced by more than 100-fold and 2-fold, respectively, compared to mutants with an intact mrk operon. The conjugative transfer rate of pOLA52 was also significantly lower when the mrk operon was disrupted. Through reverse transcriptase analysis, it was demonstrated that the genes contained in the putative mrk operon were linked and likely to be expressed as a single operon. Immunoblotting with type 3 fimbriae (MrkA)-specific antibodies further verified expression of type 3 fimbriae. When transferred to other, potentially pathogenic, members of the family Enterobacteriaceae, including Klebsiella pneumoniae, Salmonella Typhimurium, Kluyvera sp. and Enterobacter aerogenes, pOLA52 facilitated increased biofilm formation. pOLA52 is believed to represent the first example of a conjugative plasmid encoding type 3 fimbriae, resulting in enhanced conjugation frequencies and biofilm formation of the plasmid-harbouring strain.

Association of putative pathogenicity genes with adherence characteristics and fimbrial genotypes in typical enteroaggregative Escherichia coli from patients with and without diarrhoea in the United Kingdom

The aim of this study was to compare genotypic characteristics seen in typical EAggEC isolated during a study of intestinal infectious disease from cases and controls, and to identify which genes, or combinations of genes, were most associated with diarrhoeal disease. We also investigated the association of genotype with certain characteristics, such as presence of fimbrial genes and adherence to Hep-2 cells. The aafC gene, encoding the usher for AAFII, was the only gene significantly associated with patients with diarrhoea (P < 0.005), and the aggC gene, which encodes the usher for AAFI, was the only gene significantly associated with the healthy control group (P < 0.002). Putative virulence genes significantly associated with aggregative adherence included aafC, aggR, pet, pic and astA. The shf, pet and astA genes were all more likely to be associated with type II fimbriae than with type I. We conclude that in addition to presence and absence of certain genes, studies of EAggEC pathogenicity should investigate the combinations and associations of putative virulence factors.

CTX-M-15-producing multidrug-resistant enteroaggregative Escherichia coli in the United Arab Emirates

Extended-spectrum beta-lactamase (ESBL) production was demonstrated in five independent, multidrug-resistant isolates of enteroaggregative Escherichia coli (EAEC) from the United Arab Emirates, representing 11.3% of the EAEC isolates recovered during 1 year. All five isolates carried the bla(CTX-M-15) and the bla(TEM-1) genes, the former positioned 48 bp downstream of an ISecp1 element. In two isolates, the bla(CTX-M-15 )and bla(TEM-1) genes were located on a 95-kb plasmid. This is the first detailed description and characterisation of ESBL production in enteroaggregative E. coli and also the first report of CTX-M-producing organisms encountered on the Arabian Peninsula.

Association of enteroaggregative Escherichia coli with irritable bowel syndrome

Increased numbers of faecal Enterobacteriaceae are observed among patients with irritable bowel syndrome. Escherichia coli strains are present in the lower intestine of humans, and may include several potentially pathogenic adhesive pathotypes. The aim of this study was to determine whether there were differences between the adhesive pathotypes of E. coli strains recovered from stool specimens of patients with irritable bowel syndrome and those recovered from healthy controls. The ability of E. coli isolates to adhere to cultured epithelial cells was assessed in an in-vitro adherence assay with HEp-2 cells. Enteroaggregative E. coli (EAEC) strains were isolated significantly more frequently (p <0.00001) from patients with irritable bowel syndrome (81.8%) than from healthy controls (32.3%). However, despite this association, the precise role of the EAEC pathotype in irritable bowel syndrome remains to be determined.

Autotransporter-encoding sequences are phylogenetically distributed among Escherichia coli clinical isolates and reference strains

Autotransporters are secreted bacterial proteins exhibiting diverse virulence functions. Various autotransporters have been identified among Escherichia coli associated with intestinal or extraintestinal infections; however, the specific distribution of autotransporter sequences among a diversity of E. coli strains has not been investigated. We have validated the use of a multiplex PCR assay to screen for the presence of autotransporter sequences. Herein, we determined the presence of 13 autotransporter sequences and five allelic variants of antigen 43 (Ag43) among 491 E. coli isolates from human urinary tract infections, diarrheagenic E. coli, and avian pathogenic E. coli (APEC) and E. coli reference strains belonging to the ECOR collection. Clinical isolates were also classified into established phylogenetic groups. The results indicated that Ag43 alleles were significantly associated with clinical isolates (93%) compared to commensal isolates (56%) and that agn43K12 was the most common and widely distributed allele. agn43 allelic variants were also phylogenetically distributed. Sequences encoding espC, espP, and sepA and agn43 alleles EDL933 and RS218 were significantly associated with diarrheagenic E. coli strains compared to other groups. tsh was highly associated with APEC strains, whereas sat was absent from APEC. vat, sat, and pic were associated with urinary tract isolates and were identified predominantly in isolates belonging to either group B2 or D of the phylogenetic groups based on the ECOR strain collection. Overall, the results indicate that specific autotransporter sequences are associated with the source and/or phylogenetic background of strains and suggest that, in some cases, autotransporter gene profiles may be useful for comparative analysis of E. coli strains from clinical, food, and environmental sources.

