Typing of intimin genes in human and animal enterohemorrhagic and enteropathogenic Escherichia coli: characterization of a new intimin variant

Virulence of enteropathogenic Escherichia coli, a global pathogen

Enteropathogenic Escherichia coli (EPEC) remains an important cause of diarrheal disease worldwide. Research into EPEC is intense and provides a good virulence model of other E. coli infections as well as other pathogenic bacteria. Although the virulence mechanisms are now better understood, they are extremely complex and much remains to be learnt. The pathogenesis of EPEC depends on the formation of an ultrastructural lesion in which the bacteria make intimate contact with the host apical enterocyte membrane. The formation of this lesion is a consequence of the ability of EPEC to adhere in a localized manner to the host cell, aided by bundle-forming pili. Tyrosine phosphorylation and signal transduction events occur within the host cell at the lesion site, leading to a disruption of the host cell mechanisms and, consequently, to diarrhea. These result from the action of highly regulated EPEC secreted proteins which are released via a type III secretion system, many genes of which are located within a pathogenicity island known as the locus of enterocyte effacement. Over the last few years, dramatic increases in our knowledge of EPEC virulence have taken place. This review therefore aims to provide a broad overview of and update to the virulence aspects of EPEC.

Adhesion and colonization of enterohemorrhagic Escherichia coli O157:H7 in cecum of mice

Infectious diseases due to enterohemorrhagic Escherichia coli (EHEC) are characterized by diarrhea, hemorrhagic colitis and hemolytic uremic syndrome. The adherence of EHEC on intestinal epithelial cells is a first step for developing these diseases. In the present study, we examined whether EHEC O157:H7 adhere to intestinal epithelial cells of mice and cause F-actin accumulation in the epithelial cells following the intragastric inoculation of the pathogen. Fecal shedding of the EHEC O157:H7 strain was observed in ICR mice up to 3 weeks. Fecal shedding periods of the type III secretion system-related gene (espA and sepL) deletion mutants were clearly shorter than that of the wild-type EHEC O157:H7 strain. The EHEC O157:H7 colonies were found on the epithelial surfaces of the ceca in association with F-actin accumulation beneath the attached bacteria.

Multiplex PCR assay for identification of human diarrheagenic Escherichia coli

A multiplex PCR assay for the identification of human diarrheagenic Escherichia coli was developed. The targets selected for each category were eae for enteropathogenic E. coli, stx for Shiga toxin-producing E. coli, elt and est for enterotoxigenic E. coli, ipaH for enteroinvasive E. coli, and aggR for enteroaggregative E. coli. This assay allowed the categorization of a diarrheagenic E. coli strain in a single reaction tube.

A mosaic pathogenicity island made up of the locus of enterocyte effacement and a pathogenicity island of Escherichia coli O157:H7 is frequently present in attaching and effacing E. coli

Enteropathogenic Escherichia coli (EPEC) and enterohemorragic E. coli (EHEC) possess a pathogenicity island (PAI), termed the locus of enterocyte effacement (LEE), which confers the capability to cause the characteristic attaching and effacing lesions of the brush border. Due to this common property, these organisms are also termed attaching and effacing E. coli (AEEC). Sequencing of the EHEC O157 genome recently revealed the presence of other putative PAIs in the chromosome of this organism. In this article, we report on the presence of four of those PAIs in a panel of 133 E. coli strains belonging to different pathogroups and serotypes. One of these PAIs, termed O122 in strain EDL 933 and SpLE3 in strain Sakai, was observed in most of the AEEC strains examined but not in the other groups of E. coli. It was also found to contain the virulence-associated gene efa1/lifA. In EHEC O157, PAI O122 is located 0.7 Mb away from the LEE. Conversely, we demonstrated that in many EHEC non-O157 strains and EPEC strains belonging to eight serogroups, PAI O122 and the LEE are physically linked to form a cointegrated structure. This structure can be considered a mosaic PAI that could have been acquired originally by AEEC. In some clones, such as EHEC O157, the LEE-O122 mosaic PAI might have undergone recombinational events, resulting in the insertion of the portion referred to as PAI O122 in a different location.

Adhesion of enteropathogenic Escherichia coli to host cells

Enteropathogenic Escherichia coli (EPEC) adhere to the intestinal mucosa and to tissue culture cells in a distinctive fashion, destroying microvilli, altering the cytoskeleton and attaching intimately to the host cell membrane in a manner termed the attaching and effacing effect. Typical EPEC strains also form three-dimensional microcolonies in a pattern termed localized adherence. Attaching and effacing, and in particular intimate attachment requires an outer membrane adhesin called intimin, which binds to the translocated intimin receptor, Tir. Tir is produced by the bacteria and delivered to the host cell via a type III secretion system. In addition to this well-established adhesin-receptor pair, numerous other adhesin interactions between EPEC and host cells have been described including those between intimin and cellular receptors and those involving a bundle-forming pilus and flagella and unknown receptors. Much additional work is needed before a full understanding of EPEC adhesion to host cells comes to light.

