Adhesion and its role in the virulence of enteropathogenic Escherichia coli

Molecular characterization of Escherichia coli isolated from milk samples with regard to virulence factors and antibiotic resistance

BACKGROUND AND AIM

Raw milk is considered an essential source of nutrition during all stages of human life because it offers a valuable supply of protein and minerals. Importantly, milk is considered a good media for the growth and contamination of many pathogenic bacteria, especially food-borne pathogens such as Escherichia coli. Thus, the objective of this study was to characterize E. coli and detect its virulence factors and antibiotic resistance from raw milk samples.

MATERIALS AND METHODS

Raw milk samples (n=100) were collected from different localities in Qena, Egypt, and investigated for the presence of E. coli using different biochemical tests, IMViC tests, serotyping to detect somatic antigen type, and molecularly by polymerase chain reaction (PCR) tests. The presence of different virulence and antimicrobial genes (hly, eae, stx1, stx2, blaTEM, tetA(A), and tetB genes) in E. coli isolates was evaluated using PCR.

RESULTS

The results demonstrated that 10 out of 100 milk samples were contaminated with E. coli. Depending on serology, the isolates were classified as O114 (one isolate), O27 (two isolates), O111 (one isolate), O125 (two isolates), and untypeable (five isolates) E. coli. The sequencing of partially amplified 16S rRNA of the untypeable isolates resulted in one isolate, which was initially misidentified as untypeable E. coli but later proved as Enterobacter hormaechei. Moreover, antibacterial susceptibility analysis revealed that nearly all isolates were resistant to more than 3 families of antibiotics, particularly to b-lactams, clindamycin, and rifampin. PCR results demonstrated that all E. coli isolates showed an accurate amplicon for the blaTEM and tetA(A) genes, four isolates harbored eae gene, other four harbored tetB gene, and only one isolate exhibited a positive stx2 gene.

CONCLUSION

Our study explored vital methods for identifying E. coli as a harmful pathogen of raw milk using 16S rRNA sequencing, phylogenetic analysis, and detection of virulence factors and antibiotic-resistant genes.

Genome evolution and the emergence of pathogenicity in avian Escherichia coli

Chickens are the most common birds on Earth and colibacillosis is among the most common diseases affecting them. This major threat to animal welfare and safe sustainable food production is difficult to combat because the etiological agent, avian pathogenic Escherichia coli (APEC), emerges from ubiquitous commensal gut bacteria, with no single virulence gene present in all disease-causing isolates. Here, we address the underlying evolutionary mechanisms of extraintestinal spread and systemic infection in poultry. Combining population scale comparative genomics and pangenome-wide association studies, we compare E. coli from commensal carriage and systemic infections. We identify phylogroup-specific and species-wide genetic elements that are enriched in APEC, including pathogenicity-associated variation in 143 genes that have diverse functions, including genes involved in metabolism, lipopolysaccharide synthesis, heat shock response, antimicrobial resistance and toxicity. We find that horizontal gene transfer spreads pathogenicity elements, allowing divergent clones to cause infection. Finally, a Random Forest model prediction of disease status (carriage vs. disease) identifies pathogenic strains in the emergent ST-117 poultry-associated lineage with 73% accuracy, demonstrating the potential for early identification of emergent APEC in healthy flocks.

The Impact of Age and Pathogens Type on the Gut Microbiota in Infants with Diarrhea in Dalian, China

Objective

Diarrhea in infants is a serious gastrointestinal dysfunction characterized by vomiting and watery bowel movements. Without proper treatment, infants will develop a dangerous electrolyte imbalance. Diarrhea is accompanied by intestinal dysbiosis. This study compared the gut microbiota between healthy infants and diarrheic infants. It also investigated the effects of age and pathogen type on the gut microbiota of infants with diarrhea, providing data for the proper treatment for diarrhea in infants.

Materials and Methods

DNA was collected from the fecal samples of 42 Chinese infants with diarrhea and 37 healthy infants. The healthy infants and infants with diarrhea were divided into four age groups: 0-120, 120-180, 180-270, and 270-365 days. Using PCR and 16S rRNA high-throughput sequencing, the diarrhea-causing pathogens in these infants were identified and then categorized into four groups: Salmonella infection, Staphylococcus aureus infection, combined Salmonella and Staphylococcus aureus infection, and others (neither Salmonella nor Staphylococcus aureus).

Results

The species diversity of gut microbiota in diarrheic infants was significantly reduced compared with that in healthy infants. Infants with diarrhea had a lower abundance of Lactobacillus spp. and Bacillus spp. (P < 0.001) and a significant richness of Klebsiella spp. and Enterobacter spp. (P < 0.001). Similar gut microbiota patterns were found in diarrheic infants in all four age groups. However, different pathogenic infections have significant effects on the gut microbiota of diarrheic infants. For instance, the relative abundance of Klebsiella spp. and Streptococcus spp. was significantly increased (P < 0.001) in infants infected with Staphylococcus aureus; meanwhile, the richness of bacteria such as Enterobacter spp. was significantly increased in the Salmonella infection group (P < 0.001).

Conclusion

The microbiota in infants with diarrhea has changed significantly, characterized by decreased species diversity and abundance of beneficial bacteria and significant increase in the proportion of conditional pathogens. Meanwhile, the gut microbiota of infants with diarrhea at different ages was similar, but different pathogenic infections affect the gut microbiota characteristics. Therefore, early identification of changes in gut microbiota in infants with diarrhea and the adoption of appropriate pathogen type-specific interventions may effectively alleviate the disease and reduce adverse reactions.

