Enteroaggregative Escherichia Coli infection in a rabbit model

Aggregative Adherence Fimbriae II of Enteroaggregative Escherichia coli Are Required for Adherence and Barrier Disruption during Infection of Human Colonoids

Symptomatic and asymptomatic infection with the diarrheal pathogen enteroaggregative Escherichia coli (EAEC) is associated with growth faltering in children in developing settings. The mechanism of this association is unknown, emphasizing a need for better understanding of the interactions between EAEC and the human gastrointestinal mucosa. In this study, we investigated the role of the aggregative adherence fimbriae II (AAF/II) in EAEC adherence and pathogenesis using human colonoids and duodenal enteroids. We found that a null mutant in aafA, the major subunit of AAF/II, adhered significantly less than wild-type (WT) EAEC strain 042, and adherence was restored in a complemented strain. Immunofluorescence confocal microscopy of differentiated colonoids, which produce an intact mucus layer comprised of the secreted mucin MUC2, revealed bacteria at the epithelial surface and within the MUC2 layer. The WT strain adhered to the epithelial surface, whereas the aafA deletion strain remained within the MUC2 layer, suggesting that the presence or absence of AAF/II determines both the abundance and location of EAEC adherence. In order to determine the consequences of EAEC adherence on epithelial barrier integrity, colonoid monolayers were exposed to EAEC constructs expressing or lacking aafA Colonoids infected with WT EAEC had significantly decreased epithelial resistance, an effect that required AAF/II, suggesting that binding of EAEC to the epithelium is necessary to impair barrier function. In summary, we show that production of AAF/II is critical for adherence and barrier disruption in human colonoids, suggesting a role for this virulence factor in EAEC colonization of the gastrointestinal mucosa.

EX VIVO MODEL OF RABBIT INTESTINAL EPITHELIUM APPLIED TO THE STUDY OF COLONIZATION BY ENTEROAGGREGATIVE ESCHERICHIA COLI

BACKGROUND

The diarrheal syndrome is considered a serious public health problem all over the world and is considered a major cause of morbidity and mortality in developing countries. The high incidence of enteroaggregative Escherichia coli in diarrheal syndromes classified as an emerging pathogen of gastrointestinal infections. After decades of study, your pathogenesis remains uncertain and has been investigated mainly using in vitro models of adhesion in cellular lines.

OBJECTIVE

The present study investigated the interaction of enteroaggregative Escherichia coli strains isolated from childhood diarrhea with rabbit ileal and colonic mucosa ex vivo, using the in vitro organ culture model.

METHODS

The in vitro adhesion assays using cultured tissue were performed with the strains co-incubated with intestinal fragments of ileum and colon over a period of 6 hours. Each strain was tested with three intestinal fragments for each region. The fragments were analysed by scanning electron microscopy.

RESULTS

Through scanning electron microscopy we observed that all strains adhered to rabbit ileal and colonic mucosa, with the typical aggregative adherence pattern of "stacked bricks" on the epithelium. However, the highest degree of adherence was observed on colonic mucosa. Threadlike structures were found in greater numbers in the ileum compared to the colon.

CONCLUSION

These data showed that enteroaggregative Escherichia coli may have a high tropism for the human colon, which was ratified by the higher degree of adherence on the rabbit colonic mucosa. Finally, data indicated that in vitro organ culture of intestinal mucosa from rabbit may be used to elucidate the enteroaggregative Escherichia coli pathogenesis.

Autotransporters but not pAA are critical for rabbit colonization by Shiga toxin-producing Escherichia coli O104:H4

The outbreak of diarrhea and hemolytic uremic syndrome that occurred in Germany in 2011 was caused by a Shiga toxin-producing enteroaggregative Escherichia coli (EAEC) strain. The strain was classified as EAEC due to the presence of a plasmid (pAA) that mediates a characteristic pattern of aggregative adherence on cultured cells, the defining feature of EAEC that has classically been associated with virulence. Here, we describe an infant rabbit-based model of intestinal colonization and diarrhea caused by the outbreak strain, which we use to decipher the factors that mediate the pathogen’s virulence. Shiga toxin is the key factor required for diarrhea. Unexpectedly, we observe that pAA is dispensable for intestinal colonization and development of intestinal pathology. Instead, chromosome-encoded autotransporters are critical for robust colonization and diarrheal disease in this model. Our findings suggest that conventional wisdom linking aggregative adherence to EAEC intestinal colonization is false for at least a subset of strains.