Genotypic and phenotypic characterization of attaching and effacing Escherichia coli (AEEC) isolated from children with and without diarrhoea in Londrina, Brazil

Attaching and effacing Escherichia coli (AEEC) have been implicated in diarrhoea in humans in several countries. A total of 919 E. coli strains, isolated from 125 children with diarrhoea and 98 without diarrhoea, was investigated by PCR for the presence of the EAF, bfp, eae and stx genes. Thirty-four of these isolates were found to carry the eae gene; they were isolated from 27 (79.4 %) children with diarrhoea and seven (20.6 %) controls, in the city of Londrina, Brazil. These strains were investigated for their genotypic and phenotypic characteristics. Different genetic profiles were observed; strains containing the eae gene alone were most common (47.1 %). The characteristic genetic profile of typical enteropathogenic E. coli (EPEC), eae, bfp and EAF, was only found in isolates from children with diarrhoea. The stx gene was not detected in any of the 34 strains studied. Ten (29.4 %) strains were negative in the fluorescent actin-staining test. Localized adhesion (LA) was the most common pattern of adhesion (44.1 %), followed by the aggregative adhesion (AA) (23.5 %) and localized adhesion-like (LAL) (14.7 %) patterns. The results showed a strong association between strains presenting the LA pattern and diarrhoea. Forty-seven per cent of the strains studied belonged to classical O-serogroups of EPEC. The most common serotype found was O119 : H6; these isolates all showed the LA pattern, were positive for fluorescent actin-staining and were associated with diarrhoea. Intimin beta was detected in seven strains, four of which belonged to serotype O119 : H6 and three to serotype ONT : H7; all were associated with diarrhoea. On the other hand, intimin epsilon was detected in two strains of serotype O111 : H38 and one of serotype ONT : H19, isolated from children without diarrhoea. To our knowledge, this is the first report of the occurrence of intimin epsilon in strains of E. coli isolated from humans in Brazil.

An eight-month study of a population of verocytotoxigenic Escherichia coli (VTEC) in a Scottish cattle herd

AIMS

Strains of Verocytotoxin-producing Escherichia coli (VTEC) from Scottish beef cattle on the same farm were isolated during four visits over a period of eight months. Characteristics of these strains were examined to allow comparisons with strains of VTEC associated with human infection.

METHODS AND RESULTS

Strains were characterized to investigate the relationship between these bovine isolates with respect to serotype, Verocytotoxin (VT) type, intimin-type, and presence or absence of the enterohaemolysin genes. VT genes were detected in 176 of 710 (25%) faecal samples tested using PCR, although only 94 (13%) VTEC strains were isolated using DNA probes on cultures. Forty-five different serotypes were detected. Commonly isolated serotypes included O128ab:H8, O26:H11 and O113:H21. VTEC O26:H11 and O113:H21 have been associated with human disease. Strains harbouring the VT2 genes were most frequently isolated during the first three visits to the farm and those with both VT1 and VT2 genes were the major type during the final visit. Of the 94 strains of non-O157 VTEC isolated, 16 (17%) had the intimin gene; nine had the gene encoding beta-intimin and seven strains had an eta/zeta-intimin gene. Forty-one (44%) of 94 strains carried enterohaemolysin genes.

CONCLUSIONS

Different serotypes and certain transmissible characteristics, such as VT-type and the enterohaemolysin phenotype, appeared to be common throughout the VTEC population at different times.

SIGNIFICANCE AND IMPACT OF THE STUDY

Detailed typing and subtyping strains of VTEC as described in this study may improve our understanding of the relationship between bovine VTEC and those found in the human population.

Binding of intimin from enteropathogenic Escherichia coli to lymphocytes and its functional consequences

Intimin-conjugated fluorescent beads bind to spleen CD4 T cells and Peyer's patch, mesenteric lymph node, and cecal follicle lymphocytes, with less binding to lamina propria T cells and intraepithelial lymphocytes. Intimin costimulates proliferation of spleen CD4 T cells and cells from organized lymphoid tissues but does not costimulate cells from the lamina propria of normal or inflamed colon.

Cluster of hemolytic-uremic syndrome caused by Shiga toxin-producing Escherichia coli O26:H11

BACKGROUND

The epidemiology and clinical characteristics of the hemolytic-uremic syndrome (HUS) caused by Escherichia coli O157:H7 are well-known, but HUS attributable to non-O157:H7 Shiga toxin (Stx)-producing E. coli (STEC) are less thoroughly described. Here we report a cluster of HUS cases caused by STEC O26:H11 the most common non-O157:H7 STEC isolated from sporadic cases of HUS in Europe.

METHODS

Three children between 13 and 17 months of age, living in the same small town, developed HUS within an interval of 5 days. We present clinical and microbiologic data on the patients and their infecting isolates.

RESULTS

The clinical course ranged from mild uncomplicated HUS to severe HUS complicated by multiorgan involvement. Microbiologic investigation demonstrated STEC of serotype O26:H11 in stools of all the patients. The phenotypic and molecular characterization of the STEC O26:H11 isolates demonstrated that these strains were identical and, unusual for STEC O26, they harbored the stx2 but not the stx1 gene. None of the patients had evidence of STEC O157:H7 infection either by culture or by E. coli O157 serology. The source of the STEC O26:H11 infection was undetermined.

CONCLUSIONS

Our results demonstrate that diagnostic procedures based on the detection of stx genes and/or Stx production and subsequent subtyping of the isolates using molecular methods are necessary to identify such outbreaks caused by non-O157:H7 STEC.

Verotoxin-producing Escherichia coli in Spain: prevalence, serotypes, and virulence genes of O157:H7 and non-O157 VTEC in ruminants, raw beef products, and humans

In Spain, as in many other countries, verotoxin-producing Escherichia coli (VTEC) strains have been frequently isolated from cattle, sheep, and foods. VTEC strains have caused seven outbreaks in Spain (six caused by E. coli O157:H7 and one by E. coli O111:H- [nonmotile]) in recent years. An analysis of the serotypes indicated serological diversity. Among the strains isolated from humans, serotypes O26:H11, O111:H-, and O157:H7 were found to be more prevalent. The most frequently detected serotypes in cattle were O20:H19, O22:H8, O26:H11, O77:H41, O105:H18, O113:H21, O157:H7, O171:H2, and OUT (O untypeable):H19. Different VTEC serotypes (e.g., O5:H-, O6:H10, O91:H-, O117:H-, O128:H-, O128:H2, O146:H8, O146:H21, O156:H-, and OUT:H21) were found more frequently in sheep. These observations suggest a host serotype specificity for some VTEC. Numerous bovine and ovine VTEC serotypes detected in Spain were associated with human illnesses, confirming that ruminants are important reservoirs of pathogenic VTEC. VTEC can produce one or two toxins (VT1 and VT2) that cause human illnesses. These toxins are different proteins encoded by different genes. Another virulence factor expressed by VTEC is the protein intimin that is responsible for intimate attachment of VTEC and effacing lesions in the intestinal mucosa. This virulence factor is encoded by the chromosomal gene eae. The eae gene was found at a much less frequency in bovine (17%) and ovine (5%) than in human (45%) non-O157 VTEC strains. This may support the evidence that the eae gene contributes significantly to the virulence of human VTEC strains and that many animal non-O157 VTEC strains are less pathogenic to humans.