Molecular Biology of Escherichia Coli Shiga Toxins' Effects on Mammalian Cells

Shiga toxins (Stxs), syn. Vero(cyto)toxins, are potent bacterial exotoxins and the principal virulence factor of enterohemorrhagic Escherichia coli (EHEC), a subset of Shiga toxin-producing E. coli (STEC). EHEC strains, e.g., strains of serovars O157:H7 and O104:H4, may cause individual cases as well as large outbreaks of life-threatening diseases in humans. Stxs primarily exert a ribotoxic activity in the eukaryotic target cells of the mammalian host resulting in rapid protein synthesis inhibition and cell death. Damage of endothelial cells in the kidneys and the central nervous system by Stxs is central in the pathogenesis of hemolytic uremic syndrome (HUS) in humans and edema disease in pigs. Probably even more important, the toxins also are capable of modulating a plethora of essential cellular functions, which eventually disturb intercellular communication. The review aims at providing a comprehensive overview of the current knowledge of the time course and the consecutive steps of Stx/cell interactions at the molecular level. Intervention measures deduced from an in-depth understanding of this molecular interplay may foster our basic understanding of cellular biology and microbial pathogenesis and pave the way to the creation of host-directed active compounds to mitigate the pathological conditions of STEC infections in the mammalian body.

Action of phosphorylated mannanoligosaccharides on immune and hematological responses and fecal consistency of dogs experimentally infected with enteropathogenic Escherichia coli strains

The therapeutic action of phosphorylated mannanoligosaccharides (MOS) was investigated regarding its prebiotic activity on enteropathogenic Escherichia coli (EPEC). Diarrhea was induced in dogs by experimental infection with EPEC strains. Then MOS was supplied once a day, in water for 20 days. Immunological (IgA and IgG), hematological (lymphocytes, neutrophils and monocytes) and bacteriological variables (PCR detection of the eae gene of EPEC recovered from stool culture), as well as occurrence of diarrhea were evaluated. All strains caused diarrhea at 24, 48 and 72 h after infection. PCR results indicated that E. coli isolated from stool culture of all infected animals had the eae gene. There was no significant difference among groups as to number of blood cells in the hemogram and IgA and IgG production. MOS was effective in recovering of EPEC-infected dogs since prebiotic-treated animals recovered more rapidly from infection than untreated ones (p < 0.05). This is an important finding since diarrhea causes intense dehydration and nutrient loss. The use of prebiotics for humans and other animals with diarrhea can be an alternative for the treatment and prophylaxis of EPEC infections.

Persistent diarrhea: still a serious public health problem in developing countries

Diarrhea is still responsible for high rates of morbidity and mortality in children under 5 years of age. The prolongation of the acute episode may cause digestive and absorptive malfunction and, consequently, malnutrition, raising the risk of death. The objective of this review is to supply the most recent knowledge in the field of persistent diarrhea and to contribute to the decrease of its incidence. Some possible etiologic agents may be involved, including viruses, bacteria, and parasites. Treatment must be addressed to avoid malabsorption of the nutrients of the diet, associated with replacement of the hydroelectrolytic losses, to prevent its prolongation. In the great majority of the episodes, antibiotics are not indicated. Breastfeeding, introduction of safe dietary strategies to prevent protein-energy malnutrition, and improvement of sanitary conditions and hygiene are measures to be promoted with the objective of decreasing the morbidity/mortality of the diarrheic disease in children less than 5 years of age.

Occurrence and molecular characterization of enteropathogenic Escherichia coli serotypes isolated from children with diarrhoea in Najaf, Iraq

PURPOSE

Enteropathogenic Escherichia coli (EPEC) are among the most important pathogens infecting children worldwide and are one of the main causes of diarrhoea. The study was carried out to investigate the occurrence of EPEC as a cause of infectious diarrhoea in children younger than 2 years of age and characterize their virulence genes.

MATERIALS AND METHODS

During the study period, a total of 656 faecal specimens from children with diarrhoea and 54 from healthy children were analyzed. E. coli isolates were serotypically identified with EPEC polyvalent and monovalent antisera. The isolated EPEC were examined for the presence of the attaching and effacing (eaeA), bundle-forming pilus (bfpA), Shiga like toxins (stx₁ and stx₂), enterohaemorrhagic E. coli enterohaemolysin (EHEC hlyA) and EPEC adherence factor (EAF) genes by the PCR assay.

RESULTS

The study has shown that 22 (3.4%) had diarrhoea due to EPEC, while no EPEC isolates were detected in asymptomatic children. The highest number of the EPEC isolated belonging to polyvalent 2. The primers encoding virulence genes were subjected to all the EPEC isolates. Only 9.1%, 27.3%, and 9.1% isolates gave positive re sults with intimin (eaeA), bfbA and (EAF) genes, respectively. None of the isolates were positive for stx₁, stx₂, and hlyA genes. Typical EPEC (eaeA⁺, bfpA⁺) was diagnosed in two isolates, while, atypical EPEC was manifested in four isolates.

CONCLUSIONS

According to the results, the frequency of EPEC isolates in Najaf was lower than what has been suspected and the investigation including the use of molecular technique and serotyping, are necessary to allow precise identification and epidemiological study of these pathogens.

Survival of Escherichia coli strains in Mediterranean brackish water in the Bizerte lagoon in northern Tunisia

This study investigated survival and virulence of Escherichia coli strains exposed to natural conditions in brackish water. Two E. coli strains (O126:B16 and O55:B5) were incubated in water microcosms in the Bizerte lagoon in northern Tunisia and exposed for 12 days to natural sunlight in June (231 to 386 W/m2, 26 +/- 1 degrees C, 30 g/L) and in April (227 to 330 W/m2, 17 +/- 1 degrees C, 27 g/L) or maintained in darkness for 21 days (17 +/- 1 degrees C, 27 g/L). The results revealed that sunlight was the most significant inactivating factor (decrease of 3 Ulog within 48 hours for the two strains) compared to salinity and temperature (in darkness). Survival time of the strains was prolonged as they were maintained in darkness. Local strain (E. coli O55:B5) showed better survival capacity (T90 = 52 hours) than E. coli O126:B16 (T90 = 11 h). For both, modifications were noted only for some metabolic activities of carbohydrates hydrolysis. Cytotoxicity of the two strains, tested on Vero cell, was maintained during the period of survival.