Comparative analysis of virulence genes, genetic diversity, and phylogeny of commensal and enterotoxigenic Escherichia coli isolates from weaned pigs

If the acquisition of virulence genes (VGs) for pathogenicity were not solely acquired through horizontal gene transfers of pathogenicity islands, transposons, and phages, then clonal clusters of enterotoxigenic Escherichia coli (ETEC) would contain few or even none of the VGs found in strains responsible for extraintestinal infections. To evaluate this possibility, 47 postweaning diarrhea (PWD) ETEC strains from different geographical origins and 158 commensal E. coli isolates from the gastrointestinal tracts of eight group-housed healthy pigs were screened for 36 extraintestinal and 18 enteric VGs using multiplex PCR assays. Of 36 extraintestinal VGs, only 8 were detected (fimH, traT, fyuA, hlyA, kpsMtII, k5, iha, and ompT) in the ETEC collection. Among these, hlyA (alpha-hemolysin) and iha (nonhemagglutinating adhesin) occurred significantly more frequently among the ETEC isolates than in the commensal isolates. Clustering analysis based on the VG profiles separated commensal and ETEC isolates and even differentiated serogroup O141 from O149. On the other hand, pulsed-field gel electrophoresis (PFGE) successfully clustered ETEC isolates according to both serotype and geographical origin. In contrast, the commensal isolates were heterogeneous with respect to both serotype and DNA fingerprint. This study has validated the use of VG profiling to examine pathogenic relationships between porcine ETEC isolates. The clonal relationships of these isolates can be further clarified by PFGE fingerprinting. The presence of extraintestinal VGs in porcine ETEC confirmed the hypothesis that individual virulence gene acquisitions can occur concurrently against a background of horizontal gene transfers of pathogenicity islands. Over time, this could enable specific clonotypes to respond to host selection pressure and to evolve into new strains with increased virulence.

Antibody response against plasmid-encoded toxin (Pet) and the protein involved in intestinal colonization (Pic) in children with diarrhea produced by enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) is an emerging cause of pediatric and adult travellers diarrhea. The mechanism by which EAEC induce diarrhea is not completely known. Two serine protease autotransporter proteins, named Pet and Pic have been identified in EAEC strains. Pet has enterotoxic and cytotoxic activities, while the role of Pic in pathogenesis may lie on its mucinolytic activity. Little is known about Pet and Pic biological activities in vivo. In this study the antibody responses against these autotransporter proteins in convalescent children is investigated. Fifteen (83%) children showed specific antibodies against Pet or Pic in their sera. IgG and IgM antibodies were the main isotype found. Specific antibodies against Pic, but not against Pet, were detected in sera from age-matched control group. These data show that specific anti-Pet and anti-Pic antibodies are produced during the course of a natural EAEC infection in children.

Heterogeneity among strains of diffusely adherent Escherichia coli isolated in Brazil

One hundred twelve diffusely adherent Escherichia coli strains isolated from children in a case control study were evaluated for virulence-associated characteristics, serotyping, antibiotic resistance, and plasmid profiles. Half of the strains hybridized with the probes for icuA (aerobactin) and fimH (type 1 pili); daaE (F1845 fimbriae), afa (afimbrial Dr adhesin), agg-3A (aggregative adhesion fimbria type III fimbriae), pap (P fimbriae), astA (EAST1 toxin), and shET1 (Shigella enterotoxin 1) sequences were present in <20% of the strains. The shET1 gene was noted most frequently in strains isolated from patients. A minority (7%) of the strains produced hemolysin or colicin or showed cytotoxic effects on Vero cells. Forty-five different serotypes were found. The majority (70%) of the strains presented multiple antibiotic resistance. Antibiotic resistance and diffuse adherence were located on the same conjugative plasmids. These results suggest that the transfer of these potential virulence markers could be important in the epidemiology of diffusely adherent E. coli.