Serotypes, virulence genes, and intimin types of Shiga toxin (verotoxin)-producing Escherichia coli isolates from healthy sheep in Spain

Fecal swabs obtained from 1,300 healthy lambs in 93 flocks in Spain in 1997 were examined for Shiga toxin-producing Escherichia coli (STEC). STEC O157:H7 strains were isolated from 5 (0.4%) animals in 4 flocks, and non-O157 STEC strains were isolated from 462 (36%) lambs in 63 flocks. A total of 384 ovine STEC strains were characterized in this study. PCR showed that 213 (55%) strains carried the stx(1) gene, 10 (3%) possessed the stx(2) gene, and 161 (42%) carried both the stx(1) and the stx(2) genes. Enterohemolysin (ehxA) and intimin (eae) virulence genes were detected in 106 (28%) and 23 (6%) of the STEC strains, respectively. The STEC strains belonged to 35 O serogroups and 64 O:H serotypes (including 18 new serotypes). However, 72% were of 1 of the following 12 serotypes: O5:H-, O6:H10, O91:H-, O117:H-, O128:H-, O128:H2, O136:H20, O146:H8, O146:H21, O156:H-, O166:H28, and ONT:H21 (where NT is nontypeable). Although the 384 STEC strains belonged to 95 different seropathotypes (associations between serotypes and virulence genes), 49% of strains belonged to only 11. O91:H- stx(1) stx(2) (54 strains) was the most common seropathotype, followed by O128:H- stx(1) stx(2) (33 strains) and O6:H10 stx(1) (25 strains). Three strains of serotypes O26:H11, O156:H11, and OX177:H11 had intimin type beta1; 5 strains of serotype O157:H7 possessed intimin type gamma1; and 15 strains of serotypes O49:H-, O52:H12, O156:H- (12 strains), and O156:H25 had the new intimin, intimin type zeta. The majority (82%) of ovine STEC strains belonged to serotypes previously found to be associated with human STEC strains, and 51% belonged to serotypes associated with STEC strains isolated from patients with hemolytic-uremic syndrome. Thus, this study confirms that healthy sheep are a major reservoir of STEC strains pathogenic for humans.

Host defences to Citrobacter rodentium

Citrobacter rodentium is a natural non-invasive bacterial pathogen which infects the distal colon of mice. It uses the same molecular mechanisms of type III secretion as human enteropathogenic and enterohemorrhagic Escherichia coli to colonise the epithelial cells of the gut and is therefore an ideal model to study host-bacterial pathogen interactions in vivo. Infection elicits mucosal inflammation with similarities to inflammatory bowel disease, and so it is a readily accessible model to investigate the relationship between inflammation and anti-bacterial immunity in the gut.

Distribution of the saa gene in strains of Shiga toxin-producing Escherichia coli of human and bovine origins

Certain strains of Shiga toxin-producing Escherichia coli (STEC) which do not have the locus of enterocyte effacement pathogenicity island carry the STEC autoagglutinating adhesin (saa) gene. The distribution of the saa gene in STEC isolates from patients with hemolytic-uremic syndrome (HUS), patients with less severe diarrheal disease, asymptomatic individuals, and healthy cattle was examined. saa-positive strains were detected more frequently (P < 0.001) in STEC strains from bovines (32 of 56 strains) than in those from humans (8 of 91 strains). No significant association (P = 0.135) was found between the saa gene and STEC isolated from patients with HUS (6 of 46 strains) or diarrhea (2 of 29 strains) and from healthy controls (0 of 16 strains).

Description of a novel intimin variant (type zeta) in the bovine O84:NM verotoxin-producing Escherichia coli strain 537/89 and the diagnostic value of intimin typing

Infections with verotoxin-producing Escherichia coli (VTEC) has resulted in increasing numbers of human illnesses annually. These illnesses usually result from the ability of VTEC to cause the attaching and effacing lesions (AE lesion). The AE phenotype is encoded by the locus of enterocyte effacement (LEE) pathogenicity island. A key adhesion factor involved is the outer membrane protein intimin, encoded by the eae gene within the LEE. Intimin types alpha, beta, gamma, delta, and epsilon have been described previously. Each intimin represents distinct phylogenetic lineages of LEE-positive strains. A new intimin type zeta was identified in a VTEC strain of the serotype O84:NM (nonmotile) that was isolated from a calf with diarrhea. zeta intimin showed the highest similarity (88%) of its amino acid sequence to the alpha intimin. For diagnostic purposes, we established a polymerase chain reaction (PCR) method for diagnosis of the key virulence traits of VTEC (i.e., verotoxins and intimins). This method also distinguishes between the toxins (VT1 and VT2) and the six intimin types. By applying the PCR method, intimin zeta in strains of other VTEC serotypes O84:H2, O92:NM, O119:H25, and O150:NM was identified. Because the intimin types represent distinctive phylogenetic E. coli lineages, application of the intimin subtyping PCR offers significant benefits. These include improving diagnosis of VTEC infection and increasing the understanding of evolution of attaching and effacing VTEC and other LEE-positive bacteria.

