Evidence of pathogenic subgroups among atypical enteropathogenic Escherichia coli strains

Genotypic and Phenotypic Characterization of Pathogenic Escherichia coli, Salmonella spp., and Campylobacter spp., in Free-Living Birds in Mainland Portugal

Birds are potential carriers of pathogens affecting humans and agriculture. Aiming to evaluate the occurrence of the top three most important foodborne pathogens in free-living birds in Portugal, we investigated 108 individual fecal samples from free-living birds and one pooled sample of gull feces (n = 50) for the presence of Escherichia coli (pathogenic and non-pathogenic), Salmonella spp. and Campylobacter spp. Virulence- and antimicrobial resistance- (AMR) associated genes were detected by PCR and Whole-Genome Sequencing (WGS), and phenotypic (serotyping and AMR profiles) characterization was performed. Overall, 8.9% of samples tested positive for pathogenic E. coli, 2.8% for Salmonella spp., and 9.9% for Campylobacter spp. AMR was performed on all pathogenic isolates and in a fraction of non-pathogenic E. coli, being detected in 25.9% of them. Ten of the tested E. coli isolates were multidrug-resistant (MDR), and seven of them were Extended-spectrum β-lactamase (ESBL) producers. Among Salmonella (n = 3) and Campylobacter (n = 9), only one strain of C. jejuni was identified as MDR. Most of the identified serotypes/sequence types had already been found to be associated with human disease. These results show that free-living birds in Portugal may act as carriers of foodborne pathogens linked to human disease, some of them resistant to critically important antimicrobials.

Quantitative analysis and virulence phenotypes of atypical enteropathogenic Escherichia coli (EPEC) acquired from diarrheal stool samples from a Midwest US hospital

Infectious diarrhea causes approximately 179 million illnesses annually in the US. Multiplex PCR assays for enteric pathogens detect enteropathogenic Escherichia coli (EPEC) in 12-29% of diarrheal stool samples from all age groups in developed nations. The aim of this study was to isolate and characterize EPEC from diarrhea samples identified as EPEC positive by BioFire Gastrointestinal Panel (GIP). EPEC is the second most common GIP-detected pathogen, equally present in sole and mixed infections peaking during summer months. EPEC bacterial load is higher in samples with additional pathogens. EPEC-GIP-positive stool samples were cultured on MacConkey II agar and analyzed by colony PCR for eaeA and bfpA to identify and classify EPEC isolates as typical (tEPEC) or atypical (aEPEC). EPEC were not recovered from the majority of stool samples with only 61 isolates obtained from 277 samples; most were aEPEC from adults. bfpA-mRNA was severely diminished in 3 of 4 bfpA-positive isolates. HeLa and SKCO-15 epithelial cells were infected with EPEC isolates and virulence-associated phenotypes, including adherence pattern, attachment level, pedestal formation, and tight junction disruption, were assessed. All aEPEC adherence patterns were represented with diffuse adherence predominating. Attachment rates of isolates adhering with defined adherence patterns were higher than tEPEC lacking bfpA (ΔbfpA). The majority of isolates formpedestals. All but one isolate initially increases but ultimately decreases transepithelial electrical resistance of SKCO-15 monolayers, similar to ΔbfpA. Most isolates severely disrupt occludin; ZO-1 disruption is variable. Most aEPEC isolates induce more robust virulence-phenotypes in vitro than ΔbfpA, but less than tEPEC-E2348/69.

Comparative genomic analysis provides insight into the phylogeny and virulence of atypical enteropathogenic Escherichia coli strains from Brazil

Background

Atypical enteropathogenic Escherichia coli (aEPEC) are one of the most frequent intestinal E. coli pathotypes isolated from diarrheal patients in Brazil. Isolates of aEPEC contain the locus of enterocyte effacement, but lack the genes of the bundle-forming pilus of typical EPEC, and the Shiga toxin of enterohemorrhagic E. coli (EHEC). The objective of this study was to evaluate the phylogeny and the gene content of Brazilian aEPEC genomes compared to a global aEPEC collection.

Methodology

Single nucleotide polymorphism (SNP)-based phylogenomic analysis was used to compare 106 sequenced Brazilian aEPEC with 221 aEPEC obtained from other geographic origins. Additionally, Large-Scale BLAST Score Ratio was used to determine the shared versus unique gene content of the aEPEC studied.

Principal Findings

Phylogenomic analysis demonstrated the 106 Brazilian aEPEC were present in phylogroups B1 (47.2%, 50/106), B2 (23.6%, 25/106), A (22.6%, 24/106), and E (6.6%, 7/106). Identification of EPEC and EHEC phylogenomic lineages demonstrated that 42.5% (45/106) of the Brazilian aEPEC were in four of the previously defined lineages: EPEC10 (17.9%, 19/106), EPEC9 (10.4%, 11/106), EHEC2 (7.5%, 8/106) and EPEC7 (6.6%, 7/106). Interestingly, an additional 28.3% (30/106) of the Brazilian aEPEC were identified in five novel lineages: EPEC11 (14.2%, 15/106), EPEC12 (4.7%, 5/106), EPEC13 (1.9%, 2/106), EPEC14 (5.7%, 6/106) and EPEC15 (1.9%, 2/106). We identified 246 genes that were more frequent among the aEPEC isolates from Brazil compared to the global aEPEC collection, including espG2, espT and espC (P<0.001). Moreover, the nleF gene was more frequently identified among Brazilian aEPEC isolates obtained from diarrheagenic patients when compared to healthy subjects (69.7% vs 41.2%, P<0.05).