Adherence of Bilophila wadsworthia to cultured human embryonic intestinal cells

Adherence of Bilophila wadsworthia to the cultured human embryonic intestinal cell line, Intestine 407 (Int 407), varied among the strains tested from strongly adherent (76-100% cells positive for one or more adherent bacteria) to non- or weakly adherent (0-25% positive cells). Although negative staining revealed that infrequent cells of an adherent strain, WAL 9077, the adherent type-strain, WAL 7959, and a non-adherent strain, WAL 8448, expressed loosely associated fimbrial structures, a role for these structures in adhesion could not be confirmed with either scanning or thin-section electron micrography. Ruthenium red staining of thin-section preparations and subsequent electron microscopy failed to reveal an extensive extracellular polysaccharide layer. SDS-PAGE analysis of crude outer membrane fractions of WAL 9077 and WAL 8448 demonstrated clear differences in their major and minor outer membrane protein components. Thus, we postulate that the adherence of B. wadsworthia to Int 407 cells is mediated by an outer membrane or cell wall component.

Medicinal plant extracts as anti-Escherichia coli O157:H7 agents and their effects on bacterial cell aggregation

Ethanolic extracts of eight Thai medicinal plants (representing five families) that are used as traditional remedies for treating diarrhea were examined with a salt aggregation test for their ability to modulate cell surface hydrophobicity of enterohemorrhagic Escherichia coli strains, including E. coli O157:H7. Four of these medicinal plants, Acacia catechu, Peltophorum pterocarpum, Punica granatum, and Quercus infectoria, have high bacteriostatic and bactericidal activities. The ethanolic extract of Q. infectoria was the most effective against all strains of E. coli, with MICs of 0.12 to 0.98 mg/ml and MBCs of 0.98 to 3.91 mg/ml. The ethanolic extract of P. granatum had MICs of 0.49 to 1.95 mg/ml and MBCs of 1.95 to 3.91 mg/ml. Ethanolic extracts of Q. infectoria, P. pterocarpum, and P. granatum were among the most effective extracts against the two strains of E. coli O157:H7. The other four plants, Andrographis paniculata, Pluchia indica, Tamarindus indica, and Walsura robusta, did not have high bacteriostatic and bactericidal activities but were able to affect hydrophobicity characteristics on their outermost surface. All plants except Q. infectoria had some ability to increase cell surface hydrophobicity. There appears to be no correlation between antibacterial activity and cell aggregative properties.

Phenotypic and genotypic characterisation of Escherichia coli strains serogrouped as enteropathogenic E. coli (EPEC) isolated from pasteurised milk

Fifty-six Escherichia coli strains, serogrouped as EPEC, isolated from three different brands of pasteurised milk commercialised in Rio de Janeiro, Brazil, were tested for enteropathogenicity markers. Most of the strains (71.4%) were adherent to HEp-2 cells. The adherent strains were distributed among 7 EPEC serogroups (O26, O55, O111, O114, O125, O127, O128, O158). Although almost half of these strains (33.9%) presented unrecognisable adherence phenotypes, classical adherence patterns (localised-like, aggregative and diffuse adherence) described for E. coli and epidemiologically associated with diarrheagenic strains were observed. None of the strains showed typical localised adherence, usually associated with EPEC strains, but 4 of them displayed a localised-like adherence (LAL) phenotype, characterised by fewer and less compact microcolonies but that is still associated with diarrheagenic strains as well as strains of non-human origin. Indeed, 3 of these 4 strains were able to elicit the attaching-effacing lesion (FAS-positive), the central feature of EPEC pathogenesis, and hybridised with bfpA and eae DNA probes. The other LAL-positive strain hybridised with the bfpA probe but gave negative results for the eae probe and FAS assays. Interestingly, all LAL-positive strains produced amplicons of 200 bp in the PCR for bfpA, instead of the expected 326 bp fragment. PCR reactions for stx1 and stx2, two shiga-toxin-encoding genes, gave negative results. Typing of LEE-associated genes by PCR showed the profile eae (beta), tir (beta), espA (alpha) and espB (alpha) for one of the LAL-positive strain. The most prevalent adherence phenotype was the aggregative pattern which is observed in strains epidemiologically associated with persistent diarrhea. Additionally, one strain promoted complete detachment of the Hep-2 cell monolayer after 3 h of infection which might be related to the production of citotoxins, a feature that has been increasingly observed in clinical strains. The possession of EPEC-related O and H antigens is no longer deemed an essential characteristic of true pathogenic EPEC strains, emphasising the importance of routinely screen for virulence markers in E. coli strains isolated from foods. Our results are in accordance with data from the literature that demonstrate that environmental strains display atypical features but yet are capable of eliciting the classical A/E lesion and thus must be considered as potentially pathogenic. Further, our results demonstrate the potential of pasteurised milk as a vehicle for transmission of diarrheagenic E. coli in Brazil.

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.

Virulence factors and pathogenicity of Hafnia alvei for gilthead seabream, Sparus aurata L

Virulence factors (eae gene, haemolytic capacity, fimbriae, resistance to the bactericidal effect of serum, siderophore production) and pathogenicity for gilthead seabream, Sparus aurata L., were analysed for 23 Hafnia alvei strains. None of the strains used in LD50 studies were lethal for seabream at doses as high as >10(8) cfu mL(-1). In chronic challenge studies differences in severity of the inflammatory response were observed between strains. On the basis of correlation of the inflammatory response to different strains of H. alvei in seabream with those virulence factors studied, it was only possible to establish a positive correlation between pathogenicity and resistance to the bactericidal effect of fish serum. Gilthead seabream is thus a species with considerable resistance to experimental infection with H. alvei. The bacterium does, however, have the capacity to remain viable in seabream for up to 3 months, without any clinical signs. Hafnia alvei is a well-recognized human and animal pathogen. Thus, as the pathogen can coexist with aquaculture operations, cultured gilthead seabream could represent a risk to human health as a carrier in some circumstances.