Characterization of monkey enteropathogenic Escherichia coli (EPEC) and human typical and atypical EPEC serotype isolates from neotropical nonhuman primates

Enteropathogenic Escherichia coli (EPEC) has been associated with infantile diarrhea and mortality in humans in developing countries. While diarrhea is also a major problem among primates kept in captivity, the role of E. coli is unclear. This study was designed to characterize diarrheagenic E. coli recovered from the feces of 56 New World nonhuman primates, primarily marmosets (Callithrix spp.). Seventeen of the 56 primates had signs of diarrhea and/or enteritis. E. coli recovered from feces from these animals was tested by PCR for genes encoding virulence factors of diarrheagenic E. coli and for patterns of adherence to HeLa cells. In addition, isolates were characterized by the fluorescence actin staining test and by their ability to induce attaching and effacing lesions. PCR for the eae gene was positive in 10 of the 39 (27%) apparently healthy animals and in 8 of the 17 (47%) animals with diarrhea and/or enteritis. Colonies of eae(+) E. coli were serotyped and examined by PCR for genes encoding EPEC virulence markers. The eae(+) E. coli isolates recovered from both healthy and sick nonhuman primates demonstrated virulence-associated attributes similar to those of EPEC strains implicated in human disease and are designated monkey EPEC. The results presented here indicate that EPEC may be a significant pathogen for nonhuman primates, deserving further investigation. The similarities between the affected animals investigated in this study and human EPEC infections suggest that marmosets may represent an important model for EPEC in humans.

Prevalence of the new, SPI1-like, pathogenicity island ETT2 among Escherichia coli

The new pathogenicity island ETT2 has been identified by PCR and gene probes among various intestinal serovars and pathovars of E. coli, in particular among EHEC/STEC. However, ETT2 was not detected among extra-intestinal and non-pathogenic E. coli strains or other enteric bacteria including various S. enterica serovars. A considerable molecular diversity of ETT2 among various E. coli serovars was found. The occurrence of ETT2 among E. coli is independent of the presence of other virulence properties, e.g. the pathogenicity islands LEE, LPA, or HPI.

Dissemination of pheU- and pheV-located genomic islands among enteropathogenic (EPEC) and enterohemorrhagic (EHEC) E. coli and their possible role in the horizontal transfer of the locus of enterocyte effacement (LEE)

We have recently shown that the locus of enterocyte effacement (LEE) of the bovine enterohemorrhagic E. coli RW1374 (O103:H2) resides within a large pathogenicity island (PAI), integrated in the vicinity of the phenylalanine tRNA gene pheV. Here we describe an additional, but LEE-negative genomic island in RW1374 in the vicinity of another phenylalanine tRNA gene, pheU, the sequence of which is identical to pheV. These two genomic islands revealed identity of the left, but a relative variability of their right end sequences. To investigate the mechanism of LEE-PAI distribution in E. coli, we analysed similar junctions in the pheU/pheV loci of additional EPEC and EHEC strains the LEE location of which had not been determined before. By hybridisation of NotI restriction fragments with probes specific for LEE, pheV locus, and pheU locus, the LEE was found linked to either one of these two loci. The results agreed well with recently published phylogenetic data and indicate that in the clones of diarrheagenic E. coli (Dec) Dec 11 and Dec 12, forming the phylogenetic cluster EPEC 2, and in the strains of the most typical serotypes of the Dec 8, belonging to the phylogenetic cluster EHEC 2, the LEE was linked with pheV and not with the pheU locus as previously assumed. Sequence comparison with other pheU- and pheV-located genomic islands from different E. coli pathotypes (uropathogenic E. coli, septicemic E. coli) as well as from Shigella indicated the same structural features at the junctions. These conserved structures suggested a common DNA cassette, serving as common vehicle for horizontal gene transfer of various PAls. In addition, the elements suggest an origin from a common pheU-located ancestor and integration into the chromosome through site-specific recombination. Our results indicate that pheU/pheV-located genomic islands played an important role in the evolution of several PAls in E. coli and related pathogens.

Human intestinal tissue tropism of intimin epsilon O103 Escherichia coli

Human intestinal in vitro organ culture was used to assess the tissue tropism of human isolates of Escherichia coli O103:H2 and O103:H- that express intimin epsilon. Both strains showed tropism for follicle associated epithelium and limited adhesion to other regions of the small and large intestine. This is similar to the tissue tropism shown by intimin gamma enterohaemorrhagic (EHEC) O157:H7, but distinct from that of intimin alpha enteropathogenic (EPEC) O127:H6.

Isolation from a sheep of an attaching and effacing Escherichia coli O115:H- with a novel combination of virulence factors

Attaching and effacing (AE) lesions were observed in the caecum, proximal colon and rectum of one of four lambs experimentally inoculated at 6 weeks of age with Escherichia coli O157:H7. However, the attached bacteria did not immunostain with O157-specific antiserum. Subsequent bacteriological analysis of samples from this animal yielded two E. coli O115:H(-) strains, one from the colon (CO) and one from the rectum (RC), and those bacteria forming the AE lesions were shown to be of the O115 serogroup by immunostaining. The O115:H(-)isolates formed microcolonies and attaching and effacing lesions, as demonstrated by the fluorescence actin staining test, on HEp-2 tissue culture cells. Both isolates were confirmed by PCR to encode the epsilon (epsilon) subtype of intimin. Supernates of both O115:H(-) isolates induced cytopathic effects on Vero cell monolayers, and PCR analysis verified that both isolates encoded EAST1, CNF1 and CNF2 toxins but not Shiga-like toxins. Both isolates harboured similar sized plasmids but PCR analysis indicated that only one of the O115:H(-) isolates (CO) possessed the plasmid-associated virulence determinants ehxA and etpD. Neither strain possessed the espP, katP or bfpA plasmid-associated virulence determinants. These E. coli O115:H(-) strains exhibited a novel combination of virulence determinants and are the first isolates found to possess both CNF1 and CNF2.

