Characterization of a Galactose Specific Adhesin of Enteroaggregative Escherichia coli

Insulin Regulation of Escherichia coli Abiotic Biofilm Formation: Effect of Nutrients and Growth Conditions

Escherichia coli plays an important role in biofilm formation across a wide array of disease and ecological settings. Insulin can function as an adjuvant in the regulation of biofilm levels. The modulation of insulin-regulated biofilm formation by environmental conditions has not been previously described. In the present study, the effects that various environmental growth conditions and nutrients have on insulin-modulated levels of biofilm production were measured. Micropipette tips were incubated with E. coli ATCC^® 25922™ in a Mueller Hinton broth (MH), or a yeast nitrogen base with 1% peptone (YNBP), which was supplemented with glucose, lactose, galactose and/or insulin (Humulin^®-R). The incubation conditions included a shaking or static culture, at 23 °C or 37 °C. After incubation, the biofilm production was calculated per CFU. At 23 °C, the presence of insulin increased biofilm formation. The amount of biofilm formation was highest in glucose > galactose >> lactose, while the biofilm levels decreased in shaking cultures, except for galactose (3-fold increase; 0.1% galactose and 20 μU insulin). At 37 °C, regardless of condition, there was more biofilm formation/CFU under static conditions in YNBP than in MH, except for the MH containing galactose. E. coli biofilm formation is influenced by aeration, temperature, and insulin concentration in combination with the available sugars.

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.

Galactose specific adhesin of enteroaggregative E. coli induces IL-8 secretion via activation of MAPK and STAT-3 in INT-407 cells

BACKGROUND

Enteroaggregative Escherichia coli (EAEC) is one of the most common bacterial pathogens associated with the etiology of persistent diarrhea. A characteristic feature of EAEC-pathogenesis is the induction of profound inflammatory response in the intestinal epithelium. The present study was designed to investigate the underlying mechanism of inflammatory responses induced by a novel galactose specific adhesin of T7 strain of EAEC (EAEC-T7) in human intestinal epithelial cell line (INT-407).

METHODS

INT-407 cells were stimulated with the adhesin in the absence and presence of anti-adhesin (IgG(AD))/d-galactose/H7/staurosporin (inhibitor of PKC)/PD098059 (inhibitor of MEK)/SB203580 (inhibitor of p38-MAPkinase)/AG490 (inhibitor of JAK (-2,-3)/STAT-3 pathway). The expression of activated Raf-1, MEK-1, ERK1/2, JNK, p38-MAPK and STAT-3 was analyzed by Western immunoblot. Release of interleukin-8 (IL-8) was measured by ELISA.

RESULTS

The adhesin was found to induce activation of Raf-1, MEK-1, ERK1/2, p38-MAPK and STAT-3, which was reduced in the presence of IgG(AD)/d-galactose. The activation of Raf-1 was found to be attenuated in the presence of H7/staurosporin. The expression of phosphorylated STAT-3 was downregulated in the presence of AG490 and PD098059. Further, the adhesin induced IL-8 secretion was reduced in the presence of the inhibitors of MEK (PD098059), p38-MAPK (SB203580) and JAK (-2,-3)/STAT-3 pathway (AG490).

CONCLUSIONS

We propose that STAT-3 activation is quintessential for the galactose specific adhesin induced IL-8 secretion by INT-407 cells and must occur in concert with the activation of ERK1/2.

GENERAL SIGNIFICANCE

Our contribution regarding the galactose specific adhesin mediated signaling leads to an improved understanding of the EAEC-pathogenesis and may provide novel therapeutic approaches to combat EAEC infection.

Enteroaggregative Escherichia coli: An Emerging Enteric Food Borne Pathogen

Enteroaggregative Escherichia coli (EAEC) are quite heterogeneous category of an emerging enteric pathogen associated with cases of acute or persistent diarrhea worldwide in children and adults, and over the past decade has received increasing attention as a cause of watery diarrhea, which is often persistent. EAEC infection is an important cause of diarrhea in outbreak and non-outbreak settings in developing and developed countries. Recently, EAEC has been implicated in the development of irritable bowel syndrome, but this remains to be confirmed. EAEC is defined as a diarrheal pathogen based on its characteristic aggregative adherence (AA) to HEp-2 cells in culture and its biofilm formation on the intestinal mucosa with a “stacked-brick” adherence phenotype, which is related to the presence of a 60 MDa plasmid (pAA). At the molecular level, strains demonstrating the aggregative phenotype are quite heterogeneous; several virulence factors are detected by polymerase chain reaction; however, none exhibited 100% specificity. Although several studies have identified specific virulence factor(s) unique to EAEC, the mechanism by which EAEC exerts its pathogenesis is, thus, far unknown. The present review updates the current knowledge on the epidemiology, chronic complications, detection, virulence factors, and treatment of EAEC, an emerging enteric food borne pathogen.

