Distribution and expression of the astA gene (EAST1 toxin) in Escherichia coli and Salmonella

Pathogenic profile and antimicrobial resistance of Escherichia coli, Escherichia marmotae and Escherichia ruysiae detected from hunted wild boars in Sardinia (Italy)

The objective of this study was to evaluate the occurrence of E. coli in hunted wild boars in Sardinia (Italy) and to further characterize the isolates with Whole Genome Sequencing to assess the genetic relatedness and the presence of virulence and antimicrobial resistance (AMR) genes. Samples were taken from 66 wild boars between 2020 and 2022 slaughtered in five hunting houses. A total of 181 samples were tested, including 66 samples from mesenteric lymph nodes, 66 samples from colon content and 49 samples from carcass surface. Isolates referable to Escherichia species were detected in all of the wild boars sampled. On a selection of 61 isolates, sequencing was conducted and antimicrobial susceptibility was tested. Among these, three isolates were confirmed to be two Escherichia marmotae (cryptic clade V) and one Escherichia ruysiae (cryptic clade III). E. coli pathotypes identified were UPEC (13 %), ExPEC-UPEC (5.6 %) and ETEC (3.7 %). Moreover, 3/6 E. marmotae isolates had typical ExPEC genes. Genetic similarity was observed in isolates collected from animals slaughtered in the same hunting house; this suggests epidemiological links deriving from the presence of animals infected with closely related strains or the result of cross-contamination. Antimicrobial resistance genes were detected in three non-pathogenic E. coli isolates: one isolate had sul2, tet(B), aph(6)-ld and aph(3″)-lb resistance genes and two had the fosA7 gene. This study confirmed that wild boars can act as reservoirs and spreaders of pathogenic Escherichia species and it provides information for future comparative genomic analysis in wildlife. Although isolates showed a limited resistome, the detection of resistance in non-pathogenic isolates underlines the need to monitor antimicrobial resistance in the wild boar population. To the best of our knowledge, this is the first detection of E. mamotae and E. ruysiae isolates in wild boars in Italy and the presence of this pathogen in wildlife and livestock need to be investigated further.

A statistical approach to identify prevalent virulence factors responsible for post-weaning diarrhoeic piglets

A statistical approach was carried out to identify the prevalent virulence factors responsible for post-weaning diarrhoea (PWD). Healthy piglets' faecal samples and diarrhoeic piglets' rectal swab specimens were secured. Twenty-six (26) and 100 independent enterotoxigenic Escherichia coli (ETEC) strains were subsequently isolated. These strains were assessed utilising polymerase chain reaction to identify the encoding genes of six virulence factors: heat-labile enterotoxin (LT; encoded by eltAB), heat-stable enterotoxin A (STa; encoded by estA), heat-stable enterotoxin B (STb; encoded by estB), enteroaggregative E. coli heat-stable enterotoxin 1 (EAST1; encoded by astA), Shiga toxin 2e (Stx2e; encoded by stx2e), and F18 fimbriae (encoded by fedA). The LT and ST secretions were investigated using enzyme-linked immunosorbent assays. From direct observation, no stx2e was evident in the 126 strains. Among the 26 strains retrieved from the healthy piglets, none harboured fedA or secreted LT; 23% (6/26) secreted ST, and 50% (13/26) carried astA. A statistical regression was applied on the 100 E. coli strains retrieved from the diarrhoeic piglets, where fedA was set as the dependent variable and the enterotoxin secretions were set as the independent variables. The results exhibit that the LT secretion was the only significant factor (P < 0.000 1) correlated to fedA in the diarrhoeic piglets; thus, it is concluded that the prevalent virulence factors for PWD were the ECET strain with F18 fimbriae adhesion and LT secretion, but not astA or stx2e.

An Integrated Perspective on Virulence-Associated Genes (VAGs), Antimicrobial Resistance (AMR), and Phylogenetic Clusters of Pathogenic and Non-pathogenic Avian Escherichia coli

Avian pathogenic Escherichia coli (APEC) is an important bacterial pathogen that causes avian colibacillosis and leads to huge economic losses in the poultry industry. Different virulence traits contribute to pathogenesis of APEC infections, and antimicrobial resistance (AMR) has also been an overwhelming issue in poultry worldwide. In the present study, we aimed to investigate and compare the presence of virulence-associated genes (VAGs), AMR, and phylogenetic group's distribution among APEC and avian fecal E. coli (AFEC) strains. E. coli from birds with colisepticemia and yolk sac infection (YSI) (APEC) plus E. coli strains from the feces of healthy birds (AFEC) were compared by the aforementioned traits. In addition, the clonal relatedness was compared using Enterobacterial repetitive intergenic consensus PCR (ERIC-PCR). Although all strains were susceptible to fosfomycin, ceftriaxone, and cefixime, almost all strains (98%) were multi-drug resistant (MDR). All strains (except two) harbored at least three or more VAGs, and the virulence scores tended to be higher in pathogenic strains especially in the colisepticemic group. All phylogenetic groups were found in isolates from YSI, colisepticemia, and the feces of healthy birds; however, the frequency of phylogroups varied according to the source of the isolate. B1 and C phylogroups were statistically more likely to be found among APEC from YSI and colisepticemic E. coli groups, respectively, while phylogroup A was the most frequently occurring phylogroup among AFEC strains. Our findings also revealed that AMR and VAGs are not essentially co-evolved traits as in some instances AMR strains were more prevalent among AFEC. This reflects the divergent evolutionary pathways of resistance acquisition in pathogenic or non-pathogenic avian E. coli strains. Importantly, strains related to phylogenetic group C showed higher virulence score and AMR that requires further attention. To some extent, ERIC-PCR was able to group strains by isolation source, phylogroup, or virulence genes. Further integrated studies along with assessment of more detailed genotypic and phenotypic features could potentially lead to better understanding of virulence, resistance, and evolution of ExPEC.