EnteropathogenicEscherichia coli: unravelling pathogenesis

Enteropathogenic Escherichia coli (EPEC) is a gram-negative bacterial pathogen that adheres to intestinal epithelial cells, causing diarrhoea. It constitutes a significant risk to human health and remains an important cause of infant mortality in developing countries. Although EPEC was the first E. coli strain to be implicated in human disease in the 1940s and 1950s, the mechanisms by which this pathogen induced diarrhoea remained a complete mystery throughout most of the 40 years since its description. It was only during the late 1980s that major advances were made in unravelling the mechanisms behind EPEC pathogenesis. Ever since, progress has been made at a stunning pace and there have been major breakthroughs in identifying the bacterial factors involved in attaching and effacing (A/E) lesion formation, host signal transduction pathways in response to EPEC infection and the genetic basis of EPEC pathogenesis. The rapid pace of discovery is a result of intensive research by investigators in this field and portends that EPEC will soon be among one of the most understood diarrhoea-causing infectious agents. This review aims to trace the progress of EPEC research since its existence was first reported by John Bray in 1945, highlighting the major findings that have revolutionised our understanding of EPEC pathogenesis.

Taxonomic identification of microorganisms by capture and intrinsic fluorescence detection

Quick and accurate detection of microbial contamination is accomplished by a unique combination of leading edge technologies described in this and the accompanying article. Microbe capture chips, used with a prototype fluorescence detector, are capable of statistically sampling the environment for pathogens (including spores), identifying the specific pathogens/exotoxins, and determining cell viability where appropriate.

Virulence-related DNA sequences and adherence patterns in strains of enteropathogenic Escherichia coli

The presence of the genes for Escherichia coli adherence factor (EAF), attaching and effacing lesion (eae) and bundle-forming pili (bfp) in 72 strains identified as enteropathogenic E. coli (EPEC) by slide agglutination was evaluated using hybridization and PCR. The adherence property of these strains was assayed using 3h HeLa cells adherence assay. The results obtained indicated that virulence-associated genes were present in 65% of the strains but only ten (13.9%) isolates were positive for all the three markers (typical EPEC), 37 (51.4%) isolates carried either one or two of these determinants (atypical EPEC) and the remaining 25 (34.7%) were negative for all these genes. In vitro adherence assay showed that 44 (61.1%) strains adhered to HeLa cells with a defined pattern, 13 (18.1%) isolates adhered loosely with no definite pattern and the remaining 15 (20.8%) were non-adherent. Analysis of the results showed a statistically significant association between the presence of the virulence-related genes with adherence of the strains with a defined pattern (P</=0.0001). These results indicated that since over 60% of the strains identified by serogrouping carried at least one of the putative virulence markers, it therefore seems that this simple test is still of value in our setting although the need for a confirmatory test is also indicated.

Asymptomatic infections by diarrheagenic Escherichia coli in children from Misiones, Argentina, during the first twenty months of their lives

Diarrheagenics Escherichia coli are the major agents involved in diarrheal disease in developing countries. The aim of this study was to evaluate the time of appearance of the first asymptomatic infection by the different categories of diarrheagenic E. coli in 44 children since their birth and during the first 20 months of their lives. In all of the children studied, we detected at least one category of diarrheagenic E. coli through the 20 months of the study. 510 diarrheagenic E. coli (33.5%) were obtained from the 1,524 samples collected from the 44 children during the time of the study (31.4% EAggEC, 28.8% EPEC, 27.1% DAEC, and 12.7% ETEC). Neither EHEC nor EIEC were identified. The median age for diarrheagenic E. coli colonization was 7.5 months. The mean weaning period was 12.8 months and the mean age for introduction of mixed feeding (breast fed supplemented) was 3.8 months. A significantly lower incidence of diarrheal disease and asymptomatic infections was recorded among the exclusively breast-fed rather than in the supplemented and non breast-fed infants. For ETEC, EPEC and EAggEC the introduction of weaning foods and complete termination of breast-feeding were associated with an increase of asymptomatic infections.

The role of the epidermal growth factor receptor in microbial infections of the gastrointestinal tract

The epidermal growth factor receptor (EGFr) is a transmembrane glycoprotein with an intrinsic tyrosine kinase. Ligand-binding to the EGFr activates cell signaling, phosphorylates protein kinases, and rearranges cytoskeletal proteins - responses that resemble those induced by microbial attachment to cell surfaces, a process known to be mediated by host cell receptors in a number of cases. This article critically reviews the possible role played by the EGFr in microbial colonization, and discusses how modulation of the EGF-EGFr axis may affect infection of the gastrointestinal tract.

Complete DNA sequence and structural analysis of the enteropathogenic Escherichia coli adherence factor plasmid

The complete nucleotide sequence and organization of the enteropathogenic Escherichia coli (EPEC) adherence factor (EAF) plasmid of EPEC strain B171 (O111:NM) were determined. The EAF plasmid encodes two known virulence-related operons, the bfp operon, which is composed of genes necessary for biosynthesis of bundle-forming pili, and the bfpTVW (perABC) operon, composed of regulatory genes required for bfp transcription and also for transcriptional activation of the eae gene in the LEE pathogenicity island on the EPEC chromosome. The 69-kb EAF plasmid, henceforth designated pB171, contains, besides the bfp and bfpTVW (perABC) operons, potential virulence-associated genes, plasmid replication and maintenance genes, and many insertion sequence elements. Of the newly identified open reading frames (ORFs), two which comprise a single operon had the potential to encode proteins with high similarity to a C-terminal region of ToxB whose coding sequence is located on pO157, a large plasmid harbored by enterohemorrhagic E. coli. Another ORF, located between the bfp and bfpTVW operons, showed high similarity with trcA, a bfpT-regulated chaperone-like protein gene of EPEC. Two sites were found to be putative replication regions: one similar to RepFIIA of p307 or F, and the other similar to RepFIB of R100 (NR1). In addition, we identified a third region that contains plasmid maintenance genes. Insertion elements were scattered throughout the plasmid, indicating the mosaic nature of the EAF plasmid and suggesting evolutionary events by which virulence genes may have been obtained.