Conclusion

The current study demonstrates significant genomic diversity among aEPEC from Brazil, with the identification of Brazilian aEPEC isolates to five novel EPEC lineages. The greater prevalence of some virulence genes among Brazilian aEPEC genomes could be important to the specific virulence strategies used by aEPEC in Brazil to cause diarrheal disease.

Atypical EPEC (aEPEC) is one of the most frequent diarrheagenic Escherichia coli pathotypes isolated from patients in Brazil and is associated with diarrheal outbreaks. This study is the first to sequence the genomes of a collection of aEPEC isolates from a South American country, Brazil, and compare their phylogenetic relationships and gene content with a global collection of aEPEC. This approach identified Brazilian aEPEC genomes in previously characterized EPEC/EHEC phylogenomic lineages and resulted in the identification of five novel EPEC phylogenomic lineages, designated EPEC11 to EPEC15. We also observed that virulence genes, such as espG2, espT and espC were more frequently identified among the Brazilian aEPEC genomes, demonstrating potential differences in the virulence repertoire of this pathogen in Brazil.

Large plasmids encoding antibiotic resistance and localized-like adherence in atypical enteropathogenic Escherichia coli strains

Background

In previous studies, we have shown that atypical enteropathogenic Escherichia coli (aEPEC) strains are important diarrheal pathogens among Brazilian children. In the characterization of a collection of 126 aEPEC strains, we identified 29 strains expressing the localized-like adherence (LAL) pattern on HEp-2 cells and harboring large plasmids in the range of 60 to 98 MDa. In this study, we examined 18 of these strains for their ability to transfer the LAL phenotype to a E. coli K-12 C600 strain.

Results

In conjugation experiments, using eight strains which were resistant to one or more antimicrobials and positive for F-pili genes (traA), we were able to cotransfer antimicrobial resistance markers along with adhesion genes. By transforming E. coli DH5α with plasmid DNA from strains A46 (pIS46), A66 (pIS66) and A102 (pIS102), we were able to demonstrate that genes encoding ampicillin, tetracycline and LAL were encoded on a 98-MDa conjugative plasmid. To identify a gene responsible for LAL, we constructed a transposon mutant library of A102 strain. Among 18 mutants that did not adhere to HeLa cells, four carried insertions within fimbrial genes (fimA and traJ) and agglutinin genes (tia and hek). Using these Tn5 mutants as donors, we were able to obtain kanamycin-resistant E. coli MA3456 transconjugants. Sequence analysis of the plasmid genes revealed a region exhibit to 80 and 73% amino acid similarities to the agglutinins Tia and Hek, respectively.

Conclusion

In this study, we have identified three large conjugative plasmids, pIS46, pIS66 and pIS102, coding for antimicrobial resistance and localized-like adherence (LAL) to HeLa cells. In addition, we identified a tia/hek homolog encoded on the pIS102 plasmid, which seems to be involved in adhesion of A102 strain.

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.

Environment Controls LEE Regulation in Enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) is a significant cause of infant morbidity and mortality in developing regions of the world. Horizontally acquired genetic elements encode virulence structures, effectors, and regulators that promote bacterial colonization and disease. One such genetic element, the locus of enterocyte effacement (LEE), encodes the type three secretion system (T3SS) which acts as a bridge between bacterial and host cells to pass effector molecules that exert changes on the host. Due to its importance in EPEC virulence, regulation of the LEE has been of high priority and its investigation has elucidated many virulence regulators, including master regulator of the LEE Ler, H-NS, other nucleoid-associated proteins, GrlA, and PerC. Media type, environmental signals, sRNA signaling, metabolic processes, and stress responses have profound, strain-specific effects on regulators and LEE expression, and thus T3SS formation. Here we review virulence gene regulation in EPEC, which includes approaches for lessening disease by exploiting the elucidated regulatory pathways.