Differential carbohydrate recognition by Campylobacter jejuni strain 11168: influences of temperature and growth conditions

The pathogenic clinical strain NCTC11168 was the first Campylobacter jejuni strain to be sequenced and has been a widely used laboratory model for studying C. jejuni pathogenesis. However, continuous passaging of C. jejuni NCTC11168 has been shown to dramatically affect its colonisation potential. Glycan array analysis was performed on C. jejuni NCTC11168 using the frequently passaged, non-colonising, genome sequenced (11168-GS) and the infrequently passaged, original, virulent (11168-O) isolates grown or maintained under various conditions. Glycan structures recognised and bound by C. jejuni included terminal mannose, N-acetylneuraminic acid, galactose and fucose. Significantly, it was found that only when challenged with normal oxygen at room temperature did 11168-O consistently bind to sialic acid or terminal mannose structures, while 11168-GS bound these structures regardless of growth/maintenance conditions. Further, binding of un-capped galactose and fucosylated structures was significantly reduced when C. jejuni was maintained at 25°C under atmospheric oxygen conditions. These binding differences identified through glycan array analysis were confirmed by the ability of specific lectins to competitively inhibit the adherence of C. jejuni to a Caco-2 intestinal cell line. Our data suggests that the binding of mannose and/or N-acetylneuraminic acid may provide the initial interactions important for colonisation following environmental exposure.

Cellular response induced by a galactose-specific adhesin of enteroaggregative Escherichia coli in INT-407 cells

In the present study, the role of a fimbrial galactose-specific adhesin of the T7 strain of enteroaggregative Escherichia coli (EAEC-T7) in the signal transduction pathways in human small intestinal epithelial cells (INT-407) was explored. The adhesin was purified by anion exchange chromatography using a Mono Q HR5/5 column in the AKTA purifier system. The characteristic stacked brick pattern of aggregative adherence of EAEC-T7 to INT-407 cells was found to be inhibited in the presence of immunoglobulin G against the purified adhesin as well as d-galactose. The adhesin induced a significant increase in the intracellular calcium concentration [Ca(2+)](i) in INT-407 cells, which was reduced in the presence of dantrolene (inhibitor of intracellular calcium stores), verapamil, calciseptin (calcium channel blockers) as well as neomycin [inhibitor of phospholipase C (PLC)]. Further, an increased level of PLCgamma1 and inositol 1,4,5-tri phosphate as well as enhanced activity of protein kinase C (PKC) in the adhesin-stimulated cells were found to be downregulated in the presence of neomycin and U73122 (inhibitors of PLC) and H-7 (inhibitor of PKC), respectively. The adhesin could also induce interleukin-8 secretion from INT-407 cells, which was inhibited in the presence of dantrolene as well as staurosporin (inhibitor of PKC). Collectively, our results have suggested that the galactose-specific adhesin-induced signal transduction pathway might play a crucial role in the EAEC-induced pathogenesis.

Virulence characteristics and the molecular epidemiology of enteroaggregative Escherichia coli isolates from travellers to developing countries

