Distinctive patterns of adherence of enteropathogenic Escherichia coli to HeLa cells

Curli fimbria: an Escherichia coli adhesin associated with human cystitis

Escherichia coli is the major causative agent of human cystitis. In this study, a preliminary molecular analysis carried out by PCR (polymerase chain reaction) demonstrated that 100% of 31 E. coli strains isolated from patients with recurrent UTIs (urinary tract infections) showed the presence of the curli fimbria gene (csgA). Curli fimbria is known to be associated with bacterial biofilm formation but not with the adhesion of human cystitis-associated E. coli. Therefore, this work aimed to study how curli fimbria is associated with uropathogenic E. coli (UPEC) as an adhesion factor. For this purpose, the csgA gene was deleted from strain UPEC-4, which carries three adhesion factor genes (csgA, fimH and ompA). The wild-type UPEC-4 strain and its mutant (ΔcsgA) were analyzed for their adhesion ability over HTB-9 (human bladder carcinoma), Vero (kidney cells of African green monkey) and HUVEC (human umbilical vein) cells in the presence of α-d-mannose. All the wild-type UPEC strains tested (100%) were able to adhere to all three cell types, while the UPEC-4 ΔcsgA mutant lost its adherence to HTB-9 but continued to adhere to the HUVEC and Vero cells. The results suggest that curli fimbria has an important role in the adhesion processes associated with human UPEC-induced cystitis.

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

Enteropathogenic Escherichia coli (EPEC) induce attaching and effacing (A/E) lesions in enterocytes and produce the bundle-forming pilus (BFP) contributing to the localized adherence (LA) pattern formation on HeLa cells. Enteroaggregative E. coli (EAEC) produce aggregative adherence (AA) on HeLa cells and form prominent biofilms. The ability to produce LA or AA is an important hallmark to classify fecal E. coli isolates as EPEC or EAEC, respectively. E. coli strains of serotype O119:H6 exhibit an LA+ phenotype and have been considered as comprising a clonal group of EPEC strains. However, we have recently identified O119:H6 EPEC strains that produce LA and an AA-like pattern concurrently (LA/AA-like+). In this study, we evaluated the relatedness of three LA/AA-like+ and three LA+ O119:H6 strains by comparing their virulence and genotypic properties. We first found that the LA/AA-like+ strains induced actin accumulation in HeLa cells (indicative of A/E lesions formation) and formed biofilms on abiotic surfaces more efficiently than the LA+ strains. MLST analysis showed that the six strains all belong to the ST28 complex. All strains carried multiple plasmids, but as plasmid profiles were highly variable, this cannot be used to differentiate LA/AA-like+ and LA+ strains. We further obtained their draft genome sequences and the complete sequences of four plasmids harbored by one LA/AA-like+ strain. Analysis of these sequences and comparison with 37 fully sequenced E. coli genomes revealed that both O119:H6 groups belong to the E. coli phylogroup B2 and are very closely related with only 58-67 SNPs found between LA/AA-like+ and LA+ strains. Search of the draft sequences of the six strains for adhesion-related genes known in EAEC and other E. coli pathotypes detected no genes specifically present in LA/AA-like+ strains. Unexpectedly however, we found that a large plasmid distinct from pEAF is responsible for the AA-like phenotype of the LA/AA-like+ strains. Although we have not identified any plasmid genes specifically present in all LA/AA-like+ strains and absent in the LA+ strains, these results suggest the presence of an unknown mechanism to promote the AA-like pattern production and biofilm formation by the LA/AA-like+ strains. Because their ability to produce A/E lesions and biofilm concomitantly could exacerbate the clinical condition of the patient and lead to persistent diarrhea, the mechanism underlying the enhanced biofilm formation by the LA/AA-like+ O119:H6 strains and their spread and involvement in severe diarrheal diseases should be more intensively investigated.

BfpI, BfpJ, and BfpK Minor Pilins Are Important for the Function and Biogenesis of Bundle-Forming Pili Expressed by Enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) remains a significant cause of infant diarrheal illness and associated morbidity and mortality in developing countries. EPEC strains are characterized by their ability to colonize the small intestines of their hosts by a multistep program involving initial loose attachment to intestinal epithelial cells followed by an intimate adhesion phase. The initial loose interaction of typical EPEC with host intestinal cells is mediated by bundle-forming pili (BFP). BFP are type 4b pili (T4bP) based on structural and functional properties shared with T4bP expressed by other bacteria. The major structural subunit of BFP is called bundlin, a T4b pilin expressed from the bfpA gene in the BFP operon, which contains three additional genes that encode the pilin-like proteins BfpI, BfpJ, and BfpK. In this study, we show that, in the absence of the BFP retraction ATPase (BfpF), BfpI, BfpJ, and BfpK are dispensable for BFP biogenesis. We also demonstrate that these three minor pilins are incorporated along with bundlin into the BFP filament and contribute to its structural integrity and host cell adhesive properties. The results confirm that previous findings in T4aP systems can be extended to a model T4bP such as BFP.

IMPORTANCE

Bundle-forming pili contribute to the host colonization strategy of enteropathogenic Escherichia coli. The studies described here investigate the role for three minor pilin subunits in the structure and function of BFP in EPEC. The studies also suggest that these subunits could be antigens for vaccine development.

Fimbria-Encoding Gene yadC Has a Pleiotropic Effect on Several Biological Characteristics and Plays a Role in Avian Pathogenic Escherichia coli Pathogenicity

The extraintestinal pathogen termed avian pathogenic Escherichia coli (APEC) is known to cause colibacillosis in chickens. The molecular basis of APEC pathogenesis is not fully elucidated yet. In this work, we deleted a component of the Yad gene cluster (yadC) in order to understand the role of Yad in the pathogenicity of the APEC strain SCI-07. In vitro, the transcription level of yadC was upregulated at 41°C and downregulated at 22°C. The yadC expression in vivo was more pronounced in lungs than in spleen, suggesting a role in the early steps of the infection. Chicks infected with the wild-type and mutant strains presented, respectively, 80% and 50% mortality rates. The ΔyadC strain presented a slightly decreased ability to adhere to HeLa cells with or without the d-mannose analog compared with the wild type. Real-time PCR (RT-PCR) assays showed that fimH was downregulated (P < 0.05) and csgA and ecpA were slightly upregulated in the mutant strain, showing that yadC modulates expression of other fimbriae. Bacterial internalization studies showed that the ΔyadC strain had a lower number of intracellular bacteria recovered from Hep-2 cells and HD11 cells than the wild-type strain (P < 0.05). Motility assays in soft agar demonstrated that the ΔyadC strain was less motile than the wild type (P < 0.01). Curiously, flagellum-associated genes were not dramatically downregulated in the ΔyadC strain. Taken together, the results show that the fimbrial adhesin Yad contributes to the pathogenicity and modulates different biological characteristics of the APEC strain SCI-07.