Distribution of Major Pilin Subunit Genes Among Atypical Enteropathogenic Escherichia coli and Influence of Growth Media on Expression of the ecp Operon

Atypical enteropathogenic Escherichia coli (aEPEC) strains are unable to produce the bundle-forming pilus (BFP), which is responsible for the localized adherence pattern, a characteristic of the pathogenicity of typical EPEC strains. The lack of BFP in aEPEC strains suggests that other fimbrial or non-fimbrial adhesins are involved in their adhesion to the host cells. The aim of this study was to investigate the distribution of major subunit fimbrial genes known to be important adherence factors produced by several E. coli pathotypes in a collection of 72 aEPEC strains. Our results demonstrate that a high percentage (94–100%) of aEPEC strains harbored ecpA, fimA, hcpA, and lpfA fimbrial genes. Other fimbrial genes including pilS, pilV, sfpA, daaC, papA, and sfa were detected at lower frequencies (1–8%). Genes encoding fimbrial subunits, which are characteristic of enteroaggregative E. coli or enterotoxigenic E. coli were not found. No correlation was found between fimbrial gene profiles and adherence phenotypes. Since all aEPEC strains contained ecpA, the major pilin gene of the E. coli common pilus (ECP), a subset of ecpA+ strains was analyzed for transcription of ecpRABCDE and production of ECP upon growth in three different culture conditions at 37°C. Transcription of ecpRABCDE occurred in all conditions; however, ECP production was medium dependent. In all, the data suggest that aEPEC strains are highly heterogeneous in terms of their fimbrial gene profiles. Despite lacking BFP production, other mechanisms of cell adherence exist in aEPEC strains to ensure host colonization, e.g., mediated by other prevalent pili such as ECP. Moreover, the production of ECP by aEPEC strains might be influenced by yet unknown post-transcriptional factors.

High Prevalence of Virulence Genes in Specific Genotypes of Atypical Enteropathogenic Escherichia coli

Atypical enteropathogenic Escherichia coli (aEPEC) strains are emerging enteropathogens that have been detected worldwide. A collection of 228 aEPEC strains (121 from diarrheal patients, 27 from healthy carriers, 47 from animals and 33 from raw meats) were investigated for serotypes, virulence gene profiles and phylogenetic relationships. Sixty-six O serogroups were identified. Serogroup O51 was the most prevalent, followed by O119, O26 and O76. For the 20 virulence genes detected, statistically significant differences were observed in the overall prevalence of efa1 (lifA), nleB, nleE, set/ent, paa, and ehxA genes among strains from diarrheal patients, healthy carriers, animals and raw meats, respectively. Strains from diarrheal patients had significantly higher levels of efa1 (lifA) (29.8 vs. 0%, P = 0.0002), nleB (41.3 vs. 7.4%, P = 0.0004), nleE (43.8 vs. 7.4%, P = 0.0002) and set/ent (41.3 vs. 7.4%, P = 0.0004) genes than strains obtained from healthy carriers. The paa gene was identified more often in isolates from raw meats (63.6 vs. 14.8%, P < 0.0001), animals (42.6 vs. 14.8%, P < 0.0122), and diarrheal patients (36.4 vs. 14.8%, P < 0.0225) than in strains obtained from healthy carriers. The ehxA gene was detected more frequently in strains from raw meats than in strains from diarrheal patients (27.3 vs. 2.5%, P = 0.0000) and healthy carriers (27.3 vs. 7.4%, P = 0.0474). The phylogenetic marker, yjaA, was more frequently observed in strains among healthy carriers than in diarrheal patient strains. Among the 228 aEPEC strains, 79 sequence types (STs) were identified. The prominent STs, which comprised strains carrying the four OI-122 genes and lpfA, were ST40, ST328, and ST29. Overall, the results indicate that aEPEC strains isolated in China are highly heterogeneous. aEPEC strains that are potentially more pathogenic appear to be related to specific STs or clonal complexes and serotypes. The high prevalence of diarrhea-associated genes in animal or raw meat strains suggests a zoonotic transmission pathway for potentially human pathogenic aEPEC.

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.

Characterization of the universal stress protein F from atypical enteropathogenic Escherichia coli and its prevalence in Enterobacteriaceae

Atypical enteropathogenic Escherichia coli (aEPEC) are heterogeneous strains in terms of serotypes, adherence patterns and the presence of novel virulence factors. This heterogeneity is intriguing, promoting studies trying to characterize these novel proteins and to better comprehend this pathotype group. In a previous study analyzing low-molecular mass proteomes of four representative aEPEC strains of three different adhesion phenotypes, we classified proteins according to their annotated function, with most of them being involved in metabolism and transport; while some of them were classified as hypothetical proteins. The majority of the hypothetical proteins were homologue products of genes identified in the genome of enterohemorrhagic E. coli. One of the hypothetical proteins was annotated as Z2335, with orthologue in EPEC, and by bioinformatics analysis, this protein was revealed to be the universal stress protein F (UspF). Thus, herein we successfully obtained a recombinant UspF protein from aEPEC, which is a α/β, ATP-binding protein involved in stress response, with comparable protein production among the four studied strains, but showing noteworthy differences when cultivated in different stress conditions, also present in other enterobacterial species, such as Shigella sonnei and Citrobacter freundii. Furthermore, our results confirm that the Usp protein superfamily encompasses a conserved group of proteins involved in stress resistance in aEPEC and other Enterobacteriaceae.