Enteroaggregative Escherichia coli (EAEC) is associated with diarrhoea among travellers to developing countries. EAEC virulence properties predisposing to illness are not clear. Sixty-four EAEC strains identified by a HEp-2 cell assay and isolated from faecal samples from US and European travellers to developing countries were studied for the prevalence of 11 putative virulence genes by PCR: 49 EAEC strains from adults with acute diarrhoea and 15 EAEC strains from adults without diarrhoea. E. coli strains from the stools of healthy travellers to the same region were used as controls. EAEC carrying aggR, aap, astA and set1A were identified individually more often in the stools of subjects with diarrhoea compared with those without diarrhoea (P<0.05). EAEC isolates with two or three of these genes were associated with diarrhoea compared with EAEC isolates without the presence of these genes (P<0.05). Subjects with diarrhoea who shed EAEC isolates positive for these genes were more likely than subjects shedding EAEC negative for these genes to pass stools with gross mucus (57 vs 14 %) and faecal leukocytes (40 vs 7 %) (P<0.05). This study shows the heterogeneity of gene profiles of EAEC strains found in the stools of international travellers and suggests that the presence of aggR, aap, astA or set1A, the number of genes present and stool characteristics may be markers for more virulent EAEC strains.

Galactose-specific fimbrial adhesin of enteroaggregative Escherichia coli: a possible aggregative factor

A galactose-specific adhesin was isolated from the fimbriae of an enteroaggregative Escherichia coli (EAEC) strain. The adhesin was found to be a high molecular weight aggregate of the 18-kDa monomer. The dimeric (36 kDa) and tetrameric (76 kDa) forms appeared in sodium dodecyl sulphate polyacrylamide gel electrophoresis when a higher concentration of the adhesin was used. The IgGAD (IgG against adhesin) obtained from the immune sera raised in rabbits against purified adhesin could detect all three forms of the adhesin even from the crude fimbrial preparation. The IgGAD failed to recognize the adhesin in the presence of galactose, thereby suggesting the antibody-binding site and the sugar-binding site on the adhesin might be same or overlapping. Furthermore, the IgGAD could localize the adhesin exclusively on the fimbriae as observed in immunogold electron microscopy. The aggregative adherence of the bacteria to HEp-2 cells was reduced to 70% in the presence of the IgGAD. A glycoprotein (34 kDa) present in the membrane fraction of HEp-2 cells interacted with the purified adhesin in a galactose-specific manner. The IgGAD could recognize the adhesin from the crude fimbrial preparation of 9 out of 10 clinical isolates of EAEC strains but failed to identify any protein from the crude fimbrial preparation of Salmonella typhimurium (fim +ve as well as fim -ve strain), Vibrio cholerae (WO7) or Escherichia coli DH5alpha.

Enteroaggregative Escherichia coli: epidemiology, virulence and detection

Enteroaggregative Escherichia coli (EAEC) is a subgroup of diarrhoeagenic E. coli (DEC) that during the past decade has received increasing attention as a cause of watery diarrhoea, which is often persistent. EAEC have been isolated from children and adults worldwide. As well as sporadic cases, outbreaks of EAEC-caused diarrhoea have been described. The definition of EAEC is the ability of the micro-organism to adhere to epithelial cells such as HEp-2 in a very characteristic ‘stacked-brick’ pattern. Although many studies searching for specific virulence factor(s) unique for this category of DEC have been published it is still unknown why the EAEC cause persistent diarrhoea. In addition, the aggregative property of EAEC causes a lot of problems in serotyping due to the cells auto-agglutinating. The gold standard for identification of EAEC includes isolation of the agent and an adherence assay using tissue culture, viz. HEp-2 cells. This assay is in most cases reliable; however, emergence of ‘atypical’ EAEC has been described in several publications. In addition, the HEp-2 assay is time consuming, demands a tissue culture lab and trained staff. Several molecular biological assays have been described, however, none show 100 % specificity.

Enteroaggregative Escherichia coli: An emerging pathogen in children

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

A biologically active lectin of enteroaggregative Escherichia coli

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

Enteroaggregative Escherichia coli: an emerging enteric pathogen

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

Enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) are an increasingly important cause of diarrhoea. E. coli belonging to this category cause watery diarrhoea, which is often persistent and can be inflammatory. EAEC have been implicated in sporadic diarrhoea in children and adults, in both developing and developed countries, and have been identified as the cause of several outbreaks worldwide. EAEC are defined by their ability to adhere to epithelial cells in a characteristic "stacked-brick" pattern but are otherwise highly heterogeneous. Genes that could contribute to the pathogenicity of EAEC encode adhesins, toxins, and other factors, all of which are only partially conserved. Practicable tools are needed to improve diagnosis and identify risk factors. EAEC-infected individuals can be treated with fluoroquinolones but there is a need to examine alternative treatment protocols.