Virulence Gene Regulation in Escherichia coli

Escherichia colicauses three types of illnesses in humans: diarrhea, urinary tract infections, and meningitis in newborns. The acquisition of virulence-associated genes and the ability to properly regulate these, often horizontally transferred, loci distinguishes pathogens from the normally harmless commensal E. coli found within the human intestine. This review addresses our current understanding of virulence gene regulation in several important diarrhea-causing pathotypes, including enteropathogenic, enterohemorrhagic,enterotoxigenic, and enteroaggregativeE. coli-EPEC, EHEC, ETEC and EAEC, respectively. The intensely studied regulatory circuitry controlling virulence of uropathogenicE. coli, or UPEC, is also reviewed, as is that of MNEC, a common cause of meningitis in neonates. Specific topics covered include the regulation of initial attachment events necessary for infection, environmental cues affecting virulence gene expression, control of attaching and effacing lesionformation, and control of effector molecule expression and secretion via the type III secretion systems by EPEC and EHEC. How phage control virulence and the expression of the Stx toxins of EHEC, phase variation, quorum sensing, and posttranscriptional regulation of virulence determinants are also addressed. A number of important virulence regulators are described, including the AraC-like molecules PerA of EPEC, CfaR and Rns of ETEC, and AggR of EAEC;the Ler protein of EPEC and EHEC;RfaH of UPEC;and the H-NS molecule that acts to silence gene expression. The regulatory circuitry controlling virulence of these greatly varied E. colipathotypes is complex, but common themes offerinsight into the signals and regulators necessary forE. coli disease progression.

Adhesins of Enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) strains induce morphological changes in infected epithelial cells. The resulting attaching and effacing (A/E) lesion is characterized by intimate bacterial adherence to epithelial cells, with microvillus destruction, cytoskeletal rearrangement, and aggregation of host cytoskeletal proteins. This review presents an overview of the adhesion mechanisms used for the colonization of the human gastrointestinal tract by EPEC. The mechanisms underlying EPEC adhesion, prior to and during the formation of the A/E lesion, and the host cytosolic responses to bacterial infection leading to diarrheal disease are discussed.

Pathogenesis of human diffusely adhering Escherichia coli expressing Afa/Dr adhesins (Afa/Dr DAEC): current insights and future challenges

The pathogenicity and clinical pertinence of diffusely adhering Escherichia coli expressing the Afa/Dr adhesins (Afa/Dr DAEC) in urinary tract infections (UTIs) and pregnancy complications are well established. In contrast, the implication of intestinal Afa/Dr DAEC in diarrhea is still under debate. These strains are age dependently involved in diarrhea in children, are apparently not involved in diarrhea in adults, and can also be asymptomatic intestinal microbiota strains in children and adult. This comprehensive review analyzes the epidemiology and diagnosis and highlights recent progress which has improved the understanding of Afa/Dr DAEC pathogenesis. Here, I summarize the roles of Afa/Dr DAEC virulence factors, including Afa/Dr adhesins, flagella, Sat toxin, and pks island products, in the development of specific mechanisms of pathogenicity. In intestinal epithelial polarized cells, the Afa/Dr adhesins trigger cell membrane receptor clustering and activation of the linked cell signaling pathways, promote structural and functional cell lesions and injuries in intestinal barrier, induce proinflammatory responses, create angiogenesis, instigate epithelial-mesenchymal transition-like events, and lead to pks-dependent DNA damage. UTI-associated Afa/Dr DAEC strains, following adhesin-membrane receptor cell interactions and activation of associated lipid raft-dependent cell signaling pathways, internalize in a microtubule-dependent manner within urinary tract epithelial cells, develop a particular intracellular lifestyle, and trigger a toxin-dependent cell detachment. In response to Afa/Dr DAEC infection, the host epithelial cells generate antibacterial defense responses. Finally, I discuss a hypothetical role of intestinal Afa/Dr DAEC strains that can act as "silent pathogens" with the capacity to emerge as "pathobionts" for the development of inflammatory bowel disease and intestinal carcinogenesis.

Role of virulence factors on host inflammatory response induced by diarrheagenic Escherichia coli pathotypes

ABSTRACT 

Pathogens are able to breach the intestinal barrier, and different bacterial species can display different abilities to colonize hosts and induce inflammation. Inflammatory response studies induced by enteropathogens as Escherichia coli are interesting since it has acquired diverse genetic mobile elements, leading to different E. coli pathotypes. Diarrheagenic E. coli secrete toxins, effectors and virulence factors that exploit the host cell functions to facilitate the bacterial colonization. Many bacterial proteins are delivered to the host cell for subverting the inflammatory response. Hereby, we have highlighted the specific processes used by E. coli pathotypes, by that subvert the inflammatory pathways. These mechanisms include an arrangement of pro- and anti-inflammatory responses to favor the appropriate environmental niche for the bacterial survival and growth.

Enteropathogenic Escherichia coli (EPEC): Does it have a role in colorectal tumourigenesis? A Prospective Cohort Study

BACKGROUND

Despite the characterization of many aetiologic genetic changes. The specific causative factors in the development of sporadic colorectal cancer remain unclear. This study was performed to detect the possible role of Enteropathogenic Escherichia coli (EPEC) in developing colorectal carcinoma.

PATIENTS AND METHOD

Fresh biopsy specimens have been obtained from the colonic mucosa overlying the colorectal cancer as well as from the colon of the healthy controls. Culture, genotyping and virulence of EPEC were done using (nutrient broth culture, and PCR). Strains biochemically identified as Escherichia coli were selected from the surface of a MacConkey's plate and were serogrouped by slide agglutination tests.

RESULTS

From January 2011 to June 2014, 213 colorectal cancer patients (Group 1) and 248 healthy controls (Group 2) were prospectively enrolled in this study. EPEC was positive in 108 (50.7%) in group 1 and 51 (20.6%) in group 2 (P = 0.0001). A significant difference between both groups was observed regarding serotyping, genotyping (eae gene) and virulence category (P = 0.0001). A significant difference between the 2 subgroups of colorectal cancer cases was observed regarding genotyping (eae, bfb genes) and virulence category.

CONCLUSION

The incidence EPEC was higher significantly in patients with colorectal cancer. E. coli in patients with colorectal cancer significantly differed serotypically and genotypically from the E. coli in normal population. E. coli colonization of the colonic mucosa may be a cause colorectal cancer.

Type IV pilus secretins have extracellular C termini

Type IV pili (T4Ps) are surface appendages used by Gram-negative and Gram-positive pathogens for motility and attachment to epithelial surfaces. In Gram-negative bacteria, such as the important pediatric pathogen enteropathogenic Escherichia coli (EPEC), during extension and retraction, the pilus passes through an outer membrane (OM) pore formed by the multimeric secretin complex. The secretin is common to Gram-negative assemblies, including the related type 2 secretion (T2S) system and the type 3 secretion (T3S) system. The N termini of the secretin monomers are periplasmic and in some systems have been shown to mediate substrate specificity. In this study, we mapped the topology of BfpB, the T4P secretin from EPEC, using a combination of biochemical and biophysical techniques that allowed selective identification of periplasmic and extracellular residues. We applied rules based on solved atomic structures of outer membrane proteins (OMPs) to generate our topology model, combining the experimental results with secondary structure prediction algorithms and direct inspection of the primary sequence. Surprisingly, the C terminus of BfpB is extracellular, a result confirmed by flow cytometry for BfpB and a distantly related T4P secretin, PilQ, from Pseudomonas aeruginosa. Keeping with prior evidence, the C termini of two T2S secretins and one T3S secretin were not detected on the extracellular surface. On the basis of our data and structural constraints, we propose that BfpB forms a beta barrel with 16 transmembrane beta strands. We propose that the T4P secretins have a C-terminal segment that passes through the center of each monomer.