Virulence of the Shiga toxin type 2-expressing Escherichia coli O104:H4 German outbreak isolate in two animal models

In May 2011, a large food-borne outbreak was traced to an unusual O104:H4 enteroaggregative Escherichia coli (EAEC) strain that produced Shiga toxin (Stx) type 2 (Stx2). We developed a mouse model to study the pathogenesis and treatment for this strain and examined the virulence of the isolate for Dutch belted rabbits. O104:H4 strain C227-11 was gavaged into C57BL/6 mice at 10(9) to 10(11) CFU/animal. The infected animals were then given water with ampicillin (Amp; 5 g/liter) ad libitum. The C227-11-infected, Amp-treated C57BL/6 mice exhibited both morbidity and mortality. Kidneys from mice infected with C227-11 showed acute tubular necrosis, a finding seen in mice infected with typical Stx-producing E. coli. We provided anti-Stx2 antibody after infection and found that all of the antibody-treated mice gained more weight than untreated mice and, in another study, that all of the antibody-treated animals lived, whereas 3/8 phosphate-buffered saline-treated mice died. We further compared the pathogenesis of C227-11 with that of an Stx-negative (Stx(-)) O104:H4 isolate, C734-09, and an Stx2(-) phage-cured derivative of C227-11. Whereas C227-11-infected animals lost weight or gained less weight over the course of infection and died, mice infected with either of the Stx(-) isolates did not lose weight and only one mouse died. When the Stx-positive (Stx(+)) and Stx2(-) O104:H4 strains were compared in rabbits, greater morbidity and mortality were observed in rabbits infected with the Stx2(+) isolates than the Stx2(-) isolates. In conclusion, we describe two animal models for EAEC pathogenesis, and these studies show that Stx2 is responsible for most of the virulence observed in C227-11-infected mice and rabbits.

Virulent bacteriophages can target O104:H4 enteroaggregative Escherichia coli in the mouse intestine

In vivo bacteriophage targeting of enteroaggregative Escherichia coli (EAEC) was assessed using a mouse intestinal model of colonization with the O104:H4 55989Str strain and a cocktail of three virulent bacteriophages. The colonization model was shown to mimic asymptomatic intestinal carriage found in humans. The addition of the cocktail to drinking water for 24 h strongly decreased ileal and weakly decreased fecal 55989Str concentrations in a dose-dependent manner. These decreases in ileal and fecal bacterial concentrations were only transient, since 55989Str concentrations returned to their original levels 3 days later. These transient decreases were independent of the mouse microbiota, as similar results were obtained with axenic mice. We studied the infectivity of each bacteriophage in the ileal and fecal environments and found that 55989Str bacteria in the mouse ileum were permissive to all three bacteriophages, whereas those in the feces were permissive to only one bacteriophage. Our results provide the first demonstration that bacterial permissivity to infection with virulent bacteriophages is not uniform throughout the gut; this highlights the need for a detailed characterization of the interactions between bacteria and bacteriophages in vivo for the further development of phage therapy targeting intestinal pathogens found in the gut of asymptomatic human carriers.

A new understanding of enteroaggregative Escherichia coli as an inflammatory pathogen

Enteroaggregative Escherichia coli (EAEC) is an important cause of endemic and epidemic diarrheal disease worldwide. Although not classically considered an inflammatory pathogen in the style of Shigella and Salmonella species, clinical data from patients suggests that inflammatory responses may play an important role during EAEC disease. However, the specific role of inflammation during EAEC pathogenesis has not been investigated in detail. To better understand how EAEC may induce inflammation, we have focused our attention on the intimate interactions between EAEC and the host epithelium and the subsequent induction of host cell signaling events leading to innate immune responses. Here, we discuss our recent findings on the signaling pathway by which EAEC promotes transepithelial migration of polymorphonuclear leukocytes (PMNs), the role of aggregative adherence fimbriae in triggering this event and the implementation of human intestinal xenografts in immunodeficient mice for studying EAEC pathogenesis in vivo. Our findings suggest that EAEC shares conserved mechanisms of inducing PMN recruitment with other intestinal pathogens, providing new insight into the potential pathological consequences of EAEC-induced inflammation.

The fimbriae of enteroaggregative Escherichia coli induce epithelial inflammation in vitro and in a human intestinal xenograft model

BACKGROUND

Enteroaggregative Escherichia coli (EAEC) are increasingly recognized as an important agent of inflammatory and often persistent diarrhea. Although previous studies report on the inflammatory aspects of EAEC pathogenesis, the mechanisms by which EAEC trigger these events are not well understood.

METHODS

EAEC strains harboring mutations in known EAEC virulence determinants were tested in an in vitro model of transepithelial migration of polymorphonuclear neutrophils (PMNs) and in human intestinal xenografts in severe-combined immunodeficient (SCID-HU-INT) mice, a novel model for studying EAEC disease in vivo.

RESULTS

Expression of aggregative adherence fimbriae (AAFs), the principal adhesins of EAEC, was required for EAEC-induced PMN transepithelial migration in vitro. Moreover, constructed plasmids encoding AAF gene clusters demonstrated that the AAF adhesins are sufficient for triggering this event in a nonpathogenic E. coli background. Furthermore, with use of the SCID-HU-INT mouse model, severe tissue damage and infiltration of inflammatory cells was observed in the human tissue after EAEC infection. These pathological marks were strongly related to AAF expression, thus clearly confirming our in vitro findings.

