Genetic relatedness and virulence properties of enteropathogenic Escherichia coli strains of serotype O119:H6 expressing localized adherence or localized and aggregative adherence-like patterns on HeLa cells

Virulence Potential of a Multidrug-Resistant Escherichia coli Strain Belonging to the Emerging Clonal Group ST101-B1 Isolated from Bloodstream Infection

Escherichia coli EC121 is a multidrug-resistant (MDR) strain isolated from a bloodstream infection of an inpatient with persistent gastroenteritis and T-zone lymphoma that died due to septic shock. Despite causing an extraintestinal infection, previous studies showed that it did not have the usual characteristics of an extraintestinal pathogenic E. coli. Instead, it belonged to phylogenetic group B1 and harbored few known virulence genes. To evaluate the pathogenic potential of strain EC121, an extensive genome sequencing and in vitro characterization of various pathogenicity-associated properties were performed. The genomic analysis showed that strain EC121 harbors more than 50 complete virulence genetic clusters. It also displays the capacity to adhere to a variety of epithelial cell lineages and invade T24 bladder cells, as well as the ability to form biofilms on abiotic surfaces, and survive the bactericidal serum complement activity. Additionally, EC121 was shown to be virulent in the Galleria mellonella model. Furthermore, EC121 is an MDR strain harboring 14 antimicrobial resistance genes, including bla_CTX-M-2. Completing the scenario, it belongs to serotype O154:H25 and to sequence type 101-B1, which has been epidemiologically linked to extraintestinal infections as well as to antimicrobial resistance spread. This study with E. coli strain EC121 shows that clinical isolates considered opportunistic might be true pathogens that go underestimated.

Phenotypic characterization and virulence-related properties of Escherichia albertii strains isolated from children with diarrhea in Brazil

Escherichia albertii are emerging enteropathogens, whose identification is difficult, as they share biochemical characteristics and some virulence-related genes with diarrheagenic Escherichia coli (DEC). Studies on phylogeny, phenotypic characteristics and potential virulence factors of human E. albertii strains are scarce. In this study, we identified by multiplex PCR five E. albertii among 106 strains isolated from diarrheic children in São Paulo, Brazil, which were previously classified as atypical enteropathogenic E. coli. All strains were investigated regarding their phylogeny, biochemical properties, virulence-related properties, antimicrobial resistance and presence of putative virulence-related genes. All strains belonged to different E. albertii lineages and adhered to and produced attaching and effacing lesions on HeLa cells. Three strains invaded Caco-2 cells, but did not persist intracellularly, and three formed biofilms on polystyrene surfaces. All strains were resistant to few antibiotics and only one carried a self-transmissible resistance plasmid. Finally, among 38 DEC and 18 extraintestinal pathogenic E. coli (ExPEC) virulence-related genes searched, six and three were detected, respectively, with paa and cdtB being found in all strains. Despite the limited number of strains, this study provided additional knowledge on human E. albertii virulence potential, showing that they share important virulence factors with DEC and ExPEC.

Molecular and phenotypic characterization of diarrheagenic Escherichia coli isolated from groundwater in rural areas in southern Brazil

Water-borne diseases like diarrheagenic Escherichia coli (DEC)-induced gastroenteritis are major public health problems in developing countries. In this study, the microbiological quality of water from mines and shallow wells was analyzed for human consumption. Genotypic and phenotypic characterization of DEC strains was performed. A total of 210 water samples was analyzed, of which 153 (72.9%) contained total coliforms and 96 (45.7%) E. coli. Of the E. coli isolates, 27 (28.1%) contained DEC genes. The DEC isolates included 48.1% Shiga toxin-producing E. coli (STEC), 29.6% enteroaggregative E. coli (EAEC), 14.9% enteropathogenic E. coli (EPEC), 3.7% enterotoxigenic E. coli (ETEC), and 3.7% enteroinvasive E. coli (EIEC). All the STECs had cytotoxic effects on Vero cells and 14.8% of the DEC isolates were resistant to at least one of the antibiotics tested. All DEC formed biofilms and 92.6% adhered to HEp-2 cells with a prevalence of aggregative adhesion (74%). We identified 25 different serotypes. One EPEC isolate was serotype O44037:H7, reported for the first time in Brazil. Phylogenetically, 63% of the strains belonged to group B1. The analyzed waters were potential reservoirs for DEC and could act as a source for infection of humans. Preventive measures are needed to avoid such contamination.

Diversity of strategies used by atypical enteropathogenic Escherichia coli to induce attaching and effacing lesion in epithelial cells

PURPOSE

This study aimed to characterize 82 atypical enteropathogenic Escherichia coli (aEPEC) isolates, obtained from patients with diarrhea in Brazil, regarding their adherence patterns on HeLa cells and attaching and effacing (AE) lesion pathways.

METHODOLOGY

The adherence and fluorescence-actin staining (FAS) assays were performed using HeLa cells. AE lesion pathways were determined through the detection of tyrosine residue 474 (Y474) phosphorylation in the Tir protein, after its translocation to host cells, and by PCR assays for tir genotyping and detection of Tir-cytoskeleton coupling protein (tccP) genes.

RESULTS

Regarding the adherence pattern, determined in the presence of d-mannose, 12 isolates (14.6 %) showed the localized adherence (LA)-like pattern, 3 (3.7  %) the aggregative adherence pattern and 4 (4.9  %) a hybrid LA/diffuse adherence pattern. In addition, 36 (43.9  %) isolates displayed an undefined adherence, and 26 (31.7  %) were non-adherent (NA), while one (1.2 %) caused cell detachment. Among the 26 NA aEPEC isolates, 11 showed a type 1 pilus-dependent adherence in assays performed without d-mannose, while 15 remained NA. Forty-eight (58.5 %) aEPEC were able to trigger F-actin accumulation underneath adherent bacteria (FAS-positive), which is an important feature of AE lesions. The majority (58.3 %) of these used the Tir-Nck pathway, while 39.6  % may use both Tir-Nck and Tir-TccP pathways to induce AE lesions.