Genomic Surveillance of Ceftriaxone-Resistant Escherichia coli in Western New York Suggests the Extended-Spectrum β-Lactamase bla CTX-M-27 Is Emerging on Distinct Plasmids in ST38

Extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae pose significant treatment and infection prevention challenges. Escherichia coli sequence type (ST) 131 associated with the bla_CTX-M-15 gene has been the dominant lineage of ESBL-producing E. coli in the US and worldwide. In this study, our objective was to determine the β-lactamase profile, means of dissemination, prevalence, and the clonal identity of ESBL-producing E. coli in our region of Western New York. Whole-genome SNP-based phylogenomics was used to assess 89 ceftriaxone-resistant (CTR) E. coli. Isolates were collected from both inpatients and outpatients and from urine and sterile-sites over a 2 month period in 2017 or throughout the year, respectively. ST131 was the predominant ST (46.0%), followed by ST38 (15.7%). The bla_CTX-M-15 gene was commonly found in 53.7% of ST131 isolates, whereas the bla_CTX-M-27 gene was found in 26.8% of ST131, though was significantly associated with ST38, and was found in 71.4% of those strains. When compared to ST131, ST38 E. coli exhibited increased frequency of resistance to nitrofurantoin and decreased frequency of resistance to ciprofloxacin and ampicillin-sulbactam. Using Nanopore long-read sequencing technology, an analysis of the ESBL genetic context showed that the bla_CTX-M-15 gene was chromosomal in 68.2% of ST131, whereas the bla_CTX-M-27 gene was plasmid-borne in all ST131 and 90% of ST38 isolates. Notably, the bla_CTX-M-27 gene in ST38 resided on highly-related (99.0–100.0% identity and 65.0–98.0% query coverage) conjugative IncF plasmids of distinct plasmid multi-locus sequence types (pMLSTs) from those in ST131. Furthermore, ST131 and ST38 were found to harbor different antibiotic resistance gene and virulence factor profiles. These findings raise the possibility of an emerging ESBL-producing E. coli lineage in our region.

Prevalence of Colistin Resistance in Escherichia coli in Eastern Turkey and Genomic Characterization of an mcr-1 Positive Strain from Retail Chicken Meat

Colistin is one of the most effective antibiotics against multidrug resistant Gram-negative bacteria. However, the recent emergence of plasmid-borne mobilized colistin resistance (mcr) genes is considered a serious antimicrobial resistance challenge worldwide. In this study, we report detection of an mcr-1 carrying Escherichia coli isolate (named ATAVET mcr-1 Turkey) from retail raw chicken meat in Turkey. Of the 11 (from 500 total tested) phenotypically colistin-resistant isolates, 1 was shown to carry the mcr-1 gene by PCR. Whole-genome sequencing indicated that mcr-1 was located on a ∼13 kb-long contig that was almost identical to the corresponding part in pZJ1635, an IncI2 plasmid encoding mcr-1 in the same genetic context in another E. coli strain. In addition, ATAVET mcr-1 Turkey harbored bla_CTX-M-8, qnrB19, mdf(A), tet(A), sul2, aph(3″)-Ib, aph(6)-Id, and floR resistance genes. Phylogenetic analysis based on whole genome and multilocus sequence typing indicated that ATAVET mcr-1 Turkey was more closely related to mcr-1 carrying E. coli isolates from food and human clinical samples previously reported from different parts of the world than to those from Turkey. These findings further emphasize the worldwide emergence and spread of mcr meditated colistin resistance in bacteria with zoonotic potential within animals and the food chain.