A novel chromosomal locus of enteropathogenic Escherichia coli (EPEC), which encodes a bfpT-regulated chaperone-like protein, TrcA, involved in microcolony formation by EPEC

The bfpTVW operon, also known as the per operon, of enteropathogenic Escherichia coli (EPEC) is required for the transcriptional activation of the bfp operon, which encodes the major subunit and assembly machinery of bundle-forming pili (BFP). An immobilized T7-tagged BfpT fusion protein that binds specifically to upstream promoter sequences of bfpA and eae was used to 'fish out' from a promoter library other EPEC chromosomal fragments that are bound by the BfpT protein. After screening for promoters exhibiting bfpTVW-dependent expression, one was identified that was positively regulated by bfpTVW and that is not present in the chromosomes of two non-virulent E. coli laboratory strains, DH5alpha and HB101. Further analysis of this positively regulated promoter in EPEC showed that it resided within a 4.9 kb sequence that is not present in E. coli K12. This locus, located downstream of the potB gene, was found to contain four open reading frames (ORFs): bfpTVW-activated promoter was localized upstream of ORF1. An ORF1 knockout mutant produced less of the BFP structural subunit (BfpA) and formed smaller than normal adherent microcolonies on cultured epithelial cells; however, this mutation did not affect bfp transcription. An ORF1-His6 fusion protein specifically bound the preprocessed and mature forms of the BfpA protein and thus appears to stabilize the former within the cytoplasmic compartment. ORF1 therefore is a newly isolated EPEC chromosomal gene that encodes a chaperone-like protein involved in the production of BFP. Hence, ORF1 was designated trcA (bfpT-regulated chaperone-like protein gene). The TrcA protein also specifically bound 39 kDa and 90 kDa proteins that are expressed by EPEC but not by E. coli K12. The 90 kDa protein was revealed to be intimin, a protein product of the eae gene, which is required for the EPEC attaching/effacing phenotype, suggesting a direct interaction of TrcA with intimin in the cytoplasmic compartment.

Modulation of host cell membrane fluidity: a novel mechanism for preventing bacterial adhesion

Adhesion of bacterial enteropathogens to host mucosal surfaces is a critical primary step in the pathogenesis of diarrheal disease. We investigated the effects of altering the physical properties of eukaryotic cells on bacterial adhesion with the use of a series of three structurally dissimilar membrane fluidizers and several Escherichia coli as test strains. Lipid fluidity of the cell plasma membrane was measured by steady-state fluorescence anisotropy employing the probe 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3, 5-hexatriene. There was a dose-dependent and reversible inhibition of bacterial adhesion with increasing membrane fluidity. Time course experiments indicated that increasing membrane fluidity during the early stages of bacterial adhesion was essential for inhibition of attachment. None of the fluidizers affected the viability of either eukaryotic or prokaryotic cells. These findings demonstrate, for the first time, that changes in plasma membrane physical properties of epithelial cells can prevent microbial adhesion. This also suggests that altering the membrane properties of host cells could form a basis for novel strategies to prevent bacterial adhesion during infection in vivo.

Effect on cell surface hydrophobicity and susceptibility of Helicobacter pylori to medicinal plant extracts

Effects on aqueous extracts of medicinal plants on ten Helicobacter pylori strains were studied by the salt aggregation test to determine the possibility to modulate their cell surface hydrophobicity and by an agar diffusion assay for detection of antimicrobial activity. It was established that aqueous extracts of bearberry and cowberry leaves enhance cell aggregation of all H. pylori strains tested by the salt aggregation test, and the extract of bearberry possessed a remarkable bacteriostatic activity. Pure tannic acid showed a result similar to that of bearberry and cowberry extracts which contained a large amount of tannins. In contrast, extracts of wild camomile and pineapple-weed, which blocked aggregation of H. pylori, contained small amounts of tannins and did not reveal any antimicrobial activity. Tannic acid seems to be the component of bearberry and cowberry aqueous extracts with the highest activity to decrease cell surface hydrophobicity as well as in antibacterial activity against H. pylori.

Effects of orally administered epidermal growth factor on enteropathogenic Escherichia coli infection in rabbits

The increased intestinal absorption induced by epidermal growth factor (EGF) is associated with diffuse lengthening of brush border microvilli. The aim of this study was to examine the in vivo effects of oral administration of EGF during infection with enteropathogenic Escherichia coli. New Zealand White rabbits (4 weeks old) received orogastric EGF daily starting 3 days prior to infection with enteropathogenic E. coli RDEC-1 and were compared with sham-treated infected animals and uninfected controls. Weight gain, food intake, fecal E. coli, and stool consistency were assessed daily. On day 10, segments of jejunum, ileum, proximal, and distal colon were assessed for gram-negative bacterial colonization, disaccharidase activities, and epithelial ultrastructure. Effects of EGF on E. coli RDEC-1 proliferation were studied in vitro. E. coli RDEC-1 caused diarrhea and reduced weight gain. Seven days postinfection, the small and large intestines were colonized with numerous bacteria, brush border microvilli were disrupted, and maltase and sucrase activities were significantly reduced in the jejunum. Daily treatment with EGF prevented the occurrence of diarrhea and reduction of weight gain. These effects were associated with significant inhibition of E. coli colonization in the small and large intestine, improved jejunal maltase and sucrase activities and reduced microvillous injury. EGF did not affect the proliferation of E. coli in vitro. The findings suggest that EGF protects the gastrointestinal tract against colonization by enteropathogenic E. coli.

Association between intraepithelial Escherichia coli and colorectal cancer

BACKGROUND & AIMS

Although multiple studies have focused on Helicobacter pylori, little is known about the mucosa-associated flora of the colon. The aim of this study was to detect bacteria directly in colonic mucosa from patients screened for colorectal cancer.

METHODS

Bacteria were quantified with the polymerase chain reaction and identified by comparative sequence analysis in colonoscopic biopsy specimens from 31 asymptomatic and 34 symptomatic controls with normal colonoscopic findings, 29 patients with colonic adenoma, and 31 patients with colorectal carcinoma. In 41 patients, intra- and extracellular location of bacteria was confirmed with the gentamicin protection assay.