Genetic characterization of Shiga toxin-producing Escherichia coli (STEC) and atypical enteropathogenic Escherichia coli (EPEC) isolates from goat's milk and goat farm environment

The aim of this study was to characterize a collection of 44 Shiga toxin-producing (STEC) and enteropathogenic Escherichia coli (EPEC) isolated from goat milk and goat farm environment. Of the 19 STEC isolates, five (26.3%) carried the stx1 gene, four (21.1%) the stx2 gene and 10 (52.6%) presented both stx genes. Six (31.6%) STEC strains were eae-positive and belonged to serotypes related to severe human disease (O157:H7 and O5:HNM). Another seven STEC strains were of serotype O146:H21 and three of serotype O166:H28, also linked to human disease. The STEC strains isolated from goat milk were of serotypes potentially pathogenic for humans. All the 25 EPEC isolates were considered atypical (aEPEC) and one aEPEC strain was of serotype O26:H11, a serotype frequently isolated in children with diarrhea. Multilocus sequence typing (MLST) was carried out with seven housekeeping genes and 23 sequence types (ST) were detected, 14 of them newly described. Twelve STs grouped STEC isolates and 11 STs grouped EPEC isolates. Genetic typing by pulsed field gel electrophoresis (PFGE) resulted in 38 patterns which grouped in 10 clusters. Well-defined groups were also observed for strains of pathogenic serotypes. In conclusion, strains of STEC and aEPEC belonging to serotypes related to severe human disease have been detected in goat milk and the goat farm environment. Ruminants are an important reservoir of STEC strains and the role of these animals as carriers of other pathogenic types of E. coli seems to be an emerging concern.

Atypical enteropathogenic Escherichia coli as aetiologic agents of sporadic and outbreak-associated diarrhoea in Brazil

Enteropathogenic Escherichia coli (EPEC) are important agents of diarrhoea in industrialized as well as developing countries, such as Brazil. The hallmark of EPEC pathogenesis is the establishment of attaching and effacing lesions in enterocytes, in which pedestal-like structures are formed underneath adherent bacteria. EPEC are divided into two subgroups, typical (tEPEC) and atypical (aEPEC), based on the presence of the EPEC adherence factor plasmid in tEPEC and its absence in aEPEC. This study was designed to characterize 82 aEPEC isolates obtained from stool samples of diarrhoeic patients during 2012 and 2013 in Brazil. The majority of the aEPEC were assigned to the phylo-group B1 (48.8 %), and intimin subtypes θ (20.7 %), β1 (9.7 %) and λ (9.7 %) were the most prevalent among the isolates. The nleB and nleE genes were concomitantly detected in 32.9 % of the isolates, demonstrating the occurrence of the pathogenicity island O122 among them. The O157-plasmid genes (ehxA and/or espP) were detected in 7.3 % of the isolates, suggesting that some aEPEC could be derived from Shiga-toxin-producing E. coli that lost the stx genes while trafficking in the host. PFGE of 14 aEPEC of serotypes O2 : H16, O33 : H34, O39 : H9, O108 : H- and ONT : H19 isolated from five distinct outbreaks showed serotype-specific PFGE clusters, indicating a high degree of similarity among the isolates from the same event, thus highlighting these serotypes as potential aetiologic agents of diarrhoeal outbreaks in Brazil.

Shiga Toxigenic Escherichia coli in Iranian Pediatric Patients With and Without Diarrhea: O-Serogroups, Virulence Factors and Antimicrobial Resistance Properties

Background:

Shiga-toxigenic Escherichia coli is an important human pathogen cause of diarrhea, hemorrhagic colitis, hemolytic uremic syndrome and thrombotic thrombocytopenic purpura in humans is a significant public health.

Objectives:

The aim of this study was to determine the molecular characteristics and antimicrobial resistance properties of Shiga toxigenic Escherichia coli (STEC) strains with respect to their seasonal, age and geographical distributions in Iranian pediatric patients with and without diarrhea.

Patients and Methods:

Four hundred and eighty swab samples were taken from pediatric patients with and without diarrhea of four major provinces of Iran. Swab samples were immediately cultured and the positive culture samples were analyzed by the polymerase chain reaction (PCR) method. Finally, antimicrobial susceptibility testing was performed using the disk diffusion method in Mueller-Hinton agar.

Results:

In total, 118 out of 200 diarrheic stool samples (59%) and 77 out of 280 non-diarrheic stool samples (27.5%) were positive for E. coli. Samples taken from one to ten months old cases (73.33%) and those from Shiraz province (81.13%) were the most commonly infected. Samples taken in the summer season (91.66%) were the most commonly infected. A significant difference was shown between AEEC and EHEC strains of E. coli. The genes encoding Shiga toxins and intimin protein were the most commonly detected in all strains. O26 (33.33%), O111 (18.18%) and O91 (12.12%) serogroups had the highest incidence in patients with and without diarrhea. Prevalence of the genes that encode resistance against ampicillin (CITM), gentamicin (aac(3)-IV) and tetracycline (tetA) were 80.30%, 75.75% and 65.15%, respectively. The STEC strains harbored the highest levels of resistance against ampicillin (84.84%), gentamycin (78.78%), tetracycline (50%) and sulfamethoxazole (40.90%) antibiotics. We found that 55.08% of diarrheic and 1.29% of non-diarrheic E. coli isolates were resistant to more than six antibiotics.