IMPORTANCE

Secretins are multimeric proteins that allow the passage of secreted toxins and surface structures through the outer membranes (OMs) of Gram-negative bacteria. To date, there have been no atomic structures of the C-terminal region of a secretin, although electron microscopy (EM) structures of the complex are available. This work provides a detailed topology prediction of the membrane-spanning domain of a type IV pilus (T4P) secretin. Our study used innovative techniques to provide new and comprehensive information on secretin topology, highlighting similarities and differences among secretin subfamilies. Additionally, the techniques used in this study may prove useful for the study of other OM proteins.

Late establishment of the attaching and effacing lesion caused by atypical enteropathogenic Escherichia coli depends on protein expression regulated by Per

Enteropathogenic Escherichia coli (EPEC) is classified as typical (tEPEC) or atypical (aEPEC) based on the presence or absence of the E. coli adherence factor plasmid (pEAF), respectively. The hallmark of EPEC infection is the formation of the attaching and effacing (A/E) lesions on the gut mucosa. We compared the kinetics of A/E lesion formation induced by aEPEC and tEPEC. The examination of infected HEp-2 cells clearly demonstrated delayed A/E lesion formation by aEPEC in comparison to tEPEC. This delay was associated with the expression of locus of enterocyte effacement (LEE)-encoded virulence factors (i.e., intimin and EspD). Indeed, the insertion of a plasmid containing perABC, a transcriptional regulator of virulence factors involved in A/E formation, into aEPEC strains increased and accelerated the formation of A/E lesions. Interestingly, the enhanced expression and translocation of LEE-encoded proteins, such as those expressed in LEE5 (intimin) and LEE4 (EspD), in aEPEC (perABC) was independent of bacterial adhesion. The secretion kinetics of these two proteins representing LEE5 and LEE4 expression correlated with A/E lesion formation. We conclude that the lack of Per in the regulation network of virulence genes is one of the main factors that delay the establishment of A/E lesions induced by aEPEC strains.

Biochemical characteristics, adhesion, and cytotoxicity of environmental and clinical isolates of Herbaspirillum spp

Herbaspirillum bacteria are best known as plant growth-promoting rhizobacteria but have also been recovered from clinical samples. Here, biochemical tests, matrix-assisted laser deionization-time of flight (MALDI-TOF) mass spectrometry, adherence, and cytotoxicity to eukaryotic cells were used to compare clinical and environmental isolates of Herbaspirillum spp. Discrete biochemical differences were observed between human and environmental strains. All strains adhered to HeLa cells at low densities, and cytotoxic effects were discrete, supporting the view that Herbaspirillum bacteria are opportunists with low virulence potential.

Adherent-invasive Escherichia coli (AIEC) in pediatric Crohn's disease patients: phenotypic and genetic pathogenic features

Background

Adherent-invasive Escherichia coli (AIEC) have been implicated in the ethiopathogenesis of Crohn’s disease (CD). In this study, we analyzed a collection of intestinal mucosa-associated E. coli isolates, presenting AIEC phenotypes, isolated from biopsies of CD pediatric patients and non-inflammatory bowel diseases (IBD) controls, in order to investigate their genetic and phenotypic pathogenic features.

Results

A total of 616 E. coli isolates from biopsies of four pediatric CD patients and of four non-IBD controls were collected and individually analyzed. For AIEC identification, adherent isolates were assayed for invasiveness, and the capacity of the adhesive-invasive isolates to survive and replicate intracellularly was determined over macrophages J774. In this way we identified 36 AIEC-like isolates. Interestingly, their relative abundance was significantly higher in CD patients (10%; 31/308) than in non-IBD controls (1%; 5/308) (χ2 = 38.96 p < 0.001). Furthermore pulsed field gel electrophoresis (PFGE) and randomly amplified polymorphic DNA (RAPD) techniques were applied to analyze the clonality of the 36 AIEC-like isolates. The results obtained allowed us to identify 27 distinct genotypes (22 from CD patients and 5 from non-IBD controls). As for the AIEC prototype strain LF82, all 27 AIEC genotypes presented an aggregative pattern of adherence (AA) that was inhibited by D-mannose, indicating that adhesiveness of AIEC is likely mediated by type 1 pili. PCR analisys was used to investigate presence of virulence genes. The results indicated that among the 27 AIEC isolates, the incidence of genes encoding virulence factors K1 (χ2 = 6.167 P = 0.013), kpsMT II (χ2 = 6.167 P = 0.013), fyuA (χ2 = 6.167 P = 0.013), and ibeA (χ2 = 8.867 P = 0.003) was significantly higher among AIEC strains isolated from CD patients than non-IBD controls.

Conclusions

The identification of AIEC strains in both CD and non-IBD controls, confirmed the “pathobiont” nature of AIEC strains. The finding that AIEC-like isolates were more abundant in CD patients, indicates that a close association of these strains with CD may also exists in pediatric patients.

Adhesive and invasive capacities of Edwardsiella tarda isolated from South American sea lion

Edwarsiella tarda is a zoonotic bacterium that can be isolated from humans, animals and the environment. Although E. tarda is primarily considered a fish pathogen, it is the only species of its genus considered to be pathogenic for humans as well. A survey of zoonotic intestinal bacteria in fresh feces from South American sea lions (SASL) Otaria flavescens, reported E. tarda as the most frequently isolated species. In this study, we used HEp-2 cells to establish in vitro the adherence and invasive ability of 17 E. tarda strains isolated from SASL fecal material. All the strains were able to adhere and invade HEp-2 cells with adhesion and invasion percentages ranging from 56 to 100% and 21 to 74%, respectively. Despite the expression of these pathogenic factors, further investigation is needed to determine whether this bacterium could play a role as primary pathogen for this and other species of pinnipeds.

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.