RESULTS

No bacteria were detected in biopsy specimens from 97% of asymptomatic and 69% of symptomatic controls. In contrast, bacterial concentrations of 10(3)-10(5) colony-forming units per microliter were detected in biopsy specimens from both malignant and macroscopically normal tissue in 90% and 93% of patients with adenoma and carcinoma, respectively. E. coli and coli-like bacteria were shown to colonize the colonic mucosa in 82% of these patients. The gentamicin protection assay indicated that E. coli was partially intracellular in 87% of patients with adenoma and carcinoma and in none of the controls.

CONCLUSIONS

The colonic mucosa of patients with colorectal carcinoma but not normal colonic mucosa is colonized by intracellular E. coli.

Divergent signal transduction responses to infection with attaching and effacing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) O157:H7 is an attaching and effacing pathogen that causes hemorrhagic colitis and the hemolytic-uremic syndrome. Although this organism causes adhesion pedestals, the cellular signals responsible for the formation of these lesions have not been clearly defined. We have shown previously that STEC O157:H7 does not induce detectable tyrosine phosphorylation of host cell proteins upon binding to eukaryotic cells and is not internalized into nonphagocytic epithelial cells. In the present study, tyrosine-phosphorylated proteins were detected under adherent STEC O157:H7 when coincubated with the non-intimately adhering, intimin-deficient, enteropathogenic E. coli (EPEC) strain CVD206. The ability to be internalized into epithelial cells was also conferred on STEC O157:H7 when coincubated with CVD206 ([158 +/- 21] % of control). Neither the ability to rearrange phosphotyrosine proteins nor that to be internalized into epithelial cells was evident following coincubation with another STEC O157:H7 strain or with the nonsignaling espB mutant of EPEC. E. coli JM101(pMH34/pSSS1C), which overproduces surface-localized O157 intimin, also rearranged tyrosine-phosphorylated and cytoskeletal proteins when coincubated with CVD206. In contrast, JM101 (pMH34/pSSS1C) demonstrated rearrangement of cytoskeletal proteins, but not tyrosine-phosphorylated proteins, when coincubated with intimin-deficient STEC (strains CL8KO1 and CL15). These findings indicate that STEC O157:H7 forms adhesion pedestals by mechanisms that are distinct from those in attaching and effacing EPEC. Taken together, these findings point to diverging signal transduction responses to infection with attaching and effacing bacterial enteropathogens.

D-lactate production and [14C]succinic acid uptake by adherent and nonadherent Escherichia coli

Escherichia coli isolates of different adherence phenotypes produced different amounts of D-lactate. Alterations of culture conditions did not influence the amount of D-lactate produced. The observed pH decreases in tissue culture medium corresponded with increases in D-lactate concentration. Very little [14C]succinic acid was incorporated into cells during the in vitro incubation of adherent and nonadherent E. coli with HeLa cells, but the amounts of tracer removed from the culture medium by adherent and nonadherent strains differed. The results are further evidence of a difference in the metabolic behavior of adherent and nonadherent E. coli.

Diarrheagenic Escherichia coli

Escherichia coli is the predominant nonpathogenic facultative flora of the human intestine. Some E. coli strains, however, have developed the ability to cause disease of the gastrointestinal, urinary, or central nervous system in even the most robust human hosts. Diarrheagenic strains of E. coli can be divided into at least six different categories with corresponding distinct pathogenic schemes. Taken together, these organisms probably represent the most common cause of pediatric diarrhea worldwide. Several distinct clinical syndromes accompany infection with diarrheagenic E. coli categories, including traveler's diarrhea (enterotoxigenic E. coli), hemorrhagic colitis and hemolytic-uremic syndrome (enterohemorrhagic E. coli), persistent diarrhea (enteroaggregative E. coli), and watery diarrhea of infants (entero-pathogenic E. coli). This review discusses the current level of understanding of the pathogenesis of the diarrheagenic E. coli strains and describes how their pathogenic schemes underlie the clinical manifestations, diagnostic approach, and epidemiologic investigation of these important pathogens.

Escherichia coli in settled-dust and air samples collected in residential environments in Mexico City

Escherichia coli, an important indicator of the presence of fecal material, was isolated from indoor and outdoor environments in Mexico City. The heterogeneity of E. coli was represented by 89 serotypes, most of them coming from settled-dust indoor samples; 21% of them presented antibiotic multiresistance. The numbers of plasmids were higher among the antibiotic-resistant strains. The results of this study suggest that intestinal infections produced by environmental strains could be of more epidemiological impact than previously thought.

Activation of host cell protein kinase C by enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) consists of a group of diarrhea-producing E. coli strains, common in developing countries, which do not produce classical toxins and are not truly invasive. EPEC strains adhere to mammalian cells in an intimate fashion, trigger a localized increase in intracellular calcium levels, and elevate inositol phosphate production. We hypothesized that these mediators could activate host cell protein kinase C (PKC) and tested this idea in vitro with two cultured human cell lines, HeLa cells and T84 cells. Using a recently described subculturing protocol to "induce" or accelerate EPEC adherence, we infected the cells with EPEC at a multiplicity of infection of approximately 100:1 for 30 to 60 min. Under these conditions, EPEC E2348 increased membrane-bound PKC activity 1.5- to 2.3-fold in HeLa cells and T84 cells, respectively. The increase in membrane-bound PKC activity was accompanied by a decrease in cytosolic PKC activity in EPEC-infected HeLa cells. Nonadherent laboratory E. coli strains such as HB101 and H.S. failed to trigger any consistent change in PKC production, similar to the nonadherent mutant strains derived from E2348, JPN15 (plasmid cured) and CVD206 (eaeA). In addition, immunoblots performed on extracts of T84 cells with a monoclonal antibody against PKC-alpha showed an increased PKC content in membranes of EPEC-infected cells. Finally, EPEC-infected T84 cells showed a 60% increase in responsiveness to the E. coli heat-stable toxin. We conclude that mediators produced in response to EPEC adherence activate PKC in intestinal and nonintestinal cells.