An Extended-Spectrum Beta-Lactamase-Producing Hybrid Shiga-Toxigenic and Enterotoxigenic Escherichia coli Strain Isolated from a Piglet with Diarrheal Disease in Northeast China

Shiga-toxigenic Escherichia coli (STEC) and enterotoxigenic E. coli (ETEC) can cause diarrhea in piglets. This is the first report and complete genome sequence of an extended-spectrum β-lactamase-producing hybrid STEC/ETEC strain isolated from a piglet with diarrhea on a swine farm in China. We investigated the virulence genes and phylogenetic diversity with publicly available E. coli genomes. Both E. coli strains S17-13 and S17-20 harbored multiple virulence genes, mainly including stx2e and eastA genes. Other important virulence genes (estIa, estIb, fedABCDEF, and hlyABCD) were located in the plasmid p1713-1 of S17-13, which could be transferred from E. coli S17-13 to S17-20 by conjugation. The presence of virulence genes associated with different pathogroups (STEC or ETEC) confirmed the hybrid status of E. coli strain S17-13. Phylogenetic analysis showed that STEC/ETEC S17-13, STEC S17-20, avian pathogenic E. coli (APEC) O78, and APEC ACN001 are located in the same evolutionary branch, indicating that they may originate from a common ancestor. It is crucial to understand the phylogeny of pathogenic bacteria to evaluate how they have evolved and to monitor the emergence of potential new pathogens. The emergence of novel hybrid E. coli strains presents a new public health risk. More attention must be paid to these hybrid pathogens during typing and epidemiological surveillance of E. coli infections, which challenges the traditional diagnostics of E. coli infections.

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.

Molecular Characterization and Comparative Genomics of Clinical Hybrid Shiga Toxin-Producing and Enterotoxigenic Escherichia coli (STEC/ETEC) Strains in Sweden

Hybrid E. coli pathotypes are representing emerging public health threats with enhanced virulence from different pathotypes. Hybrids of Shiga toxin-producing and enterotoxigenic E. coli (STEC/ETEC) have been reported to be associated with diarrheal disease and hemolytic uremic syndrome (HUS) in humans. Here, we identified and characterized four clinical STEC/ETEC hybrids from diarrheal patients with or without fever or abdominal pain and healthy contact in Sweden. Rare stx2 subtypes were present in STEC/ETEC hybrids. Stx2 production was detectable in stx2a and stx2e containing strains. Different copies of ETEC virulence marker, sta gene, were found in two hybrids. Three sta subtypes, namely, sta1, sta4 and sta5 were designated, with sta4 being predominant. The hybrids represented diverse and rare serotypes (O15:H16, O187:H28, O100:H30, and O136:H12). Genome-wide phylogeny revealed that these hybrids exhibited close relatedness with certain ETEC, STEC/ETEC hybrid and commensal E. coli strains, implying the potential acquisition of Stx-phages or/and ETEC virulence genes in the emergence of STEC/ETEC hybrids. Given the emergence and public health significance of hybrid pathotypes, a broader range of virulence markers should be considered in the E. coli pathotypes diagnostics, and targeted follow up of cases is suggested to better understand the hybrid infection.

Identification of Subsets of Enteroaggregative Escherichia coli Associated with Diarrheal Disease among Under 5 Years of Age Children from Rural Gambia

Enteroaggregative Escherichia coli (EAEC) cause acute and persistent diarrhea, mostly in children worldwide. Outbreaks of diarrhea caused by EAEC have been described, including a large outbreak caused by a Shiga toxin expressing strain. This study investigated the association of EAEC virulence factors with diarrhea in children less than 5 years. We characterized 428 EAEC strains isolated from stool samples obtained from moderate-to-severe diarrhea cases (157) and healthy controls (217) children aged 0–59 months recruited over 3 years as part of the Global Enteric Multicenter Study (GEMS) in The Gambia. Four sets of multiplex polymerase chain reaction were applied to detect 21 EAEC-virulence genes from confirmed EAEC strains that target pCVD432 (aatA) and AAIC (aaiC). In addition, Kirby-Bauer disc diffusion antimicrobial susceptibility testing was performed on 88 EAEC strains following Clinical Laboratory Standard Institute guidelines. We observed that the plasmid-encoded enterotoxin [odds ratio (OR): 6.9, 95% confidence interval (CI): 2.06–29.20, P < 0.001], aggregative adherence fimbriae/I fimbriae (aggA) [OR: 2.2, 95% CI: 1.16–4.29, P = 0.008], and hexosyltransferase (capU) [OR: 1.9, 95% CI 1.02–3.51, P = 0.028] were associated with moderate-to-severe diarrhea among children < 12 months old but not in the older age strata (> 12 months). Our data suggest that some EAEC-virulent factors have age-specific associations with moderate-to-severe diarrhea in infants. Furthermore, our study showed that 85% and 72% of EAEC strains tested were resistant to sulphamethoxazole-trimethoprim and ampicillin, respectively. Sulphamethoxazole-trimethoprim and ampicillin are among the first-line antibiotics used for the treatment of diarrhea in The Gambia.