Two novel EHEC/EAEC hybrid strains isolated from human infections

The so far highest number of life-threatening hemolytic uremic syndrome was associated with a food-borne outbreak in 2011 in Germany which was caused by an enterohemorrhagic Escherichia coli (EHEC) of the rare serotype O104:H4. Most importantly, the outbreak strain harbored genes characteristic of both EHEC and enteroaggregative E. coli (EAEC). Such strains have been described seldom but due to the combination of virulence genes show a high pathogenicity potential. To evaluate the importance of EHEC/EAEC hybrid strains in human disease, we analyzed the EHEC strain collection of the German National Reference Centre for Salmonella and other Bacterial Enteric Pathogens (NRC). After exclusion of O104:H4 EHEC/EAEC strains, out of about 2400 EHEC strains sent to NRC between 2008 and 2012, two strains exhibited both EHEC and EAEC marker genes, specifically were stx2 and aatA positive. Like the 2011 outbreak strain, one of the novel EHEC/EAEC harbored the Shiga toxin gene type stx2a. The strain was isolated from a patient with bloody diarrhea in 2010, was serotyped as O59:H⁻, belonged to MLST ST1136, and exhibited genes for type IV aggregative adherence fimbriae (AAF). The second strain was isolated from a patient with diarrhea in 2012, harbored stx2b, was typed as Orough:H⁻, and belonged to MLST ST26. Although the strain conferred the aggregative adherence phenotype, no known AAF genes corresponding to fimbrial types I to V were detected. In summary, EHEC/EAEC hybrid strains are currently rarely isolated from human disease cases in Germany and two novel EHEC/EAEC of rare serovars/MLST sequence types were characterized.

Quorum-sensing gene luxS regulates flagella expression and Shiga-like toxin production in F18ab Escherichia coli

To investigate the effect of the luxS gene on the expression of virulence factors in Shiga-like toxin producing and verotoxin-producing Escherichia coli, the luxS gene from E. coli 107/86 (wild type, O139:H1:F18ab, Stx2e) was deleted. The successful deletion of luxS was confirmed by bioluminescence assays. The luxS deletion mutant exhibited changed flagella-related phenotypes, like impaired expression of flagella, decreased flagella motility, reduced biofilm formation, and reduced ability to induce pro-immunity response in host cells, which were restored after complementation with the intact luxS gene. The mutant strain also displayed attenuated production of Stx2e. This study provides new information to the crucial function of luxS in regulating Shiga-like toxin producing E. coli virulence.

Haemophilus influenzae porine ompP2 gene transfer mediated by graphene oxide nanoparticles with effects on transformation process and virulence bacterial capacity

Background

H. influenzae is a natural competent bacterium that can uptake DNA from the environment and recombine into bacterial genome. The outbreaks of Brazilian purpuric fever, heavily polluted areas of a different H. influenzae biogroup - aegyptius - as well as gene transference between Neisseria meningitis make the transformation process an important evolutionary factor. This work studied the horizontal transference of the ompP2 gene from a multiresistant strain of H. influenzae 07 (NTHi), under the influence of graphene oxide nanoparticles in order to mimic an atmosphere rich in suspended particles and this way verify if the CFU transformants number was increased.

Material and methods

In this article the gene ompP2 was transformed into different strains of H. influenzae mediated or not by graphene oxide nanoparticles in suspension, followed by the adhesion tests in Hec-1B (human endometrium adenocarcinoma) and A549 (pulmonary epithelial carcinoma) cells lines. The transformation frequency and the adhesion capacity were determined in all the mutants to which the ompP2 gene was transferred and compared to their wild type strains.

Results

The nanoparticles increased the transformation ratio of one particular strain isolated from a pneumonia case. The adhesion patterns to A549 and Hec1b cell lines of these mutated bacteria has their capacity increased when compared to the wild type.

Conclusions

Graphene oxide nanoparticles aid the transformation process, helping to increase the number of CFUs, and the mutants generated with the ompP2 gene from a H. influenzae resistant strain not only present a chloramphenicol resistance but also have an increased adherence patterns in A549 and Hec1B cell lines.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

relA enhances the adherence of enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) is a known causative agent of diarrhea in children. In the process of colonization of the small intestine, EPEC synthesizes two types of adhesins, the bundle-forming pilus (BFP) and intimin. The BFP pilus is an adhesin associated with the initial stages of adherence of EPEC to epithelial cells, while the outer membrane protein intimin carries out the intimate adherence that takes place at the third stage of infection. BFP is encoded by the bfp operon located in plasmid EAF, present only in typical EPEC isolates, while eae, the gene that encodes intimin is situated in the LEE, a chromosomal pathogenicity island. Transcription of bfp and eae is regulated by the products of the perABC operon, also present in plasmid EAF. Here we show that deletion of relA, that encodes a guanosine penta and tetraphosphate synthetase impairs EPEC adherence to epithelial cells in vitro. In the absence of relA, the transcription of the regulatory operon perABC is reduced, resulting in lower levels of BFP and intimin. Bacterial adherence, BFP and intimin synthesis and perABC expression are restored upon complementation with the wild-type relA allele.

Interleukin-8 Secretion by Epithelial Cells Infected with Diffusely AdherentEscherichia coliPossessing Afa Adhesin-Coding Genes

Escherichia coli that adhere sparsely to human epithelial (HEp-2) cells are known as diffusely adherent E. coli(DAEC) and considered potentially diarrheagenic. The role of the afimbrial adhesive sheath (Afa)-identified originally as a uropathogenic factor-in diffuse adhesion is now understood. However, the role of DAEC in diarrheal disease remains controversial. Recently, ability to induce interleukin-8 (IL-8) secretion from intestinal epithelial cells has been suggested as one of the properties of enterovirulent bacteria. In this study, we examined whether DAEC strains possessing Afa genes induced IL-8 in cultures of human carcinoma epithelial cells (e.g., HEp-2, Caco-2, and T84). Nineteen afa-positive DAEC strains were examined for their ability to induce IL-8 secretion, and only 7 strains (37%; 7/19) induced IL-8 as much as enteroaggregative E. coli did. No marked differences in adhesion were observed between high and low inducers. Diffusive adhesiveness itself is unlikely to be sufficient to induce IL-8. All high inducers were motile and others were nonmotile. Additional stimulation by flagella may be required to cause high levels of chemokine induction. Motility or presence of flagella can be an important criterion to predict DAEC diarrheagenicity at clinical laboratories.

Epithelial Cells Secrete Interleukin-8 in Response to Adhesion and Invasion of Diffusely AdheringEscherichia coliLacking Afa/Dr Genes

Escherichia coli that sparsely adhere to human epithelial cells are known as diffusely adherent E. coli (DAEC), and the role of the Afa/Dr family of adhesins is now understood. Strains that do not possess Afa/Dr, however, comprise another group of DAEC, of which the pathogenicity remains unknown. The ability to induce interleukin-8 (IL-8) secretion from intestinal epithelial cells might be a feature of enterovirulent bacteria. We previously found that some Afa/Dr DAEC strains induce IL-8 by stimulating epithelial cells with flagella. The present study examines whether non-Afa/Dr DAEC can induce IL-8 in epithelial cells (HEp-2, INT407, and T84). Among 21 strains, 11 (52%; 11/21) induced as much IL-8 as high inducer strains of Afa/Dr DAEC. Adhesion did not significantly differ between high and low inducers; therefore diffuse adhesion alone is probably insufficient to induce IL-8. It was shown that IL-8 induction and the number of intracellular bacteria directly correlated. Wortmannin, an inhibitor of the phosphatidylinositol-3-phosphate kinase, reduced both intracellular bacteria and IL-8 secretion. Motile strains were significantly more prevalent among high (10/11) than low (4/10) inducers. However, 4 low invasive strains hardly induced IL-8 despite their motility. In conclusion, some non-Afa/Dr DAEC invoke the induction of high levels of inflammatory cytokines. Unlike Afa/Dr DAEC, however, non-Afa/Dr strains may require invasion to cause strong induction. These non-Afa/Dr high inducers can be enteropathogenic for the cytokine-inducing properties.