Genetic diversity of intimin genes of attaching and effacing Escherichia coli strains

In this study, we determined the sequences of four intimin variant genes detected in attaching and effacing Escherichia coli isolates of human origin. Three of them were novel and were designated eae-eta (eta), eae-iota (iota), and eae-kappa (kappa). The fourth was identical to the recently described eae-zeta (zeta), isolated from a bovine E. coli O84:NM isolate. We compared these sequences with those of published intimin-alpha, intimin-beta, intimin-gamma1, intimin-gamma2, intimin- epsilon, and intimin-theta alleles. Sequence analysis of these 10 intimin alleles confirmed extensive genetic diversity within the intimin gene family in E. coli. The genetic diversity was more prominent in the 3' region (starting at bp 2,112), which encodes the binding domain of intimin. Phylogenetic analyses revealed four groups of closely related intimin genes: alpha and zeta; beta and kappa; gamma1 and gamma2/theta; and epsilon and eta. Calculation of homoplasy ratios of sequences of the 5' region of eae (positions 1 to 2,111) revealed evidence for intragenic recombination. Split decomposition analysis also indicates that recombination events have played a role in the evolutionary history of eae. In conclusion, we recommend an eae nomenclature system based on the Greek alphabet and provide an updated PCR scheme for amplification and typing of E. coli eae.

A multiresistant clone of Shiga toxin-producing Escherichia coli O118:[H16] is spread in cattle and humans over different European countries

Multiresistant Shiga toxin-producing Escherichia coli (STEC) O118:H16 and O118 nonmotile strains (designated O118:[H16]) were detected by examination of 171 STEC isolates for their antimicrobial sensitivity. Of 48 STEC O118:[H16] strains, 98% were resistant to sulfonamide, 96% were resistant to streptomycin, 79% were resistant to kanamycin, 75% were resistant to tetracycline, 67% were resistant to ampicillin, 60% were resistant to chloramphenicol, 48% were resistant to trimethoprim, and 10% each were resistant to gentamicin and nalidixic acid. Nalidixic acid resistance and reduced susceptibility to ciprofloxacin were associated with the mutation gyrA(LEU-83). The STEC O118:[H16] strains were found to belong to a single genetic clone as investigated by multilocus enzyme electrophoresis and by multilocus sequence analysis of E. coli housekeeping genes. The STEC O118:[H16] strains originated from humans and cattle and were isolated in seven different countries of Europe between 1986 and 1999. Strains showing multiresistance to up to eight different antimicrobials predominated among the more recent STEC O118:[H16] strains. The genes in parentheses were associated with resistance to kanamycin (aphA1-Ia), chloramphenicol (catA1), tetracycline [tet(A)], and ampicillin (bla(TEM-1)). Class 1 integrons containing sulI (sulfonamide resistance), aadA1a (streptomycin resistance), or dfrA1 (trimethoprim resistance)-aadA1a gene cassettes were detected in 28 strains. The bla(TEM-1b) gene was present in 18 of 21 strains that were examined by nucleotide sequencing. Class 1 integrons and bla(TEM) genes were localized on plasmids and/or on the chromosome in different STEC O118:[H16] strains. Hybridization of XbaI-digested chromosomal DNA separated by pulsed-field gel electrophoresis revealed that bla(TEM) genes were integrated at different positions in the chromosome of STEC O118:[H16] strains that could have occurred by Tn2 insertion. Our data suggest that strains belonging to the STEC O118:[H16] clonal group have a characteristic propensity for acquisition and maintenance of resistance determinants, thus contrasting to STEC belonging to other serotypes.

Molecular characterization of a serotype O121:H19 clone, a distinct Shiga toxin-producing clone of pathogenic Escherichia coli

Most illnesses caused by Shiga toxin-producing Escherichia coli (STEC) have been attributed to E. coli serotype O157:H7, but non-O157 STEC infections are now increasingly recognized as public health problems worldwide. The O121:H19 serotype is being isolated more frequently from clinical specimens and has been implicated in one waterborne outbreak. We used multilocus virulence gene profiling, a PCR-based assay, to characterize the virulence gene content of 24 isolates of serotype O121:H19 and nonmotile variants. We also performed multilocus enzyme electrophoresis and multilocus sequencing to establish the clonal relatedness of O121 isolates and to elucidate the relationship of O121 to common STEC clones. The 24 isolates were found to represent a single bacterial clone, as there was no allelic variation across 18 enzyme loci among the isolates. The complete nucleotide sequence of the intimin gene differed by four substitutions from that of the epsilon (Int- epsilon ) allele of O103:H2 strain PMK5. The typical O121 virulence gene profile was similar to the profiles of enterohemorrhagic E. coli (EHEC) clones of E. coli: it included a Shiga toxin 2 gene (stx(2)), two genes on the EHEC plasmid (toxB and ehxA), and the gene encoding intimin (eae). Despite the similarities, putative virulence genes distributed on O islands-large chromosomal DNA segments present in the O157:H7 genome-were useful for discriminating among STEC serotypes and the O121:H19 clone had a composite profile that was distinct from the profiles of the other major EHEC clones of pathogenic E. coli. On the basis of sequencing analysis with 13 housekeeping genes, the O121:H19 clone did not fall into any of the four classical EHEC and enteropathogenic E. coli groups but instead was closely related to two eae-negative STEC strains.