CONCLUSION

Our results reveal the diversity of strategies used by aEPEC isolates to interact with and damage epithelial host cells, thereby causing diarrheal diseases.

Distribution of the pilS gene in Escherichia coli pathovars, its transfer ability and influence in the typical enteropathogenic E. coli adherence phenotype

Typical enteropathogenic Escherichia coli strains (tEPEC) cause attaching/effacing lesions in eukaryotic cells and produce the bundle-forming pilus (BFP), which interweaves and aggregates bacteria, resulting in the localized adherence (LA) pattern on eukaryotic cells. Previously, we identified tEPEC strains (serotype O119:H6) that exhibited LA simultaneously with an aggregative adherence (AA)-like pattern (LA/AA-like+). Remarkably, AA is characteristically produced by strains of enteroaggregative E. coli (EAEC), another diarrheagenic E. coli pathovar. In one LA/AA-like + strain (Ec404/03), we identified a conjugative plasmid containing the pil operon, which encodes the Pil fimbriae. Moreover, a pil operon associated with an AA pattern and plasmid transfer had been previously described in the EAEC C1096 strain. In this study, we investigated the occurrence of the two pilS alleles (pilS_Ec404 and pilS_C1096) in tEPEC strains of different serotypes, origins and years of isolation. We also examined the potential relationship of pilS with the AA-like phenotype, its ability to be transferred by conjugation, and occurrence among strains of the other E. coli pathovars. The pilS alleles were found in 90 (55.2%) of 163 tEPEC strains, with pilS_Ec404 occurring more often (30.7%) than pilS_C1096 (25.1%). About 21 tEPEC serotypes carried pilS. The pilS alleles were found in tEPEC strains from Chile, Peru and different Brazilian cities, with the oldest strain being isolated in 1966. No absolute correlation was found between the presence of pilS and the AA-like pattern. Conjugative pilS transfer was detected in 26.2% of pilS_Ec404+ strains and in 65.1% of pilS_C1096+ strains, but only pilS_Ec404+ transconjugants were AA-like+, thus suggesting that the latter allele might need a different genetic background to express this phenotype. pilS was found in all other E. coli pathovars, where it was most prevalent in enterotoxigenic E. coli. More studies are needed to understand the mechanisms involved in the regulation of Pil expression and production.

Novel Hybrid of Typical Enteropathogenic Escherichia coli and Shiga-Toxin-Producing E. coli (tEPEC/STEC) Emerging From Pet Birds

Exotic psittacine birds have been implicated as reservoir of diarrheagenic Escherichia coli (E. coli), including enteropathogenic E. coli (EPEC) and Shiga-toxin producing E. coli (STEC). Here, we present a genotypic and phenotypic characterization of typical EPEC/STEC hybrid strains isolated from exotic psittacine birds. The strains were positive for eae, bfpA, and stx2f genes, belong to serotype O137:H6 and ST2678. Two strains were subject to whole genome sequencing, confirming the presence of the virulence factors of both E. coli pathotypes. Phenotypical in vitro tests confirmed their ability to adhere to HeLa cells and cause cytotoxicity to Vero cells. The rabbit ileal loop assays showed the attaching and effacing lesion, in addition to inflammatory process and overproduction of intestinal mucus. This is the first report of hybrid typical EPEC/STEC (O137:H6/ST2678) strains isolated from companion psittacine birds and the results suggest zoonotic risks.

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.

Phylogenetic Analysis of Enteroaggregative Escherichia coli (EAEC) Isolates from Japan Reveals Emergence of CTX-M-14-Producing EAEC O25:H4 Clones Related to Sequence Type 131

Enteroaggregative Escherichia coli (EAEC) causes acute or persistent diarrhea. The aggR gene is widely used as a marker for typical EAEC. The heterogeneity of EAEC is well known; however, there are few reports on the phylogenetic relationships of EAEC. Recently, CTX-M extended-spectrum β-lactamase (ESBL)-producing EAEC strains have been reported worldwide. To characterize EAEC strains in Japan, we investigated the population structure of EAEC. A total of 167 aggR-positive strains isolated from stool specimens from diarrheal patients in Kagoshima (139 strains) and Osaka (28 strains), Japan, between 1992 and 2010 were examined for the prevalence of EAEC virulence markers, the blaCTX-M gene, and the capacity to form biofilms. Multilocus sequence typing was also conducted. EAEC strains were widely distributed across four major E. coli phylogroups. Strains of O111:H21/clonal group 40 (CG40) (30 strains), O126:H27/CG200 (13 strains), and O86a:H27/CG3570 (11 strains) in phylogroup B1 are the historical EAEC clones in Japan, and they exhibited strong biofilm formation. Twenty-nine strains of EAEC O25:H4/CG131 were identified in phylogroup B2, 79% of which produced CTX-M-14. This clone has emerged since 2003. The clone harbored plasmid-encoded EAEC virulence genes but not chromosomal virulence genes and had lower biofilm-forming capacity than historical EAEC strains. This clone most likely emerged from a pandemic uropathogenic O25:H4/sequence type 131 clone by acquiring an EAEC virulence plasmid from canonical EAEC. Surveillance of the horizontal transfer of both virulence and ESBL genes among E. coli strains is important for preventing a worldwide increase in antimicrobial drug resistance.