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

Genotypic and phenotypic analysis of diarrheagenic Escherichia coli strains isolated from Brazilian children living in low socioeconomic level communities

Background

Childhood diarrheal diseases remain highly endemic in developing areas of Brazil. The importance of Escherichia coli among children with diarrhea in these areas was unknown. This study determined the prevalence of different E. coli categories in symptomatic and asymptomatic children from low socioeconomic level rural communities in southeastern Brazil.

Methods

A total of 560 stool samples were collected from 141 children with diarrhea (< 10 years) and 419 apparently healthy controls who resided in 23 communities. E. coli isolates (n = 1943) were subjected to two multiplex PCRs developed for the detection of enteropathogenic E. coli (EPEC), enteroaggregative E. coli (EAEC), diffusely adherent E. coli (DAEC), enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), and Shiga toxin-producing E. coli (STEC). Strains were also examined for the presence of EPEC, EAEC, and DAEC by assays of adhesion to HEp-2 cells and by hybridization with specific DNA probes.

Results

Diarrheagenic E. coli strains were isolated from 253 (45.2%) children, and were associated with diarrhea in children aged < 5 years (p < 0.001). EAEC (20.9%), DAEC (11.6%), EPEC (9.3%) were the most frequent pathotypes, followed by ETEC (2.7%), EIEC (0.5%), and STEC (0.2%). Depending of the assay, EPEC, EAEC, and DAEC (collectively termed enteroadherent E. coli) strains were isolated in 45% to 56% of diarrhea cases, a significantly higher incidence than in controls (P < 0.05). Individually, only DAEC showed significant association with diarrhea (p < 0.05), particularly in children aged 2–5 years.

Conclusion

This study indicates that enteroadherent E. coli is an important cause of diarrhea in children living in low socioeconomic level communities in southeastern Brazil. Our results reveal that the PCR1 assay is an excellent tool for the identification of EAEC and DAEC.

Shiga toxin-producing Escherichia coli O104:H4: an emerging pathogen with enhanced virulence

Pathogenic Escherichia coli are genetically diverse and encompass a broad variety of pathotypes, such as enteroaggregative E. coli (EAEC) or enterohemorrhagic E. coli (EHEC), which cause distinct clinical syndromes. The historically large 2011 German outbreak of hemolytic uremic syndrome (HUS), caused by a Shiga-toxin producing E. coli (STEC) of the serotype O104:H4, illustrated the emerging importance of non-O157 STEC. STEC O104:H4, with features characteristic of both enteroaggregative E. coli and enterohemorrhagic E. coli, represents a unique and highly virulent pathotype. The German outbreak both allowed for the evaluation of several potential therapeutic approaches to STEC-induced HUS and emphasizes the importance of early and specific detection of both O157 and non-O157 STEC.

Dissection of the role of pili and type 2 and 3 secretion systems in adherence and biofilm formation of an atypical enteropathogenic Escherichia coli strain

Atypical enteropathogenic Escherichia coli (aEPEC) strains are diarrheal pathogens that lack bundle-forming pilus production but possess the virulence-associated locus of enterocyte effacement. aEPEC strain 1551-2 produces localized adherence (LA) on HeLa cells; however, its isogenic intimin (eae) mutant produces a diffuse-adherence (DA) pattern. In this study, we aimed to identify the DA-associated adhesin of the 1551-2 eae mutant. Electron microscopy of 1551-2 identified rigid rod-like pili composed of an 18-kDa protein, which was identified as the major pilin subunit of type 1 pilus (T1P) by mass spectrometry analysis. Deletion of fimA in 1551-2 affected biofilm formation but had no effect on adherence properties. Analysis of secreted proteins in supernatants of this strain identified a 150-kDa protein corresponding to SslE, a type 2 secreted protein that was recently reported to be involved in biofilm formation of rabbit and human EPEC strains. However, neither adherence nor biofilm formation was affected in a 1551-2 sslE mutant. We then investigated the role of the EspA filament associated with the type 3 secretion system (T3SS) in DA by generating a double eae espA mutant. This strain was no longer adherent, strongly suggesting that the T3SS translocon is the DA adhesin. In agreement with these results, specific anti-EspA antibodies blocked adherence of the 1551-2 eae mutant. Our data support a role for intimin in LA, for the T3SS translocon in DA, and for T1P in biofilm formation, all of which may act in concert to facilitate host intestinal colonization by aEPEC strains.

Enterotoxigenic Escherichia coli CS21 pilus contributes to adhesion to intestinal cells and to pathogenesis under in vivo conditions

Colonization surface antigens (CSs) represent key virulence-associated factors of enterotoxigenic Escherichia coli (ETEC) strains. They are required for gut colonization, the first step of the diarrhoeal disease process induced by these bacteria. One of the most prevalent CSs is CS21, or longus, a type IV pili associated with bacterial self-aggregation, protection against environmental stresses, biofilm formation and adherence to epithelial cell lines. The objectives of this study were to assess the role of CS21 in adherence to primary intestinal epithelial cells and to determine if CS21 contributes to the pathogenesis of ETEC infection in vivo. We evaluated adherence of a CS21-expressing wild-type ETEC strain and an isogenic CS21-mutant strain to pig-derived intestinal cell lines. To determine the role of CS21 in pathogenesis we used the above ETEC strains in a neonatal mice challenge infection model to assess mortality. Quantitative adherence assays confirmed that ETEC adheres to primary intestinal epithelial cells lines in a CS21-dependent manner. In addition, the CS21-mediated ETEC adherence to cells was specific as purified LngA protein, the CS21 major subunit, competed for binding with the CS21-expressing ETEC while specific anti-LngA antibodies blocked adhesion to intestinal cells. Neonatal DBA/2 mice died after intra-stomach administration of CS21-expressing strains while lack of CS21 expression drastically reduced the virulence of the wild-type ETEC strain in this animal model. Collectively these results further support the role of CS21 during ETEC infection and add new evidence on its in vivo relevance in pathogenesis.

Adhesion of Diarrheagenic Escherichia coli and Inhibition by Glycocompounds Engaged in the Mucosal Innate Immunity

Escherichia coli colonizes the human intestine shortly after birth, with most strains engaging in a commensal relationship. However, some E. coli strains have evolved toward acquiring genetic traits associated with virulence. Currently, five categories of enteroadherent E. coli strains are well-recognized, and are classified in regard to expressed adhesins and the strategy used during the colonization. The high morbidity associated with diarrhea has motivated investigations focusing on E. coli adhesins, as well on factors that inhibit bacterial adherence. Breastfeeding has proved to be the most effective strategy for preventing diarrhea in children. Aside from the immunoglobulin content, glycocompounds and oligosaccharides in breast milk play a critical role in the innate immunity against diarrheagenic E. coli strains. This review summarizes the colonization factors and virulence strategies exploited by diarrheagenic E. coli strains, addressing the inhibitory effects that oligosaccharides and glycocompounds, such as lactoferrin and free secretory components, exert on the adherence and virulence of these strains. This review thus provides an overview of experimental data indicating that human milk glycocompounds are responsible for the universal protective effect of breastfeeding against diarrheagenic E. coli pathotypes.