Tyrosine residues at the immunoglobulin-C-type lectin inter-domain boundary of intimin are not involved in Tir-binding but implicated in colonisation of the host

Intimin is an outer membrane adhesion molecule involved in bacterial adhesion to intestinal epithelium by several human and animal enteric pathogens, including enteropathogenic and enterohaemorrhagic Escherichia coli and Citrobacter rodentium. Intimin binds to the translocated intimin receptor, Tir, which is delivered to the plasma membrane of the host cell by a type III protein translocation system. Intimin is also implicated in binding to a host cell-encoded intimin receptor (Hir). The receptor-binding activity of intimin resides within the carboxy terminus 280 amino acids (Int280) of the polypeptide. Structural analysis of this region revealed two immunoglobulin-like domains, the second of which forms a number of contacts with the distal C-type lectin-like module. Specific orientation differences at this inter-domain boundary, which consists of several tyrosine residues, were detected between the crystal and solution structures. In this study, we determined the influence of site-directed mutagenesis of each of four tyrosine residues on intimin-Tir interactions and on intimin-mediated intimate attachment. The mutant intimins were also studied using a variety of in vitro and in vivo infection models. The results show that three of the four Tyr, although not essential for A/E lesion formation in vitro, are required for efficient colonisation of the mouse host following oral challenge.

Prevalence and characteristics of intimin- and Shiga toxin-producing Escherichia coli from gulls, pigeons and broilers in Finland

The role of birds as sources of Shiga toxin-and intimin-producing Escherichia coli was studied. Fecal samples from live gulls (n=86), pigeons (n=33) and broiler chickens (n=199) from 23 flocks were analyzed for stx and eae by PCR. No stx positive samples were detected. In contrast, eae E. coli were highly prevalent among gulls (40%), and was also found in pigeons (7%) and chickens (57% of the flocks contaminated). The eae positive isolates were analyzed genetically and O-serogrouped. One isolate from a pigeon was found to have stx (2f). The isolates of gulls differed from those of pigeons and chickens, and all eae E. coli isolates from birds differed from human pathogenic strains by the lack of EHEC-hlyA and bfp/EAF as well as distribution of O-serogroups. Thus, birds cannot be regarded as important carriers of zoonotic stx or eae E. coli in Finland.

Serobiotypes and virulence genes of Escherichia coli strains isolated from diarrheic and healthy rabbits in Brazil

A total of 178 Escherichia coli isolates from diarrheic and healthy rabbits in the São Paulo State (Brazil) were serobiotyped and investigated by PCR for the presence of virulence genes. Among the 90 (50.6%) isolates which possessed the eae gene, 74 were from diarrheic animals and all but one encoded intimin beta. Sixty five (72.2%) of the eae+ isolates had insertion of the locus of enterocyte effacement locus in the pheU locus, 11 (12.2%) in the selC and 14 (15.6%) did not insert in either of these loci. All isolates were negative for genes of the E. coli enterotoxins, Stx1, Stx2, CNF1, CNF2 and EHEC hemolysin. The O132:H2 serotype was dominant, being present in 63 isolates (70%) of the 90 eae+ isolates, and 57 of the 63 isolates of this serotype belonged to biotype 30. PCR detected the gene for AF/R2 fimbriae in 75 (83.3%) of the 90 eae+ isolates. Adherence to HeLa cells was best detected following 6h incubation and a positive fluorescence actin staining (FAS) test was given by 52 isolates. These data show that isolates of E. coli associated with diarrhea in rabbits in Brazil possess the genotype and phenotype typically associated with rabbit enteropathogenic E. coli (EPEC). We conclude that EPEC that possess the eae gene are a common cause of diarrhea in Brazilian rabbit farms and that the pathogenic eae+ AF/R2+ isolates of O132:H2:B30 serobiotype are especially predominant.

Multiplex fluorogenic real-time PCR for detection and quantification of Escherichia coli O157:H7 in dairy wastewater wetlands

Surface water and groundwater are continuously used as sources of drinking water in many metropolitan areas of the United States. The quality of water from these sources may be reduced due to increases in contaminants such as Escherichia coli from urban and agricultural runoffs. In this study, a multiplex fluorogenic PCR assay was used to quantify E. coli O157:H7 in soil, manure, cow and calf feces, and dairy wastewater in an artificial wetland. Primers and probes were designed to amplify and quantify the Shiga-like toxin 1 (stx1) and 2 (stx2) genes and the intimin (eae) gene of E. coli O157:H7 in a single reaction. Primer specificity was confirmed with DNA from 33 E. coli O157:H7 and related strains with and without the three genes. A direct correlation was determined between the fluorescence threshold cycle (C(T)) and the starting quantity of E. coli O157:H7 DNA. A similar correlation was observed between the C(T) and number of CFU per milliliter used in the PCR assay. A detection limit of 7.9 x 10(-5) pg of E. coli O157:H7 DNA ml(-1) equivalent to approximately 6.4 x 10(3) CFU of E. coli O157:H7 ml(-1) based on plate counts was determined. Quantification of E. coli O157:H7 in soil, manure, feces, and wastewater was possible when cell numbers were >/=3.5 x 10(4) CFU g(-1). E. coli O157:H7 levels detected in wetland samples decreased by about 2 logs between wetland influents and effluents. The detection limit of the assay in soil was improved to less than 10 CFU g(-1) with a 16-h enrichment. These results indicate that the developed PCR assay is suitable for quantitative determination of E. coli O157:H7 in environmental samples and represents a considerable advancement in pathogen quantification in different ecosystems.