Characterization and Virulence Potential of Serogroup O113 Shiga Toxin-Producing Escherichia coli Strains Isolated from Beef and Cattle in the United States

Shiga toxin-producing Escherichia coli (STEC) of serotype O113:H21 have caused severe diseases but are unusual in that they do not produce the intimin protein required for adherence to intestinal epithelial cells. Strains of serogroup O113 are one of the most common STEC found in ground beef and beef products in the United States, but their virulence potential is unknown. We used a microarray to characterize 65 O113 strains isolated in the United States from ground beef, beef trim, cattle feces, and fresh spinach. Most were O113:H21 strains, but there were also nine strains of O113:H4 serotype. Although strains within the same serotype had similar profiles for the genes that were tested on the array, the profiles were distinct between the two serotypes, and the strains belonged to different clonal groups. Analysis by clustered regularly interspaced short palindromic repeat analysis showed that O113:H4 strains are conserved genetically, but the O113:H21 strains showed considerable polymorphism and genetic diversity. In comparison to the O113:H21 strains from Australia that were implicated in severe disease, the U.S. isolates showed similar genetic profiles to the known pathogens from Australia, suggesting that these may also have the potential to cause infections.

Animal Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is the most common cause of E. coli diarrhea in farm animals. ETEC are characterized by the ability to produce two types of virulence factors: adhesins that promote binding to specific enterocyte receptors for intestinal colonization and enterotoxins responsible for fluid secretion. The best-characterized adhesins are expressed in the context of fimbriae, such as the F4 (also designated K88), F5 (K99), F6 (987P), F17, and F18 fimbriae. Once established in the animal small intestine, ETEC produce enterotoxin(s) that lead to diarrhea. The enterotoxins belong to two major classes: heat-labile toxins that consist of one active and five binding subunits (LT), and heat-stable toxins that are small polypeptides (STa, STb, and EAST1). This review describes the disease and pathogenesis of animal ETEC, the corresponding virulence genes and protein products of these bacteria, their regulation and targets in animal hosts, as well as mechanisms of action. Furthermore, vaccines, inhibitors, probiotics, and the identification of potential new targets by genomics are presented in the context of animal ETEC.

Detection and risk assessment of diarrheagenic E. coli in recreational beaches of Brazil

Marine beaches are important recreational and economic resources in Brazil, but the beaches' water quality is negatively impacted by the discharge of domestic sewage effluent. The occurrence of diarrheagenic Escherichiacoli among the E. coli isolated from three Brazilian marine beaches was investigated. Multiplex and single step PCR were used to screen 99 E. coli isolates for ten target toxin genes. Six toxin genes, stx1, eae, estp, esth, astA, and bfpA, were identified in 1% to 35% of the isolates. A quantitative microbial risk assessment (QMRA) of human exposure to diarrheagenic E. coli during marine recreation was carried out. The results indicated that the diarrheagenic E. coli risk is well below the U.S. EPA's recommended daily recreational risk benchmark. However, the overall recreational health risk due to all pathogens in the water could be much higher and exceeded the U.S. EPA's benchmark.

Comparative Genomics and Characterization of Hybrid Shigatoxigenic and Enterotoxigenic Escherichia coli (STEC/ETEC) Strains

Background

Shigatoxigenic Escherichia coli (STEC) and enterotoxigenic E. coli (ETEC) cause serious foodborne infections in humans. These two pathogroups are defined based on the pathogroup-associated virulence genes: stx encoding Shiga toxin (Stx) for STEC and elt encoding heat-labile and/or est encoding heat-stable enterotoxin (ST) for ETEC. The study investigated the genomics of STEC/ETEC hybrid strains to determine their phylogenetic position among E. coli and to define the virulence genes they harbor.

Methods

The whole genomes of three STEC/ETEC strains possessing both stx and est genes were sequenced using PacBio RS sequencer. Two of the strains were isolated from the patients, one with hemolytic uremic syndrome, and one with diarrhea. The third strain was of bovine origin. Core genome analysis of the shared chromosomal genes and comparison with E. coli and Shigella spp. reference genomes was performed to determine the phylogenetic position of the STEC/ETEC strains. In addition, a set of virulence genes and ETEC colonization factors were extracted from the genomes. The production of Stx and ST were studied.

Results

The human STEC/ETEC strains clustered with strains representing ETEC, STEC, enteroaggregative E. coli, and commensal and laboratory-adapted E. coli. However, the bovine STEC/ETEC strain formed a remote cluster with two STECs of bovine origin. All three STEC/ETEC strains harbored several other virulence genes, apart from stx and est, and lacked ETEC colonization factors. Two STEC/ETEC strains produced both toxins and one strain Stx only.

Conclusions

This study shows that pathogroup-associated virulence genes of different E. coli can co-exist in strains originating from different phylogenetic lineages. The possibility of virulence genes to be associated with several E. coli pathogroups should be taken into account in strain typing and in epidemiological surveillance. Development of novel hybrid E. coli strains may cause a new public health risk, which challenges the traditional diagnostics of E. coli infections.

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.