F18ab Escherichia coli flagella expression is regulated by acyl-homoserine lactone and contributes to bacterial virulence

To investigate the effect of the Quorum Sensing (QS)-I system on the expression of virulence factors in Shiga toxin producing and verotoxin-producing Escherichia coli (STEC and VTEC), the yenI gene from Yersinia enterocolitica was cloned into E. coli F18ab 107/86. Recombinant E. coli transformed with yenI produced acyl-homoserine lactone synthase (AHL), as measured using cross-streaking assays with the reporter biosensor strain Chromobacterium violaceum CV026. The AI-1 positive recombinant F18ab E. coli exhibited impaired expression of flagella, decreased motility, reduced biofilm formation and AI-2 production, as well as attenuated adherence and invasion on IPEC-J2 cells. This study provides new insights to the crucial function of AI-1 in regulating STEC virulence.

Prevalence and antibiotic resistance profiles of diarrheagenic Escherichia coli strains isolated from food items in northwestern Mexico

Diarrheogenic Escherichia coli (DEC) strains are an important cause of intestinal syndromes in the developing world mainly affecting children. DEC strains often infect tourists from developed countries traveling to Mexico, causing so-called "traveler diarrhea". DEC strains are typically transmitted by contaminated food and water; however, the prevalence of these strains in food items that are produced, consumed and sometimes exported in northwestern Mexico has not been evaluated. In this study, we conducted a large microbiological survey of DEC strains in 5162 food items and beverages consumed throughout Sinaloa state during 2008 and 2009. We developed a panel of eight sequential PCR reactions that detected the presence of all DEC categories, including typical or atypical variants. Thermotolerant coliforms (also known as fecal coliforms) and E. coli were detected by conventional bacteriology in 13.4% (692/5162) and 7.92% (409/5162) of food items, respectively. Among 409 E. coli isolates, 13.6% (56/409) belonged to DEC strains. Dairy products (2.8%) were the most contaminated with DEC, while DEC strains were not detected in beverages and ice samples. The pathogenic type that was most commonly isolated was EPEC (78.5%), followed by EAEC (10.7%), STEC (8.9%) and ETEC (1.7%). EHEC, DAEC and EIEC strains were not detected. Approximately 80% of EPEC and EAEC strains were classified as atypical variants; they did not adhere to a culture of HEp-2 cell. Of the isolated DEC strains, 66% showed resistance to at least one commonly prescribed antibiotic. In conclusion, the presence of DEC strains in food items and beverages available in northwestern Mexico is low and may not represent a threat for the general population or those traveling to tourist areas.

Multi-functional analysis of Klebsiella pneumoniae fimbrial types in adherence and biofilm formation

Klebsiella pneumoniae is an opportunistic pathogen frequently associated with nosocomially acquired infections. Host cell adherence and biofilm formation of K. pneumoniae isolates is mediated by type 1 (T1P) and type 3 (MR/K) pili whose major fimbrial subunits are encoded by the fimA and mrkA genes, respectively. The E. coli common pilus (ECP) is an adhesive structure produced by all E. coli pathogroups and a homolog of the ecpABCDE operon is present in the K. pneumoniae genome. In this study, we aimed to determine the prevalence of these three fimbrial genes among a collection of 69 clinical and environmental K. pneumoniae strains and to establish a correlation with fimbrial production during cell adherence and biofilm formation. The PCR-based survey demonstrated that 96% of the K. pneumoniae strains contained ecpA and 94% of these strains produced ECP during adhesion to cultured epithelial cells. Eighty percent of the strains forming biofilms on glass produced ECP, suggesting that ECP is required, at least in vitro, for expression of these phenotypes. The fim operon was found in 100% of the strains and T1P was detected in 96% of these strains. While all the strains examined contained mrkA, only 57% of them produced MR/K fimbriae, alone or together with ECP. In summary, this study highlights the ability of K. pneumoniae strains to produce ECP, which may represent a new important adhesive structure of this organism. Further, it defines the multi-fimbrial nature of the interaction of this nosocomial pathogen with host epithelial cells and inert surfaces.

Escherichia coli virulence factors

Escherichia coli was described in 1885 by a German pediatrician, Theodor Escherich, in the faeces of a child suffering diarrhoea. In 1893, a Danish veterinarian postulated that the E. coli species comprises different strains, some being pathogens, others not. Today the E. coli species is subdivided into several pathogenic strains causing different intestinal, urinary tract or internal infections and pathologies, in animal species and in humans. Since this congress topic is the interaction between E. coli and the mucosal immune system, the purpose of this manuscript is to present different classes of adhesins (fimbrial adhesins, afimbrial adhesins and outer membrane proteins), the type 3 secretion system, and some toxins (oligopeptide, AB, and RTX pore-forming toxins) produced by E. coli, that can directly interact with the epithelial cells of the intestinal, respiratory and urinary tracts.

Escherichia coli: a brief review of diarrheagenic pathotypes and their role in diarrheal diseases in Iran

Diarrheagenic Escherichia coli have developed different strategies for establishment of infection in their host. Understanding these pathogenic mechanisms has led to the development of specific diagnostic tools for identification and categorization of E. coli strains into different pathotypes. This review aims to provide an overview of the various categories of diarrheagenic Escherichia coli and the data obtained in Iran pertaining to these pathotypes.

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.

Retraction of enteropathogenic E. coli type IV pili promotes efficient host cell colonization, effector translocation and tight junction disruption

Type IV pili (Tfp) play a primary role in mediating the adherence of pathogenic bacteria to their hosts. The pilus filament can retract with an immense force. However, the role of this activity in microbial pathogenesis has not been rigorously explored. Experiments performed on volunteers suggested that the retraction capacity of enteropathogenic Escherichia coli (EPEC) Tfp is required for full virulence. Here we review our recent study(1) in which we showed that the retraction capacity of the EPEC Tfp facilitates tight-junction disruption and actin-rich pedestal formation by promoting efficient bacterial protein effector translocation into epithelial host cells. We also present new data using live imaging confocal microscopy suggesting that EPEC adheres to monolayers in microcolonies and that Tfp retraction facilitates significant changes in the microcolony shape, which may be critical for efficient effector delivery. Our studies hence suggest novel insights into the role of pili retraction in EPEC pathogenesis.