Development of a capture ELISA for the detection of antibodies to enteropathogenic Escherichia coli (EPEC) in rabbit flocks using intimin-specific monoclonal antibodies

A capture enzyme-linked immunosorbent assay (cELISA) was developed using intimin-specific monoclonal antibodies to detect specific antibody in rabbits that have been in contact with enteropathogenic Escherichia coli (EPEC). Sera from 121 EPEC-negative, minimum-disease-level (MDL) rabbits were used for negative controls, and sera from 25 MDL rabbits, experimentally infected with EPEC of bio-/serotype 3-/O15, for positive controls. These were used to determine a cut-off value for a positive cELISA result. The value selected gave the test a sensitivity of 80.0% and a specificity of 98.4% on an individual level. At this value, a flock level sensitivity and specificity of 79.2 and 85.2%, respectively were calculated for a flock with a prevalence of seven per cent, if 40 animals were tested, and a minimum of two reactors were obtained. The test characteristics improve with increasing prevalence. To evaluate the diagnostic potential of the cELISA, sera from 40 to 50 slaughter rabbits per flock from 25 rabbit flocks with bacteriologically determined EPEC status were tested. The results demonstrated that this test can be a useful tool to determine the EPEC status of a rabbitry, provided that it is used at regular intervals.

Characterisation of Escherichia coli O157 isolates from Danish cattle and human patients by genotyping and presence and variants of virulence genes

Escherichia coli O157 isolates obtained from 17 Danish cattle herds and from a national surveillance programme of cattle at slaughter were genotyped by pulsed-field gel electrophoresis (PFGE) and characterised with respect to presence of and variation in virulence factors. The characteristics of the cattle strains were compared to human clinical isolates from the same time period. All verocytotoxin (VT)-producing E. coli O157 (VTEC O157) from cattle possessed all typical VTEC O157:H7 virulence factors and had either the VT2c-variant alone or together with VT1. Among human isolates the dominant toxin profile was VT2 + VT2c. Only one PFGE group was represented on each farm, indicating that introduction and establishment of new E. coli O157 strains to these cattle farms is probably not common. Among E. coli O157 isolates from cattle, 22.8% were not VT-producing. The majority of these possessed the eae gene and all other genotypic and phenotypic traits typical for E. coli O157:H7. On the basis of the virulence characteristics, it is concluded that the VTEC O157 strains isolated from Danish cattle are potential human pathogens. However, the observed differences between cattle and human isolates with regard to VT-profile, genotype and antimicrobial resistance could be important, i.e. either Danish cattle might not be the most important reservoir for human infections or Danish cattle mostly harbour VTEC O157 isolates that are less likely to cause human disease.

Consequences of EHEC colonisation in humans and cattle

While many factors have been associated with human EHEC infection, the full role these play in both human and ruminant hosts are not yet clear despite much investigation. It is hoped that the continued intense international research effort into EHEC will provide further insights into the commensal versus pathogenic lifestyles of E. coli and lead to approaches to reduce EHEC carriage in ruminants as well as prevent or treat human disease.

Tissue tropism of enteropathogenic Escherichia coli strains belonging to the O55 serogroup

Four enteropathogenic Escherichia coli (EPEC) strains belonging to the O55 serogroup (G21 and G30 [both O55:H6], G35 [O55:H-], and G58 [O55:H7]) were tested for their tissue tropism by using human intestinal in vitro organ culture. Strains showed restricted adhesion with attaching-and-effacing activity to follicle-associated epithelium of Peyer's patches, with no apparent adhesion to duodenum or colon. G35 and G58 express intimin gamma and show a similar tropism to intimin gamma-expressing enterohemorrhagic E. coli (EHEC) O157:H7. However, strains G21 and G30 were unusual because they expressed intimin alpha and had a restricted tissue tropism of intimin gamma phenotype. The amino acid sequence of the carboxy-terminal 280 amino acids of intimin from G21 was determined. Comparison with the prototype intimin alpha from strain E2348/69 (O127:H6) showed a single amino acid difference (corresponding to Val907 and Ala907 in the whole intimins). This mutation was reproduced by site-directed mutagenesis in an intimin alpha plasmid template, pCVD438, with the hypothesis that it may induce a change in tropism. However, when the mutated plasmid was placed in both EPEC and EHEC backgrounds, duodenal adhesion in a manner similar to strain E2348/69 was evident upon in vitro organ culture. Thus, additional factor(s) unrelated to intimin exist in the O55:H6 genome that influence human intestinal tissue tropism.

[Transplantation of hematopoietic stem cells from umbilical cord blood]

Umbilical cord blood transplantation has many potential advantages over Bone Marrow Transplantation using other donor sources to patients in need of allogeneic hematopoietic stem cell transplantation. Collecting of Umbilical cord blood is a technically simple procedure that poses no foreseeable health risks to the mother or the fetus. The results achieved during the last 10 years of the European Transplantation Centers define this new technology as vanguard and perspective, alternative treatment of the patients obtained oncological disorders.

Clonal diversity of Shiga toxin-producing Escherichia coli O103:H2/H(-) in Germany

Shiga toxin producing Escherichia coli O103:H2/H(-) belong to the third most frequently isolated EHEC serotypes in Germany following isolates of O157:H7/H(-) and O26:H11/H(-). A total of 145 respective E. coli 103 isolates from single cases of diarrhoea and haemolytic uremic syndrome (HUS) in 1997-2000 were characterised by a range of molecular subtyping methods (PFGE, P-gene profiling, ribotyping, electrotyping) and phage typing in order to analyse their genetic relatedness and the practicability for new epidemiological tracing back. All isolates cluster into a distinct EHEC subgroup and reveal a high clonal diversity together with a considerable stability. Since strains of this serotype rank up to the third most frequently isolated EHEC in Germany a large population of this serotype, and therefore, a great supply of such strains may exist in this country.