Role of type 1 fimbriae in EPEC infections

Several fimbriae have been implicated as potentially important in EPEC adhesion and pathogenesis. EPEC strain E2348/69 produced only bundle forming pili and type 1 fimbriae, and did not produce other accesory adhesins identified in EPEC strain B171. Cloning and mutagenesis of these EPEC fim genes indicated that type 1 pili had no affect on levels or patterns of adhesion to cultured human cells.

Virulence properties of Escherichia coli strains belonging to enteropathogenic (EPEC) serogroups isolated from calves with diarrhea

Nineteen Escherichia coli strains belonging to enteropathogenic (EPEC) serogroups were isolated from calves with diarrhea in Paraná State. Brazil, and studied for virulence markers associated with EPEC or enterohemorrhagic E. coli (EHEC). The 19 isolates belonged to 12 serotypes with isolates of O26:H11, O119:H25 and O114:H- being the most prevalent Localized adherence (LA) was demonstrated for 37% of the isolates, consisting of all four O26:H11, both O114:H- and one O114:H40 isolates. All the LA strains were positive in the fluorescent-actin staining (FAS) test and possessed attaching-effacing E. coli (eae) sequences, but only O114 strains hybridized with the EPEC adherence factor (EAF) probe. None of the strains produced Shiga-like toxins (Verotoxin). Only the O26:H11 strains hybridized with the EHEC plasmid specific (CVD419) probe and were enterohemolytic, properties associated with EHEC strains. This investigation demonstrates that among the bovine strains isolated only those of serogroup O114 behaved as typical EPEC.

Detection system for Escherichia coli-specific virulence genes: absence of virulence determinants in B and C strains

We describe a rational approach to simultaneously test Escherichia coli strains for the presence of known virulence genes in a reverse dot blot procedure. Specific segments of virulence genes of E. coli designed to have similar hybridization parameters were subcloned on plasmids and subsequently amplified by PCR as unlabeled probes in amounts sufficient to be bound to nylon membranes. Various pathogenic isolates and laboratory strains of E. coli were probed for the presence of virulence genes by labeling the genomic DNA of these strains with digoxigenin and then hybridizing them to the prepared nylon membranes. These hybridization results demonstrated that besides the E. coli K-12 safety strain derivatives, E. coli B and C strains are also devoid of genes encoding any of the investigated virulence factors. In contrast, pathogenic E. coli control strains, used to evaluate the method, showed typical hybridization patterns. The described probes and their easy application on a single filter were shown to provide a useful tool for the safety assessment of E. coli strains to be used as hosts in biotechnological processes. This approach might also be used for the identification and characterization of clinically significant E. coli isolates from human and animal species.

Identification of a family of intimins common to Escherichia coli causing attaching-effacing lesions in rabbits, humans, and swine

Intimin, an outer membrane protein encoded by eaeA that mediates close attachment of enteropathogenic bacteria to apical surfaces of epithelial cells, is required for formation of the attaching-effacing lesions and for full pathogenesis of the bacteria. Analysis of the eaeA sequence indicates that there is a high degree of homology at the N termini but less at the C termini of intimins. Antisera specific for the C-terminal third of RDEC-1 intimin, used to screen outer membrane proteins from 50 rabbit enteropathogenic Escherichia coli (EPEC), human EPEC, and human enterohemorrhagic E. coli (EHEC) strains, identified cross-reactive intimins from 24 isolates. Sequence analysis of the eaeA genes from human EPEC O111 and EHEC O26 isolates indicates that their intimins have C termini nearly identical to that of RDEC-1 intimin. Our results suggest that there are at least three families of related intimins and that the presence of intimin similar to that of RDEC-1 is not restricted by serogroup or host specificity.

Clonal structure and virulence factors in strains of Escherichia coli of the classic serogroup O55

Virulence properties and genetic variation as determined by multilocus enzyme electrophoresis were studied in 70 strains of Escherichia coli 055, a common serogroup of enteropathogenic E. coli (EPEC), a major cause of infantile diarrhea in developing countries. Nearly 40% of the strains were originally isolated in Brazil and represented serotypes 055:H6, 055:H7, and 055:H51 and nonmotile (055:H-) strains. The analysis of electrophoretic variants of 20 enzymes defined seven distinct electrophoretic types (ETs). ET 1 was represented by 41% of the strains, including strains which usually hybridized with DNA probes for the intimin gene (eaeA), the EPEC adherence plasmid (EAF), and the gene for the pilin subunit of the bundle-forming pilus (bfpA). The ET 1 strains were also typically serotype 055:H6, displayed localized adherence (LA) in tissue culture assays, and were positive in the fluorescent-actin staining test for intimate cell adherence. These same characteristics were observed in the closely related ETs 2 to 4, which clustered in the same branch as ET 1. No known virulence marker could be identified in ET 6. ET 5 included 23 strains, all of which carried the eaeA gene but otherwise displayed a striking array of distinct virulence traits. This ET was represented by 055:H7 strains with phenotypes as diverse as the simultaneous expression of LA and diffuse adherence and the ability to form a newly described adherence pattern, called LA-like adherence. The results suggest that ET 5 marks a special pathogenic clone with a propensity to acquire virulence factors which may facilitate the emergence of new pathogenic strains.

Characteristics of Escherichia coli strains belonging to enteropathogenic E. coli serogroups isolated in Italy from children with diarrhea

Fifty-five Escherichia coli strains belonging to enteropathogenic E. coli (EPEC) serogroups were examined for phenotypic and genetic factors associated with virulence. The strains were isolated in Italy from children with diarrhea and identified as EPEC by clinical laboratories using commercially available antisera. O:H serotyping showed that 35 strains (27 of O26, O111, and O128 serogroups) belonged to 11 serotypes considered to be classical EPEC O:H serotypes. The other 20 isolates were classified as 15 nonclassical EPEC O:H serotypes. All the potential EPEC virulence factors associated with bacterial adhesion (localized adherence, fluorescentactin staining test positivity, presence of the attaching and effacing [eaeA] gene), the production of verotoxin, and the positivity with the enterohemorrhagic E. coli probe were significantly more frequent among isolates belonging to classical than nonclassical serotypes. Strains displaying an aggregative adhesion and hybridizing with the enteroaggregative DNA probe were found in serogroups O86, O111, and O126. Verotoxin-producing isolates belonged to serogroups O26, O111, and O128. Only one of the isolates hybridized with the EPEC adherence factor (EAF) probe, but 33 strains gave positive results with the eae probe, confirming that the former is more suitable in epidemiological studies in European countries. These results indicate that up to 75% of strains identified as EPEC by commercial antisera may possess potential virulence properties and/or belong to classical EPEC O:H serotypes and suggest that O grouping is still a useful diagnostic tool for presumptive identification of diarrheagenic E. coli in clinical laboratories.