Conclusions:

Accurate control programs should be organized for antibiotic prescription especially during warmer seasons in Iran. Primary treatment of diarrheic patients with co-trimoxazole, cefotaxime and ceftriaxone is effective.

Genetic analysis of enteropathogenic Escherichia coli (EPEC) adherence factor (EAF) plasmid reveals a new deletion within the EAF probe sequence among O119 typical EPEC strains

Background

Enteropathogenic Escherichia coli (EPEC) are classified into typical and atypical strains based on the presence of the E. coli adherence factor (EAF) plasmid. The EAF plasmid contains the bfp (bundle-forming pilus) operon and the perABC (plasmid encoded regulator) gene cluster. A 1-kb cryptic region of EAF plasmid has been widely used as a genetic probe for EPEC detection. However, some EPEC strains may harbor an EAF plasmid lacking the EAF probe sequence, which makes the differentiation between typical and atypical a complex task. In this study, we report the genetic analysis of the EAF plasmid-encoded genes in a collection of EPEC clinical isolates.

Methods

A total of 222 EPEC clinical isolates, which were previously classified as typical (n = 70) or atypical (n = 152) by EAF probe reactivity, were screened for the presence of different EAF sequences by PCR and DNA hybridization.

Results

All typical strains possessed intact bfpA and perA genes, and most of them were positive in the PCR for EAF probe sequence. However, a subset of 30 typical strains, 22 of which belonged to O119 serogroup, presented a 1652 pb deletion in the region between 1093-bp downstream perC and 616-bp of the EAF fragment. The bfpA, bfpG, and per genes were found in all typical strains. In addition, 32 (21 %) atypical strains presented the perA gene, and 20 (13.2 %) also presented the bfpA gene. Among the 32 strains, 16 belonged to the O119:H2, O119:HND, and ONT:HND serotypes. All 32 atypical strains contained perA mutation frameshifts and possessed an IS1294 element upstream of the per operon as detected by PCR followed by restriction fragment length polymorphism (RFLP) typing and multiplex PCR. Among the 20 bfpA probe-positive strains, eight O119 strains possessed deletion in the bfp operon at the 3′end of bfpA due to an IS66 element.

Conclusion

Our data show that typical O119 strains may contain a deletion within the EAF probe sequence not previously reported. This new finding suggests that care should be taken when using the previously described EAF PCR assay in epidemiological studies for the detection of typical O119 strains. In addition, we were able to confirm that some atypical strains carry vestiges of the EAF plasmid.

Distribution of non-LEE-encoded type 3 secretion system dependent effectors in enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) are important human gastroenteritis agents. The prevalence of six non-LEE genes encoding type 3 translocated effectors was investigated. The nleC, cif and nleB genes were more prevalent in typical than in atypical EPEC, although a higher diversity of genes combinations was observed in atypical EPEC.

Phenotypic and genotypic characteristics associated with biofilm formation in clinical isolates of atypical enteropathogenic Escherichia coli (aEPEC) strains

BACKGROUND

Biofilm formation by enteropathogenic Escherichia coli (EPEC) have been recently described in the prototype typical EPEC E2348/69 strain and in an atypical EPEC O55:H7 strain. In this study, we sought to evaluate biofilm formation in a collection of 126 atypical EPEC strains isolated from 92 diarrheic and 34 nondiarrheic children, belonging to different serotypes. The association of biofilm formation and adhesin-related genes were also investigated.

RESULTS

Biofilm formation occurred in 37 (29%) strains of different serotypes, when the assays were performed at 26°C and 37°C for 24 h. Among these, four strains (A79, A87, A88, and A111) formed a stronger biofilm than did the others. The frequency of biofilm producers was higher among isolates from patients compared with isolates from controls (34.8% vs 14.7%; P = 0.029). An association was found between biofilm formation and expression of type 1 fimbriae and curli (P < 0.05). Unlike the previously described aEPEC O55:H7, one aEPEC O119:HND strain (A111) formed a strong biofilm and pellicle at the air-liquid interface, but did not express curli. Transposon mutagenesis was used to identify biofilm-deficient mutants. Transposon insertion sequences of six mutants revealed similarity with type 1 fimbriae (fimC, fimD, and fimH), diguanylate cyclase, ATP synthase F1, beta subunit (atpD), and the uncharacterized YjiC protein. All these mutants were deficient in biofilm formation ability.

CONCLUSION

This study showed that the ability to adhere to abiotic surfaces and form biofilm is present in an array of aEPEC strains. Moreover, it seems that the ability to form biofilms is associated with the presence of type 1 fimbriae and diguanylate cyclase. Characterization of additional biofilm formation mutants may reveal other mechanisms involved in biofilm formation and bring new insights into aEPEC adhesion and pathogenesis.

Detection and genetic analysis of the enteroaggregative Escherichia coli heat-stable enterotoxin (EAST1) gene in clinical isolates of enteropathogenic Escherichia coli (EPEC) strains

Background

The enteroaggregative E. coli heat-stable enterotoxin 1 (EAST1) encoded by astA gene has been found in enteropathogenic E. coli (EPEC) strains. However, it is not sufficient to simply probe strains with an astA gene probe due to the existence of astA mutants (type 1 and type 2 SHEAST) and EAST1 variants (EAST1 v1-4). In this study, 222 EPEC (70 typical and 152 atypical) isolates were tested for the presence of the astA gene sequence by PCR and sequencing.