Hybrids of Shigatoxigenic and Enterotoxigenic Escherichia coli (STEC/ETEC) Among Human and Animal Isolates in Finland

Diarrhoeagenic Escherichia coli (DEC) cause serious foodborne infections in humans. Total of 450 Shigatoxigenic E. coli (STEC) strains isolated from humans, animals and environment in Finland were examined by multiplex PCR targeting the virulence genes of various DEC pathogroups simultaneously. One per cent (3/291) of the human STEC and 14% (22/159) of the animal and environmental STEC had genes typically present in enterotoxigenic E. coli (ETEC). The strains possessed genes encoding both Shiga toxin 1 and/or 2 (stx1 and/or stx2 ) and ETEC-specific heat-stable (ST) enterotoxin Ia (estIa). The identified stx subtypes were stx1a, stx1c, stx2a, stx2d and stx2g. The three human STEC/ETEC strains were isolated from the patients with haemolytic uraemic syndrome and diarrhoea and from an asymptomatic carrier. The animal STEC/ETEC strains were isolated from cattle and moose. The human and animal STEC/ETEC strains belonged to 11 serotypes, of which O2:H27, O15:H16, O101:H-, O128:H8 and O141:H8 have previously been described to be associated with human disease. Identification of multiple virulence genes offers further information for assessing the virulence potential of STEC and other DEC. The emergence of novel hybrid pathogens should be taken into account in the patient care and epidemiological surveillance.

Escherichia coli STb enterotoxin dislodges claudin-1 from epithelial tight junctions

Enterotoxigenic Escherichia coli produce various heat-labile and heat-stable enterotoxins. STb is a low molecular weight heat-resistant toxin responsible for diarrhea in farm animals, mainly young pigs. A previous study demonstrated that cells having internalized STb toxin induce epithelial barrier dysfunction through changes in tight junction (TJ) proteins. These modifications contribute probably to the diarrhea observed. To gain insight into the mechanism of increased intestinal permeability following STb exposure we treated human colon cells (T84) with purified STb toxin after which cells were harvested and proteins extracted. Using a 1% Nonidet P-40-containing solution we investigated the distribution of claudin-1, a major structural and functional TJ protein responsible for the epithelium impermeability, between membrane (NP40-insoluble) and the cytoplasmic (NP-40 soluble) location. Using immunoblot and confocal microscopy, we observed that treatment of T84 cell monolayers with STb induced redistribution of claudin-1. After 24 h, cells grown in Ca⁺⁺-free medium treated with STb showed about 40% more claudin-1 in the cytoplasm compare to the control. Switching from Ca⁺⁺-free to Ca⁺⁺-enriched medium (1.8 mM) increased the dislodgement rate of claudin-1 as comparable quantitative delocalization was observed after only 6 h. Medium supplemented with the same concentration of Mg⁺⁺ or Zn⁺⁺ did not affect the dislodgement rate compared to the Ca⁺⁺-free medium. Using anti-phosphoserine and anti-phosphothreonine antibodies, we observed that the loss of membrane claudin-1 was accompanied by dephosphorylation of this TJ protein. Overall, our findings showed an important redistribution of claudin-1 in cells treated with STb toxin. The loss of phosphorylated TJ membrane claudin-1 is likely to be involved in the increased permeability observed. The mechanisms by which these changes are brought about remain to be elucidated.

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.

Genetic diversity and virulence potential of shiga toxin-producing Escherichia coli O113:H21 strains isolated from clinical, environmental, and food sources

Shiga toxin-producing Escherichia coli strains of serotype O113:H21 have caused severe human diseases, but they are unusual in that they do not produce adherence factors coded by the locus of enterocyte effacement. Here, a PCR microarray was used to characterize 65 O113:H21 strains isolated from the environment, food, and clinical infections from various countries. In comparison to the pathogenic strains that were implicated in hemolytic-uremic syndrome in Australia, there were no clear differences between the pathogens and the environmental strains with respect to the 41 genetic markers tested. Furthermore, all of the strains carried only Shiga toxin subtypes associated with human infections, suggesting that the environmental strains have the potential to cause disease. Most of the O113:H21 strains were closely related and belonged in the same clonal group (ST-223), but CRISPR analysis showed a great degree of genetic diversity among the O113:H21 strains.

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.

Escherichia coli expressing EAST1 toxin did not cause an increase of cAMP or cGMP levels in cells, and no diarrhea in 5-day old gnotobiotic pigs

Background

Enterotoxigenic Escherichia coli (ETEC) strains are the leading bacterial cause of diarrhea to humans and farm animals. These ETEC strains produce heat-labile toxin (LT) and/or heat-stable toxins that include type I (STa), type II (STb), and enteroaggregative heat-stable toxin 1 (EAST1). LT, STa, and STb (in pigs) are proven the virulence determinants in ETEC diarrhea. However, significance of EAST1 in ETEC-associated diarrheal has not been determined, even though EAST1 is highly prevalent among ETEC strains.