Characterization of Escherichia coli isolated from foals

Serotype, biotype, antibiogram, hemolysin production, fimbrial hemagglutinins, select toxin genes (STb, STaP, LT, slt1 and slt2) and the attaching effacing (eae) gene were determined for 99 foal strains of E. coli. E. coli from diarrheic and normal foals could not be distinguished by serotype, biotype, or antibiogram. Differences (P < or = 0.05) were observed in hemolysin production (11.5% vs 0%) and the expression of mannose-resistant hemagglutinins (23% vs 13%) among E. coli from diarrheic and healthy foals, respectively. Three of the E. coli strains from diarrheic foals were positive with probes for slt genes and one was positive for STb and LT genes. One strain from a healthy foal possessed the STb gene. As determined by the polymerase chain reaction, 8 strains possessed the eae gene. Seven of the 8 strains were from diarrheic foals and one eae-positive strain was from a healthy foal. The slt-positive strains did not possess eae genes and the eae-positive strains did not possess slt genes. These results indicate that enterotoxigenic strains of E. coli are not implicated in any substantial degree in sporadic foal diarrhea. However, the identification of slt-positive and eae-positive strains in foal feces indicate the presence of potentially virulent strains among foals.

Comparison of cytosolic levels of calcium and G actin in diffuse and localised adherent Escherichia coli-infected HeLa cells

In the present study we compared the intracellular level of free calcium ([Ca2+]i) and monomeric (G)/total (G+F) actin ratio in HeLa cells infected with diffuse (DAEC) and localised adherent Escherichia coli (LAEC). The level of [Ca2+]i was increased in both DAEC- and LAEC-infected HeLa cells. However, studies with EGTA- and dantrolene-treated cells and also suspension of cells in Ca(2+)-free buffer suggested that the rise of [Ca2+]i in DAEC-infected cells was due to the influx of Ca2+ from extracellular medium, whereas Ca2+ mobilisation from the intracellular stores was responsible for the enhancement of [Ca2+]i in LAEC-infected cells. It was also evident that the infection of HeLa cells with DAEC and LAEC caused alteration of G/G+F actin ratio as compared to that of control cells. The ratio was much lower in LAEC-infected cells than that of DAEC-infected ones. Moreover, cytochalasin B inhibited both DAEC and LAEC invasion to HeLa cells, suggesting further the role of microfilaments in the invasion process.

Molecular population genetic analysis of emerged bacterial pathogens: selected insights

Research in bacterial population genetics has increased in the last 10 years. Population genetic theory and tools and related strategies have been used to investigate bacterial pathogens that have contributed to recent episodes of temporal variation in disease frequency and severity. A common theme demonstrated by these analyses is that distinct bacterial clones are responsible for disease outbreaks and increases in infection frequency. Many of these clones are characterized by unique combinations of virulence genes or alleles of virulence genes. Because substantial interclonal variance exists in relative virulence, molecular population genetic studies have led to the concept that the unit of bacterial pathogenicity is the clone or cell line. Continued new insights into host parasite interactions at the molecular level will be achieved by combining clonal analysis of bacterial pathogens with large-scale comparative sequencing of virulence genes.

Genotypic and phenotypic characterization of Escherichia coli isolates from dogs manifesting attaching and effacing lesions

Thirteen Escherichia coli isolates from dogs manifesting attaching and effacing lesions were characterized genetically with respect to the presence of the following virulence determinants associated with human enteropathogenic E. coli (EPEC): eaeA, encoding the outer membrane protein intimin; eaeB, which is necessary for inducing signal transduction; bfpA, encoding the bundle-forming pilus; and the EAF (stands for EPEC adherence factor) plasmid. These isolates were also analyzed phenotypically with respect to adherence to mammalian cells in vivo and in vitro. Nine of these 13 isolates were found to be eaeA positive by PCR: four of these nine were eaeB positive. The 5' end, but not the 3' end, of the eaeA gene was amplified by PCR when primers derived from the eaeA gene of EPEC were used. Six and eight of these 13 isolates were found to be bfpA positive and EAF positive, respectively. The bfpA gene and EAF locus were found on high-molecular-weight plasmids, whereas the eaeA and eaeB genes were chromosomally located when present. Only one canine E. coli isolate, 4221, which was positive for eaeA, eaeB, bfpA, and EAF, adhered to HEp-2 cells in a localized manner and was positive in the fluorescence actin staining test. The nine eaeA-positive isolates adhered to the mucosal surface of piglet ileal explants and induced some microvillus effacement. However, when tested in experimentally inoculated gnotobiotic piglets, isolate 4221 did not induce attaching and effacing lesions at any level of the intestinal tract. Our results indicate that canine E. coli isolates associated with attaching and effacing lesions share some properties with human EPEC but form a heterogeneous group.

Monoclonal antibodies specific for the bundle-forming pilus of enteropathogenic Escherichia coli

The bundle-forming pilus (BFP) produced by enteropathogenic Escherichia coli (EPEC) is associated with the presence of a large EPEC adherence factor plasmid and the formation of localized adherence clusters on tissue culture cells. Three mouse monoclonal antibodies (ICA2, ICA3, and ICA4) were produced against BFP purified from EPEC B171 (O111:NM). These monoclonal antibodies reacted in immunoblots with different epitopes of the 19.5-kDa bundlin subunit of BFP of heterologous EPEC. These reagents could serve as diagnostic tools for the identification of EPEC as well as for studying the role of BfpA in the interaction of EPEC with eukaryotic cells.