Results

The astA gene was amplified from 54 strains, 11 typical and 43 atypical. Sequence analysis of the PCR products showed that 25 strains, 7 typical and 18 atypical, had an intact astA gene. A subgroup of 7 atypical strains had a variant type of the astA gene sequence, with four non-synonymous nucleotide substitutions. The remaining 22 strains had mutated astA gene with nucleotide deletions or substitutions in the first 8 codons. The RT-PCR results showed that the astA gene was transcribed only by the strains carrying either the intact or the variant type of the astA gene sequence. Southern blot analysis indicated that astA is located in EAF plasmid in typical strains, and in plasmids of similar size in atypical strains. Strains carrying intact astA genes were more frequently found in diarrheic children than in non-diarrheic children (p < 0.05).

Conclusion

In conclusion, our data suggest that the presence of an intact astA gene may represent an additional virulence determinant in both EPEC groups.

Detection of Shiga toxigenic (STEC) and enteropathogenic (EPEC) Escherichia coli in dairy buffalo

Enteropathogenic (EPEC) and Shiga toxigenic (STEC) Escherichia coli are among the bacteria most associated with enteric diseases in man. The aims of this study were to determine the prevalence of STEC and EPEC in dairy buffalo and then characterize these isolates genetically. To determine the prevalence of these bacteria, samples were collected from the feces and milk of buffaloes. In total, 256 samples were collected in 3 samplings, of which 76 samples tested positive for either the stx1, stx2 or eae genes or a combination thereof. From the positive samples, 22 STEC and 11 atypical EPEC (aEPEC) isolates were obtained. The isolates showed 23 different genetic profiles. No profile was very frequent in STEC isolates. On the other hand, the profile eae+, ehxA+, iha+, efa1+, toxB+, paa+, lpfAO113+ was found in 45% of the aEPEC isolates. In addition to stx1, stx2 and eae, the genes ehxA, efa1, saa, lpfAO113, lpfAO157/OI-141, lpfAO157/OI-154, toxB and iha were present in the isolates. Serogroup O26 was found in 26% of the aEPEC. Other serogroups detected include O87, O145, O176 and O179. The isolates were sensitive to almost all drugs tested and some isolates shared the same fingerprint patterns by enterobacterial repetitive intergenic consensus sequence-PCR (ERIC-PCR). The results suggest that, besides major reservoirs of STEC, buffaloes are also aEPEC reservoirs. The detection of a serogroup (O26), and putative virulence genes (efa1 ehxA, paa and lpfAO113), previously associated with aEPEC isolated from humans with diarrhea in aEPEC from buffaloes should be studied further.

Serogroups, virulence genes and antibiotic resistance in Shiga toxin-producing Escherichia coli isolated from diarrheic and non-diarrheic pediatric patients in Iran

Background

From a clinical perspective, it is important to know which serogroups, virulence genes and antibiotic resistance patterns are present in Shiga toxin-producing Escherichia coli strains in pediatric patients suffering from diarrheic and non-diarrheic infections. This is the first study in Iran that has comprehensively investigated the Shiga toxin-producing Escherichia coli -related infection characteristics in diarrheic and non-diarrheic pediatric patients of 0–60 months of age.

Methods

Two-hundred and twenty four diarrheic and 84 non-diarrheic stool specimens were collected from the Baqiyatallah hospital of Tehran, Iran. The stool samples were cultured immediately and those that were E. coli-positive were analyzed for the presence of antibiotic resistance genes and bacterial virulence factors using PCR. Antimicrobial susceptibility testing was performed using disk diffusion method.

Results

One-hundred and fifty four out of 224 (68.75%) diarrheic stools and 31 out of 84 (36.90%) non-diarrheic stools harbored E. coli. In addition, children in 13–24 month-old age group had the highest incidence of infection with this bacterium (77.63%). A significant difference was found between the frequency of Attaching and Effacing Escherichia coli and Enterohaemorrhagic Escherichia coli (P =0.045). The genes encoding Shiga toxins and intimin were the most commonly detected virulence factors. Among all serogroups studied, O26 (27.04%) and O111 (18.85%) had the highest incidences in the diarrheic and non-diarrheic patients. The incidence of genes encoding resistance against sulfonamide (sul1), gentamicin (aac(3)-IV), trimethoprim (aadA1), cephalothin (blaSHV) and tetracycline (tetA) were 82.78%, 68.03%, 60.65%, 56.55% and 51.63%, respectively. High resistance levels against penicillin (100%), tetracycline (86.88%), gentamicin (62.29%) and streptomycin (54.91%) were observed. Marked seasonality in the serogroup distributions was evident, while STEC infections were more common in summer (P =0.041).