Methodology/Principal Findings

In this study, we constructed E. coli strains to express EAST1 toxin as the only toxin and studied them in cell lines and five-day old gnotobiotic piglets to determine significance of EAST1 toxin. Data from in vitro studies indicated that EAST1 did not stimulate an increase of intracellular cyclic AMP or GMP levels in T-84 cells or porcine cell line IPEC-J2, nor did it enhance LT or STa toxin of ETEC strains in stimulation of cAMP or cGMP in T-84 cells. In addition, 5-day old gnotobiotic pigs challenged with E. coli strains expressing EAST1 as the only toxin did not developed diarrhea or signs of clinical disease during 72 h post-inoculation.

Conclusion/Significance

Results from this study indicated that EAST1 alone is not sufficient to cause diarrhea in five-day old gnotobiotic pigs, and suggest that EAST1 likely is not a virulence determinant in ETEC-associated diarrhea.

Molecular characterization of diarrheagenic Escherichia coli from Libya

Diarrheagenic Escherichia coli (DEC) are important enteric pathogens that cause a wide variety of gastrointestinal diseases, particularly in children. Escherichia coli isolates cultured from 243 diarrheal stool samples obtained from Libyan children and 50 water samples were screened by polymerase chain reaction (PCR) for genes characteristic of enteroaggregative E. coli (EAEC), enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), enterohemorrhagic E. coli (EHEC), and enteroinvasive E. coli (EIEC). The DEC were detected in 21 (8.6%) children with diarrhea; 10 (4.1%) cases were identified as EAEC, 3 (1.2%) as EPEC, and 8 (3.3%) were ETEC; EHEC, and EIEC were not detected. All DEC were grouped phylogenetically by PCR with the majority (> 70%) identified as phylogenetic groups A and B1. The EAEC isolates were also tested for eight genes associated with virulence using PCR. Multi-virulence (≥ 3 virulence factors) was found in 50% of EAEC isolates. Isolated EAEC possessed different virulence traits and belonged to different phylogenetic groups indicating their heterogeneity.

Phylogenetic grouping and virulence potential of extended-spectrum-β-lactamase-producing Escherichia coli strains in cattle

In line with recent reports of extended-spectrum beta-lactamases (ESBLs) in Escherichia coli isolates of highly virulent serotypes, such as O104:H4, we investigated the distribution of phylogroups (A, B1, B2, D) and virulence factor (VF)-encoding genes in 204 ESBL-producing E. coli isolates from diarrheic cattle. ESBL genes, VFs, and phylogroups were identified by PCR and a commercial DNA array (Alere, France). ESBL genes belonged mostly to the CTX-M-1 (65.7%) and CTX-M-9 (27.0%) groups, whereas those of the CTX-M-2 and TEM groups were much less represented (3.9% and 3.4%, respectively). One ESBL isolate was stx(1) and eae positive and belonged to a major enterohemorrhagic E. coli (EHEC) serotype (O111:H8). Two other isolates were eae positive but stx negative; one of these had serotype O26:H11. ESBL isolates belonged mainly to phylogroup A (55.4%) and, to lesser extents, to phylogroups D (25.5%) and B1 (15.6%), whereas B2 strains were quasi-absent (1/204). The number of VFs was significantly higher in phylogroup B1 than in phylogroups A (P = 0.04) and D (P = 0.02). Almost all of the VFs detected were found in CTX-M-1 isolates, whereas only 64.3% and 33.3% of them were found in CTX-M-9 and CTX-M-2 isolates, respectively. These results indicated that the widespread dissemination of the bla(CTX-M) genes within the E. coli population from cattle still spared the subpopulation of EHEC/Shiga-toxigenic E. coli (STEC) isolates. In contrast to other reports on non-ESBL-producing isolates from domestic animals, B1 was not the main phylogroup identified. However, B1 was found to be the most virulent phylogroup, suggesting host-specific distribution of virulence determinants among phylogenetic groups.

Characterization of Escherichia coli strains isolated from patients with diarrhea in Sao Paulo, Brazil: identification of intermediate virulence factor profiles by multiplex PCR

Intestinal pathogenic Escherichia coli is a major causative agent of severe diarrhea. In this study the prevalences of different pathotypes among 702 E. coli isolates from Brazilian patients with diarrhea were determined by multiplex PCR. Interestingly, most strains were enteroaggregative E. coli (EAEC) strains, followed by atypical EPEC (ATEC) strains. Classical enteropathogenic E. coli (EPEC) strains were not detected.

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.

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.

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.