CONCLUSIONS

The present work establishes EAEC as an important inflammatory pathogen and the AAF adhesins as inducers of potentially detrimental immune responses.

Enteroaggregative Escherichia coli induced increase in intracellular calcium concentration modulates cytoskeletal F-actin rearrangement and bacterial entry in INT-407 cells

BACKGROUND

Enteroaggregative Escherichia coli (EAEC) is an emerging enteric pathogen, associated with cases of acute and persistent diarrhoea worldwide. The pathogenesis of EAEC is yet to be understood. In intestinal epithelium, an increase in [Ca²⁺](i) has been attributed due to the action of different enteric pathogens. EAEC was shown to increase [Ca²⁺](i) in HEp-2 cells.The present study was undertaken to investigate the effect of EAEC induced increase in [Ca²⁺](i) oncultured human intestinal epithelial cells.

METHODS

INT-407 cells were infected with EAEC (T8 strain) in the absence and presence of dantrolene (inhibitor of release of Ca²⁺ from intracellular stores)/verapamil (L-type Ca²⁺ channel blocker)/BAPTAAM (Ca²⁺ chelator)/U73122 (PLC inhibitor)/Cytochalasin-D (inhibitor of actin polymerization). [Ca²⁺](i) was estimated using Fura-2/AM. Cytoskeletal rearrangement was assessed by F-actin staining using TRITC-phalloidin. The invasiveness of EAEC-T8 to INT-407 cells was checked by electron microscopy and invasion assay.

RESULTS

A significant increase in [Ca²⁺](i) was observed in EAEC-T8 infected INT-407 cells, which was reduced in presence of dantrolene/verapamil/U73122. EAEC-T8 could induce cytoskeletal F-actin polymerization in INT-407 cells and was found to be invasive in nature. The cytoskeletal rearrangement as well as invasion of EAEC-T8 was attenuated in presence of U73122/dantrolene/BAPTA-AM/verapamil/cytochalasin D.

CONCLUSIONS

EAEC induced increase in [Ca²⁺](i) seems to play a major role in host cytoskeletal F-actin rearrangements leading to invasion of the organism.

GENERAL SIGNIFICANCE

Our study undoubtedly will lead to an improved understanding of EAEC-pathogenesis.

Characterization of Escherichia coli O3 and O21 O antigen gene clusters and development of serogroup-specific PCR assays

Escherichia coli O3 and O21 are associated with enteroaggregative E. coli (EAEC). EAEC strains are often non-typable using the routine agglutination method due to their aggregative phenotype. Typing of E. coli O3 and O21 may also be impeded by cross-reactions with O152 or O83. In this study, the O antigen gene clusters of E. coli O3 and O21 were characterized, and PCR assays based on O antigen specific genes wzx (encoding O unit flippase) and wzy (encoding O unit polymerase) from each strain were developed. By screening against all 186 known E. coli O serotypes, the PCR assays were shown to be highly specific to O3 and O21 respectively. The sensitivity of the assays was determined to be 1 pg per microl of chromosomal DNA and 2 CFU per 10 g of water samples. The PCR assays were also applied to 658 clinical E. coli isolates, and 100% of detection accuracy was obtained. The PCR assays developed here are suitable for the detection and identification of E. coli O3 and O21 strains in environmental and clinical samples.

Lymphocytic colitis: a clue to bacterial etiology

AIM

To find out the role of bacteria as a possible etiological factor in lymphocytic colitis.

METHODS

Twenty patients with histopathological diagnosis of lymphocytic colitis and 10 normal controls were included in this study. Colonoscopic biopsies were obtained from three sites (hepatic and splenic flexures and rectosigmoid region). Each biopsy was divided into two parts. A fresh part was incubated on special cultures for bacterial growth. The other part was used for the preparation of histologic tissue sections that were examined for the presence of bacteria with the help of Giemsa stain.

RESULTS

Culture of tissue biopsies revealed bacterial growth in 18 out of 20 patients with lymphocytic colitis mostly Escherichia coli (14/18), which was found in all rectosigmoid specimens (14/14), but only in 8/14 and 6/14 of splenic and hepatic flexure specimens respectively. In two of these cases, E coli was associated with proteus. Proteus was found only in one case, Klebsiella in two cases, and Staphylococcus aureus in one case. In the control group, only 2 out of 10 controls showed the growth of E coli in their biopsy cultures. Histopathology showed rod-shaped bacilli in the tissue sections of 12 out of 14 cases with positive E coli in their specimen's culture. None of the controls showed these bacteria in histopathological sections.

CONCLUSION

This preliminary study reports an association between E coli and lymphocytic colitis, based on histological and culture observations. Serotyping and molecular studies are in process to assess the role of E coli in the pathogenesis of lymphocytic colitis.