Conclusions

Our findings should raise awareness about antibiotic resistance in diarrheic pediatric patients in Iran. Clinicians should exercise caution when prescribing antibiotics, especially during the warmer months of the year.

Molecular and phenotypic characterization of Escherichia coli O26:H8 among diarrheagenic E. coli O26 strains isolated in Brazil

Escherichia coli strains of serogroup O26 comprise two distinct groups of pathogens, characterized as enteropathogenic E. coli (EPEC) and enterohemorrhagic E. coli (EHEC). Among the several genes related to type III secretion system-secreted effector proteins, espK was found to be highly specific for EHEC O26:H11 and its stx-negative derivative strains isolated in European countries. E. coli O26 strains isolated in Brazil from infant diarrhea, foods, and the environment have consistently been shown to lack stx genes and are thus considered atypical EPEC. However, no further information related to their genetic background is known. Therefore, in this study, we aimed to discriminate and characterize these Brazilian O26 stx-negative strains by phenotypic, genetic, and biochemical approaches. Among 44 isolates confirmed to be O26 isolates, most displayed flagellar antigen H11 or H32. Out of the 13 nonmotile isolates, 2 tested positive for fliCH11, and 11 were fliCH8 positive. The identification of genetic markers showed that several O26:H11 and all O26:H8 strains tested positive for espK and could therefore be discriminated as EHEC derivatives. The presence of H8 among EHEC O26 and its stx-negative derivative isolates is described for the first time. The interaction of three isolates with polarized Caco-2 cells and with intestinal biopsy specimen fragments ex vivo confirmed the ability of the O26 strains analyzed to cause attaching-and-effacing (A/E) lesions. The O26:H32 strains, isolated mostly from meat, were considered nonvirulent. Knowledge of the virulence content of stx-negative O26 isolates within the same serotype helped to avoid misclassification of isolates, which certainly has important implications for public health surveillance.

Genome Sequence of Porcine Escherichia coli Strain IMT8073, an Atypical Enteropathogenic E. coli Strain Isolated from a Piglet with Diarrhea

Escherichia coli is a highly diverse bacterial species, with atypical enteropathogenic E. coli (aEPEC) causing intestinal disease in both human and animal hosts. Here, we report the first complete genome sequence of an aEPEC strain of sequence type ST794 and serotype Ont:H7, isolated from a diseased piglet.

Differences in virulence gene expression between atypical enteropathogenic Escherichia coli strains isolated from diarrheic and healthy ruminants

Differences in the pathogenicity of atypical enteropathogenic Escherichia coli (EPEC) strains may be due, at least partially, to different expression patterns of some virulence genes. To investigate this hypothesis, the virulence gene expression patterns of 6 atypical EPEC strains isolated from healthy and diarrheic ruminants were compared using quantitative real-time reverse transcription polymerase chain reaction after growing the bacteria in culture medium alone or after binding it to HeLa epithelial cells. Some virulence genes in strains from diarrheic animals were upregulated relative to their expression in strains from healthy animals. When bacteria were cultured in the presence of HeLa cells, the ehxA and efa1/lifA genes, previously associated with the production of diarrhea, were expressed at higher levels in strains from diarrheic animals than in strains from healthy animals. Thus, the expression levels of some virulence genes may help determine which atypical EPEC strains cause diarrhea in ruminants.

Low-molecular mass comparative proteome of four atypical enteropathogenic Escherichia coli isolates showing different adherence patterns

Atypical enteropathogenic Escherichia coli (aEPEC) are heterogeneous in terms of serotypes, adherence patterns and the presence of non-locus of enterocyte effacement virulence factors. In this study, the low-molecular mass proteomes of four representative aEPEC, comprising three different adhesion phenotypes (localized-like, aggregative and diffuse) and one non-adherent isolate, were analyzed and compared by 2D gel electrophoresis and LC-MS/MS. By mass spectrometry, a total of 59 proteins were identified according to their annotated function, with most of them being involved in metabolism, protection, and transport; some of them still classified as hypothetical proteins. Thus, in this comparative proteomic analysis of low-molecular mass extracted proteins from different aEPEC isolates, the proteins identified are mainly involved in key metabolic pathways. Also, the majority of the hypothetical and filamentous proteins identified in the isolates studied are products of genes originally identified in the genome of enterohemorrhagic E. coli.

Enteropathogenic escherichia coli infection in children

PURPOSE OF REVIEW

Enteropathogenic Escherichia coli (EPEC) is an important diarrheal pathogen of young children. As the diagnosis of EPEC is now based mainly on molecular criteria, there has been an important change in its prevalence. The purpose of this study is to review the current epidemiology of EPEC infection and the new insights into its physiopathology.

RECENT FINDINGS

Recent epidemiological studies indicate that atypical EPEC (aEPEC) is more prevalent than typical EPEC (tEPEC) in both developed and developing countries, and that aEPEC is important in both pediatric endemic diarrhea and diarrhea outbreaks. Therefore, it is important to further characterize the pathogenicity of these emerging strains. The virulence mechanisms and physiopathology of the attaching and effacing lesion (A/E) and the type three secretion-system (T3SS) are complex but well studied. A/E strains use their pool of locus of enterocyte effacement (LEE)-encoded and non-LEE-encoded effector proteins to subvert and modulate cellular and barrier properties of the host. However, the exact mechanisms of diarrhea in EPEC infection are not completely understood.