Escherichia coli EAST1 toxin toxicity of variants 17-2 and O 42

EAST1 (EnteroAggregative heat-Stable Toxin 1) is a 4.1kDa toxin that was first detected in the enteroaggregative Escherichia coli (EAEC) strain 17-2 (O3:H2) isolated from the stools of a Chilean child with diarrhoea. Accordingly, EAST1 is thought to play a role in the pathogenicity of EAEC. The goal of this study was to obtain purified biologically active forms of two EAST1 variants (17-2 and O 42). Purified toxin samples were treated with protein disulfide isomerase (PDI) to ascertain the integrity of the disulfide bridges. Since EAST1 is often compared to STa (heat-Stable Toxin a), both purified EAST1 variants were tested for biological activity using the suckling mouse assay, the reference test for STa. A positive gut to body (G/B) weight ratio was not observed for any of the EAST1 preparations tested, although STa was active. Exposure of the purified toxins to T84 cell monolayers, an epithelial cell line derived from a human colon carcinoma, in modified Ussing flux chambers resulted in a rapidly attained and prolonged increase in short circuit current, a sensitive measure of net ion transport. Responses to 17-2 and O 42 variants were comparable in magnitude and inhibitable by bumetanide and DASU-02, indicating net anion secretion. The results demonstrate that EAST1 toxin stimulates anion secretion by T84 cell monolayers and it is sustained for the duration of toxin exposure.

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.

Detection of enteroaggregative Escherichia coli in faecal samples from patients in the community with diarrhoea

The aim of this study was to assess the usefulness of a multiplex PCR assay targeting the aat, aaiA and astA genes for the detection of typical and atypical enteroaggregative Escherichia coli (EAEC) in bacterial cultures from faecal samples from patients with community-acquired diarrhoea. The isolates harbouring these genes were also tested using the HEp-2 cell-adhesion assay to clarify their EAEC status. aat, aai or astA was found in E. coli faecal isolates from 39 (7.8 %) of 500 patients, and 20 of these strains adhered to HEp-2 cells in a pattern characteristic of EAEC. Eight isolates carrying the aai or astA gene but not the aat gene were shown to be HEp-2 cell test positive, although 12 strains with this genotype were HEp-2 cell test negative. Using the HEp-2 adhesion assay as the gold standard, the addition of primers detecting aaiA and astA to the aat PCR increased the number of EAEC isolates detected, but identified strains of E. coli that were not EAEC. The variety of genotypes exhibiting aggregative adherence highlights the problems associated with developing a molecular diagnostic test for EAEC. This PCR assay detects a variety of strains exhibiting characteristics of the EAEC group, making it a useful tool for identifying both typical and atypical EAEC.

Detection of the astA (EAST1) Gene in Attaching and Effacing Escherichia coli from Ruminants

A total of 206 attaching and effacing Escherichia coli strains from ruminants were analysed for the presence of the astA (EAST1) and bfpA genes. None of these strains was bfpA-positive. The percentage of enteropathogenic E. coli (EPEC) strains astA-positive found in healthy cattle (15.6%) suggests that this animal species may be a significant reservoir of atypical EPEC potentially pathogenic for humans.

Towards more virulent and antibiotic-resistantSalmonella?

Salmonella are well-known pathogens. Virulence determinants can be present on the chromosome, usually encoded on pathogenicity islands, or on plasmids and bacteriophages. Antibiotic resistance determinants usually are encoded on plasmids, but can also be present on the multidrug resistance region of Salmonella Genomic Island 1 (SGI1). Virulence plasmids show a remarkable diversity in the combination of virulence factors they encode, which appears to adapt them to specific hosts and the ability to cause gastroenteritidis or systemic disease. The appearance of plasmids with two replicons may help to extend the host range of these plasmids and thereby increase the virulence of previously non- or low pathogenic serovars. Antibiotic resistance among Salmonella is also increasing. This increase is not only in the percentage isolates resistant to a particular antibiotic, but also the development of resistance against newer antibiotics. The increased occurrence of integrons is particularly worrying. Integrons can harbour a varying set of antibiotic resistance encoding gene cassettes. Gene cassettes can be exchanged between integrons. Although the gene cassettes currently present in Salmonella integrons encode for older antibiotics (however, some still frequently used) gene cassettes encoding resistance against the newest antibiotics has been documented in Enterobacteriaceae. Furthermore, beta-lactamases with activity against broad-spectrum cephalosporins, which are often used in empiric therapy, have been found associated with integrons. So, empiric treatment of Salmonella infections becomes increasingly more difficult. The most worrisome finding is that virulence and resistance plasmids form cointegrates. These newly formed plasmids can be selected by antibiotic pressure and thereby for virulence factors. Taken together these trends may lead to more virulent and antibiotic-resistant Salmonella.

Transposition of the heat-stable toxin astA gene into a gifsy-2-related prophage of Salmonella enterica serovar Abortusovis