Human sepsis-associated Escherichia coli (SEPEC) is able to adhere to and invade kidney epithelial cells in culture

The adhesins of extraintestinal pathogenic Escherichia coli are essential for mediating direct interactions between the microbes and the host cell surfaces that they infect. Using fluorescence microscopy and gentamycin protection assays, we observed that 49 sepsis-associated E. coli (SEPEC) strains isolated from human adults adhered to and invaded Vero cells in the presence of D-mannose (100%). In addition, bacteria concentrations of approximately 2 × 10⁷ CFU/mL were recovered from Vero cells following an invasion assay. Furthermore, PCR analysis of adhesin genes showed that 98.0% of these SEPEC strains tested positive for fimH, 69.4% for flu, 53.1% for csgA, 38.8% for mat, and 32.7% for iha. Analysis of the invasin genes showed that 16.3% of the SEPEC strains were positive for tia, 12.3% for gimB, and 10.2% for ibeA. Therefore, these data suggest that SEPEC adhesion to cell surfaces occurs through non-fimH mechanisms. Scanning electron microscopy showed the formation of microcolonies on the Vero cell surface. SEPEC invasiveness was also confirmed by the presence of intracellular bacteria, and ultrastructural analysis using electron transmission microscopy revealed bacteria inside the Vero cells. Taken together, these results demonstrate that these SEPEC strains had the ability to adhere to and invade Vero cells. Moreover, these data support the theory that renal cells may be the predominant pathway through which SEPEC enters human blood vessels.

Infection strategies of enteric pathogenic Escherichia coli

Enteric Escherichia coli (E. coli) are both natural flora of humans and important pathogens causing significant morbidity and mortality worldwide. Traditionally enteric E. coli have been divided into 6 pathotypes, with further pathotypes often proposed. In this review we suggest expansion of the enteric E. coli into 8 pathotypes to include the emerging pathotypes of adherent invasive E. coli (AIEC) and Shiga-toxin producing enteroaggregative E. coli (STEAEC). The molecular mechanisms that allow enteric E. coli to colonize and cause disease in the human host are examined and for two of the pathotypes that express a type 3 secretion system (T3SS) we discuss the complex interplay between translocated effectors and manipulation of host cell signaling pathways that occurs during infection.

Enterocyte microvillus-derived vesicles detoxify bacterial products and regulate epithelial-microbial interactions

The continuous monolayer of intestinal epithelial cells (IECs) lining the gut lumen functions as the site of nutrient absorption and as a physical barrier to prevent the translocation of microbes and associated toxic compounds into the peripheral vasculature. IECs also express host defense proteins such as intestinal alkaline phosphatase (IAP), which detoxify bacterial products and prevent intestinal inflammation. Our laboratory recently showed that IAP is enriched on vesicles that are released from the tips of IEC microvilli and accumulate in the intestinal lumen. Here, we show that these native "lumenal vesicles" (LVs) (1) contain catalytically active IAP that can dephosphorylate lipopolysaccharide (LPS), (2) cluster on the surface of native lumenal bacteria, (3) prevent the adherence of enteropathogenic E. coli (EPEC) to epithelial monolayers, and (4) limit bacterial population growth. We also find that IECs upregulate LV production in response to EPEC and other Gram-negative pathogens. Together, these results suggest that microvillar vesicle shedding represents a novel mechanism for distributing host defense machinery into the intestinal lumen and that microvillus-derived LVs modulate epithelial-microbial interactions.

Outer membrane targeting, ultrastructure, and single molecule localization of the enteropathogenic Escherichia coli type IV pilus secretin BfpB

Type IV pili (T4P) are filamentous surface appendages required for tissue adherence, motility, aggregation, and transformation in a wide array of bacteria and archaea. The bundle-forming pilus (BFP) of enteropathogenic Escherichia coli (EPEC) is a prototypical T4P and confirmed virulence factor. T4P fibers are assembled by a complex biogenesis machine that extrudes pili through an outer membrane (OM) pore formed by the secretin protein. Secretins constitute a superfamily of proteins that assemble into multimers and support the transport of macromolecules by four evolutionarily ancient secretion systems: T4P, type II secretion, type III secretion, and phage assembly. Here, we determine that the lipoprotein transport pathway is not required for targeting the BfpB secretin protein of the EPEC T4P to the OM and describe the ultrastructure of the single particle averaged structures of the assembled complex by transmission electron microscopy. Furthermore, we use photoactivated localization microscopy to determine the distribution of single BfpB molecules fused to photoactivated mCherry. In contrast to findings in other T4P systems, we found that BFP components predominantly have an uneven distribution through the cell envelope and are only found at one or both poles in a minority of cells. In addition, we report that concurrent mutation of both the T4bP secretin and the retraction ATPase can result in viable cells and found that these cells display paradoxically low levels of cell envelope stress response activity. These results imply that secretins can direct their own targeting, have complex distributions and provide feedback information on the state of pilus biogenesis.

Ribotyping of EPEC isolates from diarrheal and asymptomatic patients in Iran

AIM

We intended to find out the diversity of EPEC isolates among asymptomatic or diarrheal children in Iran using ribotyping.

BACKGROUND

Enteropathogenic Escherichia coli (EPEC) is responsible for gastroenteritis especially in young children.

PATIENTS AND METHODS

A total of 39 EPEC collected strains were serotyped and the presence of virulence genes as well as EAF plasmid among the strains was studied. Adherence assay was also performed. Clonal diversity of the isolates was investigated using ribotyping.

RESULTS

Of 39 studied strains of E. coli, 6 serogroups of EPEC were represented. The presence of the stx gene was ascertained in 7 isolates and the eaeA, eaeB and bfpA genes were harbored by 5, 3 and 1 strains, respectively. Ribotyping yielded 9 different clusters.

CONCLUSION

According to our results there was not a significant correlation between the results of serotyping and those of ribotyping. However, different serotypes of E. coli may belong to the same ribotype clusters and vice versa.

Bacterial-epithelial contact is a key determinant of host innate immune responses to enteropathogenic and enteroaggregative Escherichia coli

BACKGROUND

Enteropathogenic (EPEC) and Enteroaggregative (EAEC) E. coli have similar, but distinct clinical symptoms and modes of pathogenesis. Nevertheless when they infect the gastrointestinal tract, it is thought that their flagellin causes IL-8 release leading to neutrophil recruitment and gastroenteritis. However, this may not be the whole story as the effect of bacterial adherence to IEC innate response(s) remains unclear. Therefore, we have characterized which bacterial motifs contribute to the innate epithelial response to EPEC and EAEC, using a range of EPEC and EAEC isogenic mutant strains.

METHODOLOGY

Caco-2 and HEp-2 cell lines were exposed to prototypical EPEC strain E2348/69 or EAEC strain O42, in addition to a range of isogenic mutant strains. E69 [LPS, non-motile, non-adherent, type three secretion system (TTSS) negative, signalling negative] or O42 [non-motile, non-adherent]. IL-8 and CCL20 protein secretion was measured. Bacterial surface structures were assessed by negative staining Transmission Electron Microscopy. The Fluorescent-actin staining test was carried out to determine bacterial adherence.

RESULTS

Previous studies have reported a balance between the host pro-inflammatory response and microbial suppression of this response. In our system an overall balance towards the host pro-inflammatory response is seen with the E69 WT and to a greater extent O42 WT, which is in fit with clinical symptoms. On removal of the external EPEC structures flagella, LPS, BFP, EspA and EspC; and EAEC flagella and AAF, the host inflammatory response is reduced. However, removal of E69 lymphostatin increases the host inflammatory response suggesting involvement in the bacterial mediated anti-inflammatory response.