Enteroaggregative Escherichia coli: An emerging pathogen in children

Enteroaggregative Escherichia coli (EAEC) is an emerging pathogen that causes enteric and food-borne infectious diseases. Children throughout the world appear to be susceptible to EAEC infection. EAEC pathogenesis involves the following three stages: 1) adherence to the intestinal mucosa; 2) increased production and deposition of a mucus biofilm; and 3) mucosal toxicity due to inflammation and cytokine release. The HEp-2 cell adherent assay allows identification of EAECs characteristic aggregative or "stacked brick" adherence pattern. Antimicrobial treatment of children who develop an EAEC infection should be individually based. All children with EAEC diarrhea should receive adequate oral fluid hydration. For children who have persistent diarrhea and severe dehydrating illness despite having received adequate oral rehydration, antimicrobials may be initiated. Azithromycin and rifaximin have been shown to shorten the course of EAEC diarrhea in adults and probably represent the recommended antimicrobials of choice for children with severe or persistent illness. The objective of this review is to increase awareness of this important emerging pathogen and to discuss the epidemiology, pathogenesis, and pathogen and host factors associated with EAEC infection in children.

A biologically active lectin of enteroaggregative Escherichia coli

The pathogenesis of enteroaggregative Escherichia coli, a major contributor to paediatric diarrhoea, is still not clearly understood. A complex carbohydrate specific lectin was identified from the culture supernatant of an enteroaggregative E. coli strain. The lectin was purified to 660-fold by a combination of sequential saturated ammonium sulphate precipitation and gel filtration chromatography in the FPLC system. The homogeneity of the purified lectin was established by analytical isoelectrofocusing [pI 6.75]. Hemagglutination of rabbit erythrocytes by the purified lectin was best inhibited by fetuin. The N-terminal sequence of the 41.7 kDa subunit showed homology to the outermembrane porins and the 23.4 kDa subunit showed homology to a hypothetical protein of Yersinia pestis and secreted Hcp protein. This protein could induce extensive morphological changes in HEp-2 cells and significant amount of fluid accumulation in rabbit ileal loop. GM1 showed maximum binding to the lectin among all other gangliosides. This purified protein showed cross-reactivity to the binding subunit of cholera toxin in western immunoblot. The presence of this toxin in some of the clinical isolates of enteroaggregative E. coli was also observed. The structural and functional characteristics of the toxin revealed that it is a novel virulence determinant of aggregative E. coli.

Molecular epidemiology of the iron utilization genes of enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) strains are etiologic agents of acute and persistent diarrhea. In this study, the results of phenotypic assays suggested that EAEC strains possess specialized iron acquisition systems. Genes required for the synthesis (iucA) or transport (fepC) of siderophores, and genes encoding siderophore (fyuA, ireA, and iroN) or heme transport (chu) receptors or hemoglobin proteases (pic and hbp), were sought in EAEC strains which have been characterized with respect to known virulence genes and phylogeny. The chuA, iucA, fyuA, fepC, and pic genes were detected in 33, 76.2, 85.7, 33, and 61.9% of these EAEC strains, respectively, and the other genes were absent. The majority of EAEC strains possessed genes encoding multiple iron transport systems, and there was no phylogenetic correlation in the distribution of the majority of these loci, as is typical for EAEC. The notable exceptions were chuA and fepC (which is associated with the prrA-modA-fepC pathogenicity island); these genes were restricted to the EAEC2 and DAEC2 phylogenetic groups, which could represent pathogenic subsets. When collections of EAEC strains isolated during case-control studies in Nigeria and Brazil were examined, no association of the presence of either chuA or iucA alone with diarrhea was seen, but both genes together were present in significantly more strains from cases than from controls in the Nigerian collection (P < 0.05). It is possible that the presence of both genes marks at least some virulent strains. The data also demonstrate geographical variation in the association of iron utilization genes with disease in EAEC.

Typical enteroaggregative Escherichia coli is the most prevalent pathotype among E. coli strains causing diarrhea in Mongolian children

Diarrhea remains one of the main sources of morbidity and mortality in the world, and a large proportion is caused by diarrheagenic Escherichia coli. In Mongolia, the epidemiology of diarrheagenic E. coli has not been well studied. A total of 238 E. coli strains from children with sporadic diarrhea and 278 E. coli strains from healthy children were examined by PCR for 10 virulence genes: enteropathogenic E. coli (EPEC) eae, tir, and bfpA; enterotoxigenic E. coli (ETEC) lt and st; enteroinvasive E. coli (EIEC) ipaH; enterohemorragic E. coli stx1 and stx2; and enteroaggregative E. coli (EAEC) aggR and astA. EAEC strains without AggR were identified by the HEp-2 cell adherence test. The detection of EAEC, ETEC, EPEC, and EIEC was significantly associated with diarrhea. The incidence of EAEC (15.1%), defined by either a molecular or a phenotypic assay, was higher in the diarrheal group than any other category (0 to 6.0%). The incidence of AggR-positive EAEC in the diarrheal group was significantly higher than in the control group (8.0 versus 1.4%; P = 0.0004), while that of AggR-negative EAEC was not (7.1 versus 4.3%). Nineteen AggR-positive EAEC strains harbored other EAEC virulence genes-aggA, 2 (5.5%); aafA, 4 (11.1%); agg-3a, 5 (13.8%); aap, 8 (22.2%); aatA, 11 (30.5%); capU, 9 (25.0%); pet, 6 (16.6%); and set, 3 (8.3%)-and showed 15 genotypes. EAEC may be an important pathogen of sporadic diarrhea in Mongolian children. Genetic analysis showed the heterogeneity of EAEC but illustrated the importance of the AggR regulon (denoting typical EAEC) as a marker for virulent EAEC strains.