SUMMARY

Remarkable progress has been made to identify virulence determinants required to mediate the pathogenesis of EPEC. However, fast, easy, and inexpensive diagnostic methods are needed in order to define optimal treatment and prevention for children in endemic areas.

The ability of haemolysins expressed by atypical enteropathogenic Escherichia coli to bind to extracellular matrix components

Typical and atypical enteropathogenic Escherichia coli (EPEC) are considered important bacterial causes of diarrhoea. Considering the repertoire of virulence genes, atypical EPEC (aEPEC) is a heterogeneous group, harbouring genes that are found in other diarrheagenic E. coli pathotypes, such as those encoding haemolysins. Haemolysins are cytolytic toxins that lyse host cells disrupting the function of the plasma membrane. In addition, these cytolysins mediate a connection to vascular tissue and/or blood components, such as plasma and cellular fibronectin. Therefore, we investigated the haemolytic activity of 72 aEPEC isolates and determined the correlation of this phenotype with the presence of genes encoding enterohaemolysins (Ehly) and cytolysin A (ClyA). In addition, the correlation between the expression of haemolysins and the ability of these secreted proteins to adhere to extracellular matrix (ECM) components was also assessed in this study. Our findings demonstrate that a subset of aEPEC presents haemolytic activity due to the expression of Ehlys and/or ClyA and that this activity is closely related to the ability of these isolates to bind to ECM components.

Adhesin-encoding genes from shiga toxin-producing Escherichia coli are more prevalent in atypical than in typical enteropathogenic E. coli

Four of six adhesin-encoding genes (lpfA, paa, iha, and toxB) from Shiga toxin-producing Escherichia coli strains were detected in typical and atypical enteropathogenic E. coli (EPEC) strains of various serotypes. Although the most prevalent gene was lpfA in both groups, paa was the only potential diarrhea-associated gene in atypical EPEC.

Distribution of non-locus of enterocyte effacement pathogenic island-related genes in Escherichia coli carrying eae from patients with diarrhea and healthy individuals in Japan

The relationship to diarrhea of genes located on the pathogenicity islands (PAI) other than the locus of enterocyte effacement (LEE) was investigated. Enteropathogenic Escherichia coli (EPEC), the retention of espC on the EspC PAI, the OI-122 genes (efa1/lifA, nleB), the phylogenetic marker gene yjaA, and the bundle-forming pilus gene bfpA on the EPEC adherence factor (EAF) plasmid were studied. E. coli strains carrying the intimin gene (eae) without the Shiga toxin gene, isolated from patients with diarrhea (n = 83) and healthy individuals (n = 38) in Japan, were evaluated using PCR. The genotypes of eae and espC were identified by heteroduplex mobility assay (HMA). The proportions of strains isolated from individuals with and without diarrhea that carried these genes were as follows: bfpA, 13.3 and 7.9%, respectively; espC, 25.3 and 36.8%; efa1/lifA, 32.5 and 13.2%; nleB, 63.9 and 60.5%; yjaA, 42.2 and 55.3%. Statistical significance (P < 0.05) was achieved only for efa1/lifA. The proportion of strains lacking espC and carrying efa1/lifA was higher for patient-derived strains (30.1%) than for strains from healthy individuals (13.2%), but the difference was not significant. Strains carrying both espC and efa1/lifA were rare (2 strains from patients). Statistical analyses revealed significant relationships between espC and yjaA and between efa1/lifA and nleB, as well as significant inverse relationships between espC and efa1/lifA and between efa1/lifA and yjaA. espC was found in eae HMA types a1, a2, and c2, whereas efa1/lifA was found in types b1, b2, and c1. In addition, 6 polymorphisms of espC were found. The espC, yjaA, efa1/lifA, and nleB genes were mutually dependent, and their distributions were related to eae type, findings that should be considered in future epidemiological studies.

Prevalence and characteristics of the O122 pathogenicity island in typical and atypical enteropathogenic Escherichia coli strains

The presence of the pathogenicity island (PAI) O122 genes, efa1 (lifA), sen, pagC, nleB, and nleE, in typical and atypical enteropathogenic Escherichia coli (EPEC) strains was investigated. The simultaneous occurrence of all genes was statistically associated with diarrhea due to atypical EPEC. Detection of the complete PAI O122 could aid in the identification of potential pathogenic strains of atypical EPEC.

Adherence factors in atypical enteropathogenic Escherichia coli strains expressing the localized adherence-like pattern in HEp-2 cells

Although atypical enteropathogenic Escherichia coli (aEPEC) strains are frequently implicated in childhood diarrhea in developing countries, not much is known about their adherence properties. The phenotypic and genotypic characterization of 29 aEPEC strains expressing the localized adherence-like pattern points toward the involvement of E. coli common pilus (ECP), intimins, and other known E. coli adhesins in this pattern.