CONCLUSION

Epithelial responses were due to combinations of bacterial agonists, with host-bacterial contact a key determinant of these innate responses. Host epithelial recognition was offset by the microbe's ability to down-regulate the inflammatory response. Understanding the complexity of this host-microbial balance will contribute to improved vaccine design for infectious gastroenteritis.

Characterization of IcmF of the type VI secretion system in an avian pathogenic Escherichia coli (APEC) strain

The intracellular multiplication factor (IcmF) protein is a component of the recently described type VI secretion system (T6SS). IcmF has been shown to be required for intra-macrophage replication and inhibition of phagosome-lysosome fusion in Legionella pneumophila. In Vibrio cholerae it is involved in motility, adherence and conjugation. Given that we previously reported that two T6SS genes (hcp and clpV) contribute to the pathogenesis of a septicaemic strain (SEPT362) of avian pathogenic Escherichia coli (APEC), we investigated the function of IcmF in this strain. Further elucidation of the virulence mechanisms of APEC is important because this pathogen is responsible for financial losses in the poultry industry, and is closely related to human extraintestinal pathogenic E. coli (ExPEC) strains, representing a potential zoonotic risk, as well as serving as a reservoir of virulence genes. Here we show that an APEC icmF mutant has decreased adherence to and invasion of epithelial cells, as well as decreased intra-macrophage survival. The icmF mutant is also defective for biofilm formation on abiotic surfaces. Additionally, expression of the flagella operon is decreased in the icmF mutant, leading to decreased motility. The combination of these phenotypes culminates in this mutant being altered for infection in chicks. These results suggest that IcmF in APEC may play a role in disease, and potentially also in the epidemiological spread of this pathogen through enhancement of biofilm formation.

Characterization of IcmF of the type VI secretion system in an avian pathogenic Escherichia coli (APEC) strain

The intracellular multiplication factor (IcmF) protein is a component of the recently described type VI secretion system (T6SS). IcmF has been shown to be required for intra-macrophage replication and inhibition of phagosome-lysosome fusion in Legionella pneumophila. In Vibrio cholerae it is involved in motility, adherence and conjugation. Given that we previously reported that two T6SS genes (hcp and clpV) contribute to the pathogenesis of a septicaemic strain (SEPT362) of avian pathogenic Escherichia coli (APEC), we investigated the function of IcmF in this strain. Further elucidation of the virulence mechanisms of APEC is important because this pathogen is responsible for financial losses in the poultry industry, and is closely related to human extraintestinal pathogenic E. coli (ExPEC) strains, representing a potential zoonotic risk, as well as serving as a reservoir of virulence genes. Here we show that an APEC icmF mutant has decreased adherence to and invasion of epithelial cells, as well as decreased intra-macrophage survival. The icmF mutant is also defective for biofilm formation on abiotic surfaces. Additionally, expression of the flagella operon is decreased in the icmF mutant, leading to decreased motility. The combination of these phenotypes culminates in this mutant being altered for infection in chicks. These results suggest that IcmF in APEC may play a role in disease, and potentially also in the epidemiological spread of this pathogen through enhancement of biofilm formation.

Subpathotypes of Avian Pathogenic Escherichia coli (APEC) Exist as Defined by their Syndromes and Virulence Traits

Avian pathogenic Escherichia coli (APEC) strains cause different types of systemic extraintestinal infections in poultry, collectively termed colibacillosis, which can cause significant economic losses in the poultry industry. To date, there have been no descriptions of genes or characteristics that allow for the classification of avian strains pathotypes responsible for causing specific diseases in their hosts. In this study we aimed to characterize avian E. coli strains representing 4 groups, including one of commensal strains (AFEC – Avian Fecal Escherichia coli) and 3 groups of APEC strains, where each group is responsible for causing a different disease syndrome in their respective hosts (septicemia, omphalitis and swollen head syndrome). We chose to examine several biological characteristics of these strains including: adhesion to eukaryotic cells, pathogenicity levels according to the lethal dose (50%) assay, phylogenetic group and virulence gene profiles. The comparison of strains based on these genotypic and phenotypic traits, using multivariate statisticals tools and complex networks, allowed us to infer information about the population structure of the studied groups. Our results indicate that APEC strains do not constitute a unique homogeneous group, but rather a structured set of subgroups, where each one is associated with a specific infectious syndrome which can possibly be used to define pathotypes or subpathotypes within APEC strains. These results offer new possibilities with which to study the genes responsible for various pathogenetic processes within APEC strains, and for vaccine development. It may be important to consider these subgroups when developing a vaccine in an effort for obtain cross protection, which has not yet been successfully accomplished when working with APEC strains.

Sticky situation: localized adherence of enteropathogenic Escherichia coli to the small intestine epithelium

Enteropathogenic Escherichia coli (EPEC) primarily cause gastrointestinal illness in neonates. They accomplish this by a complex coordinated multistage strategy, whereby the organisms colonize the epithelial lining of the small intestine. This process can be divided into four stages: first, localized, nonintimate adherence; second, type III secretion-mediated injection of effector proteins, third effacement of microvilli and, finally, intimate adherence. In this article, we review the history and current state of knowledge, as well as present potential future directions for further investigating the fascinating processes by which EPEC and related organisms colonize the human intestine and cause disease.

Atypical enteropathogenic Escherichia coli that contains functional locus of enterocyte effacement genes can be attaching-and-effacing negative in cultured epithelial cells

Enteropathogenic Escherichia coli (EPEC) induces a characteristic histopathology on enterocytes known as the attaching-and-effacing (A/E) lesion, which is triggered by proteins encoded by the locus of enterocyte effacement (LEE). EPEC is currently classified as typical EPEC (tEPEC) and atypical EPEC (aEPEC), based on the presence or absence of the EPEC adherence factor plasmid, respectively. Here we analyzed the LEE regions of three aEPEC strains displaying the localized adherence-like (LAL), aggregative adherence (AA), and diffuse adherence (DA) patterns on HEp-2 cells as well as one nonadherent (NA) strain. The adherence characteristics and the ability to induce A/E lesions were investigated with HeLa, Caco-2, T84, and HT29 cells. The adherence patterns and fluorescent actin staining (FAS) assay results were reproducible with all cell lines. The LEE region was structurally intact and functional in all strains regardless of their inability to cause A/E lesions. An EspF(U)-expressing plasmid (pKC471) was introduced into all strains, demonstrating no influence of this protein on either the adherence patterns or the capacity to cause A/E of the adherent strains. However, the NA strain harboring pKC471 expressed the LAL pattern and was able to induce A/E lesions on HeLa cells. Our data indicate that FAS-negative aEPEC strains are potentially able to induce A/E in vivo, emphasizing the concern about this test for the determination of aEPEC virulence. Also, the presence of EspF(U) was sufficient to provide an adherent phenotype for a nonadherent aEPEC strain via the direct or indirect activation of the LEE4 and LEE5 operons.