Enteroaggregative Escherichia coli: an emerging enteric pathogen

Enteroaggregative Escherichia coli (EAEC) represents an emerging pathogen that causes enteric and food-borne infectious diseases. Subgroups in many populations throughout the world are susceptible to EAEC infection. EAEC pathogenesis involves adherence to the intestinal mucosa; increased production and deposition of a mucus biofilm; and mucosal toxicity due to inflammation and cytokine release. Due to the heterogeneity of EAEC strains and differing host immune responses, not all EAEC infections are symptomatic. Recent data suggest that individuals with a homozygous genotype -251 AA single nucleotide polymorphism (SNP), in the IL-8 promoter region, are more susceptible to EAEC diarrhea. The HEp-2 cell adherent assay allows identification of EAEC's characteristic aggregative or "stacked brick" adherence pattern. Antimicrobial treatment of individuals who develop EAEC diarrhea should be individually based. Ciprofloxacin and rifaximin, compared to placebo, have been shown to significantly shorten the course of diarrhea in patients who developed EAEC infection. The objective of this review is to increase awareness of this important emerging pathogen and to discuss the epidemiology, pathogenesis, and host-pathogen factors associated with EAEC infection.

Etiology of acute diarrhea in adults in southwestern Nigeria

Stool specimens from 113 adult outpatients with diarrhea in southwestern Nigeria and 63 controls were examined for bacterial and parasitic enteric pathogens. Enterohemorrhagic Escherichia coli (EHEC) (P < 0.02), enteroaggregative E. coli (EAEC) (P < 0.02), and Entamoeba histolytica (P < 0.0002) were significantly associated with diarrhea. Salmonella, Shigella, nontoxigenic Vibrio cholerae, other categories of diarrheagenic E. coli, as well as a variety of helminths were recovered more frequently from the stools of patients than from the stools of controls but did not show a significant association with disease. Multiple pathogens were recovered from 36.3% of specimens, and bloody diarrhea was commonly associated with E. histolytica and diarrheagenic E. coli infections. The majority of EHEC isolates were non-O157 strains that carried the stx(2) gene. Of the 23 EHEC-infected patients, 12 (52.2%) presented during the 10th week of the study. EHEC strains isolated within this cluster were more likely to hybridize with the enterohemolysin gene probe, to be nonmotile and sorbitol positive, and to fail to agglutinate O157 antisera. Pulsed-field gel electrophoresis demonstrated that the only strains with XbaI profiles that occurred more than once were isolated during the 10th and 11th weeks of the study, suggesting an outbreak. The study has demonstrated that E. histolytica, EHEC, and EAEC are important diarrheal pathogens within the study area and that sporadic and epidemic EHEC infections occur in developing as well as developed countries. Routine surveillance for diarrheagenic E. coli, even only at the tertiary-care level, would be useful in identifying outbreaks and assist in identifying environmental reservoirs and transmission routes.

Enteroaggregative and cell-detachingEscherichia coli strains among polish children with and without diarrhea

To determine the association of enteroaggregative (EAEC) and cell-detaching (CDEC) Escherichia coli with diarrhea of unknown origin among children from Wrocław (Poland), E. coli strains isolated from stool specimens of children with diarrhea were examined for mannose-resistant adherence to HEp-2 cells. EAEC were isolated from 10 of 39 (26%) children examined with diarrhea and 4 of 20 (20%) age-matched controls. CDEC were present in 14 (36%) cases of diarrhea and 7 (35%) healthy subjects. Cell-detaching activity was distinctly associated with hemolysin production. Among hemolytic CDEC strains cytotoxic necrotizing factor 1 (CNF1) synthesis prevailed among isolates obtained from cases of diarrhea (57%) in comparison with isolates obtained from healthy controls (14.3%). Although neither EAEC nor CDEC E. coli strains were associated with diarrhea of children in this setting, there were differences among EAEC and CDEC strains isolated from children with and without diarrhea.