The horizontal transfer and acquisition of virulence genes via mobile genetic elements have been a major driving force in the evolution of Salmonella pathogenicity. Serovars of Salmonella enterica carry variable assortments of phage-encoded virulence genes, suggesting that temperate phages play a pivotal role in this process. Epidemic isolates of S. enterica serovar Typhimurium are consistently lysogenic for two lambdoid phages, Gifsy-1 and Gifsy-2, carrying known virulence genes. Other serovars of S. enterica, including serovars Dublin, Gallinarum, Enteritidis, and Hadar, carry distinct prophages with similarity to the Gifsy phages. In this study, we analyzed Gifsy-related loci from S. enterica serovar Abortusovis, a pathogen associated exclusively with ovine infection. A cryptic prophage, closely related to serovar Typhimurium phage Gifsy-2, was identified. This element, named Gifsy-2AO, was shown to contribute to serovar Abortusovis systemic infection in lambs. Sequence analysis of the prophage b region showed a large deletion which covers genes encoding phage tail fiber proteins and putative virulence factors, including type III secreted effector protein SseI (GtgB, SrfH). This deletion was identified in most of the serovar Abortusovis isolates tested and might be dependent on the replicative transposition of an adjacent insertion sequence, IS1414, previously identified in pathogenic Escherichia coli strains. IS1414 encodes heat-stable toxin EAST1 (astA) and showed multiple genomic copies in isolates of serovar Abortusovis. To our knowledge, this is the first evidence of intergeneric transfer of virulence genes via insertion sequence elements in Salmonella. The acquisition of IS1414 (EAST1) and its frequent transposition within the chromosome might improve the fitness of serovar Abortusovis within its narrow ecological niche.

Enteroaggregative Escherichia coli virulence factors are found to be associated with infantile diarrhea in Brazil

We have previously shown that enteroaggregative Escherichia coli (EAEC) is an important pathogen among Brazilian infants. Most EAEC strains harbor a plasmid (pAA) from which a DNA fragment has been used as a probe (EAEC probe). To better understand the characteristics of EAEC in Brazil, 109 strains carrying and lacking the EAEC probe sequence were tested for the presence of pAA plasmid-borne and chromosomal factors. Common virulence factors of probe-positive and probe-negative isolates included the presence of the Pet, EAST-1, Shf, Irp2, ShET1/Pic, and Hly virulence markers. The presence of AggR or one other virulence factor (AAF/I, AAF/II, AAF/III, or Aap) was predominantly identified only in probe-positive strains. In EAEC probe-positive strains, the virulence marker Aap was found significantly more frequently (P = 0.023) in isolates from children with diarrhea (22%) than in isolates from controls (3%). EAST-1 and Shf were the markers most frequently detected (61%) in EAEC probe-negative strains and were found to be significantly associated with diarrhea (P = 0.003 and P = 0.020, respectively). Furthermore, our data suggest that AggR can be used as an important genetic marker for EAEC probe-positive strains.

Expression, purification, and biochemical characterization of enteroaggregative Escherichia coli heat-stable enterotoxin 1

Enteroaggregative Escherichia coli (EAEC) heat-stable enterotoxin 1 (EAST1) is a 4.1k Da protein originally discovered in EAEC but known to be scattered in other diarrheagenic E. coli as well, possibly causing diarrhea in humans and animals. We report for the first time a method to express and purify EAST1 using the Glutathione S-transferase (GST) fusion system. The gst and astA genes were fused together on a pGEX-2T plasmid vector to produce a GST-EAST1 fusion protein. Using Glutathione Sepharose affinity chromatography and C(8) reverse phase high pressure liquid chromatography, EAST1 was purified to homogeneity with a yield of 0.29 mg/L of culture. The protein purified by this method was confirmed to be EAST1 by NH(2)-terminal sequencing and mass spectrometry. The molecular weight of EAST1 is 4104.0 Da, confirming a 38 amino acid peptide as predicted by the astA gene sequence. Mass spectrometry analysis of EAST1 and of two generated peptides established the presence and suggested the position of two disulfide bridges of EAST1 in the conformations C1-C2 and C3-C4. Polyclonal antibodies were raised against EAST1 in New Zealand white rabbits to a titer of 1:8000 using affinity-purified GST-EAST1 fusion protein and to a titer of 1:100 using HPLC-purified EAST1. The biological activity of various EAST1 preparations was tested using the suckling mouse assay with CD-1 and CFW mice strains, but failed to produce fluid accumulation in the intestine.

Characterization of atypical enteropathogenic Escherichia coli strains harboring the astA gene that were associated with a waterborne outbreak of diarrhea in Japan

The virulence traits of the Escherichia coli strain associated with a waterborne diarrhea outbreak were examined. Forty-one of 75 students (ages 12 to 15) in Akita Prefecture, Japan, showed clinical symptoms. Seven E. coli Ouk:K-:H45 isolates were isolated from the patients as the causative agent of this outbreak. One isolate (EC-3605) showed the presence of E. coli attaching-and-effacing (eaeA) and enteroaggregative E. coli heat-stable enterotoxin-1 (astA) genes and the absence of Shiga toxin (stx1 and stx2) genes. A polymorphic enteropathogenic E. coli (EPEC) adherence factor plasmid was detected in EC-3605 with a major structural gene deletion and a regulatory gene frameshift mutation, revealing that EC-3605 represents an atypical EPEC strain harboring the astA gene. The role that atypical EPEC strains harboring the astA gene play in human disease is unclear. Our results, along with those of others, present a possibility that these strains comprise a distinct category of diarrheagenic E. coli and that astA affects the age distribution of atypical-EPEC infection.