Real-time fluorescence PCR assays for detection and characterization of Shiga toxin, intimin, and enterohemolysin genes from Shiga toxin-producing Escherichia coli

PCR assays have proved useful for detecting and characterizing Shiga toxin-producing Escherichia coli (STEC). Recent advances in PCR technology have facilitated the development of real-time fluorescence PCR assays with greatly reduced amplification times and improved methods for the detection of amplified target sequences. We developed and evaluated two such assays for the LightCycler instrument: one that simultaneously detects the genes for Shiga toxins 1 and 2 (stx(1) and stx(2)) and another that simultaneously detects the genes for intimin (eae) and enterohemolysin (E-hly). Amplification and sequence-specific detection of the two target genes were completed within 60 min. Findings from the testing of 431 STEC isolates of human and animal origin, 73 isolates of E. coli negative for stx genes, and 118 isolates of other bacterial species with the LightCycler PCR (LC-PCR) assays were compared with those obtained by conventional block cycler PCR analysis. The sensitivities and specificities of the LC-PCR assays were each 100% for the stx(1), eae, and E-hly genes and 96 and 100%, respectively, for the stx(2) gene. No stx(2) genes were detected from 10 stx(2f)-positive isolates because of significant nucleotide differences in their primer annealing regions. Melting curve analyses of the amplified Shiga toxin genes revealed sequence variation within each of the tested genes that correlated with described and novel gene variants. The performance characteristics of the LC-PCR assays, such as their speed, detection method, and the potential subtyping information available from melting curve analyses, make them attractive alternatives to block cycler PCR assays for detecting and characterizing STEC strains.

Identification of Escherichia coli O157:H7-strains from pigs with postweaning diarrhoea and amplification of their virulence marker genes by PCR

Escherichia coli isolated from pigs with postweaning diarrhoea were examined by PCR for the presence of the O157 rfb gene responsible for the biosynthesis of E coli O157 lipopolysaccharide. Among the 372 isolates tested, 38 (10.2 per cent) were of the O157 serogroup, but none of these possessed the H7 determinant. Further analysis of the E coli O157 isolates revealed that seven of them had the genes responsible for the production of Shiga toxin 1 and eaeA intimin, four other strains had genes responsible for the production of Shiga toxin 2, and four other strains were positive for the enterohaemolysin gene.

Antibiotic resistance, virulence gene, and molecular profiles of Shiga toxin-producing Escherichia coli isolates from diverse sources in Calcutta, India

Antibiotic resistance, virulence gene, and molecular profiles of Shiga toxin-producing Escherichia coli (STEC) non-O157 strains isolated from human stool samples, cow stool samples, and beef samples over a period of 2 years in Calcutta, India, were determined. Resistance to one or more antibiotics was observed in 49.2% of the STEC strains, with some of the strains exhibiting multidrug resistance. The dominant combinations of virulence genes present in the strains studied were stx(1) and stx(2) (44.5% of strains) and stx(1), stx(2), and hlyA (enterohemorrhagic E. coli hemolysin gene) (19% of strains). Only 6.4% of the STEC strains harbored eae. The diversity of STEC strains from various sources was assessed by random amplification of polymorphic DNA (RAPD). STEC strains that gave identical or nearly similar DNA fingerprints in RAPD-PCR and had similar virulence genotypes were further characterized by pulsed-field gel electrophoresis (PFGE). Identical RAPD and PFGE profiles were observed in four sets of strains, with each set comprising two strains. There was no match in the RAPD and PFGE profiles between strains of STEC isolated from cows and those isolated from humans. It appears that the clones present in bovine sources are not transmitted to humans in the Calcutta setting although these strains showed evolutionary relatedness. Maybe for this reason, STEC has still not become a major problem in India.

Mutagenesis of conserved tryptophan residues within the receptor-binding domain of intimin: influence on binding activity and virulence

Intimate bacterial adhesion to intestinal epithelium is a pathogenic mechanism shared by several human and animal enteric pathogens, including enteropathogenic and enterohaemorrhagic Escherichia coli and Citrobacter rodentium. The proteins directly involved in this process are the outer-membrane adhesion molecule intimin and the translocated intimin receptor, Tir. The receptor-binding activity of intimin resides within the carboxy terminus 280 aa (Int280) of the polypeptide. Four tryptophan residues, W117/776, W136/795, W222/881 and W240/899, are conserved within different Int280 molecules that otherwise show considerable sequence variation. In this study the influence of site-directed mutagenesis of each of the four tryptophan residues on intimin-Tir interactions and on intimin-mediated intimate attachment was determined. The mutant intimins were also studied using a variety of in vitro and in vivo infection models. The results show that all the substitutions modulated intimin activity, although some mutations had more profound effects than others.

Intimin type influences the site of human intestinal mucosal colonisation by enterohaemorrhagic Escherichia coli O157:H7

BACKGROUND

Enterohaemorrhagic (EHEC) and enteropathogenic (EPEC) Escherichia coli epithelial cell adhesion is characterised by intimate attachment, and attaching and effacing (A/E) lesion formation. This event is mediated in part by intimin binding to another bacterial protein, Tir (translocated intimin receptor), which is exported by the bacteria and integrated into the host cell plasma membrane. Importantly, EPEC (O127:H6) and EHEC (O157:H7) express antigenically distinct intimin types known as intimin alpha and gamma, respectively. EHEC (O157:H7) colonises human intestinal explants although adhesion is restricted to the follicle associated epithelium of Peyer's patches. This phenotype is also observed with EPEC O127:H6 engineered to express EHEC intimin gamma.

AIMS

To investigate the influence of intimin on colonisation of human intestine by E coli O157:H7, and intimin types on tissue tropism in humans.

METHODS

Human intestinal in vitro organ culture with wild type and mutant strains of O157:H7 were employed.

RESULTS

Introducing a deletion mutation in the eae gene encoding intimin gamma in EHEC (O157:H7) caused the strain (ICC170) to fail to colonise human intestinal explants. However, colonisation of Peyer's patches and A/E lesion formation were restored with intimin gamma expression from a plasmid (ICC170 (pICC55)). In contrast, complementing the mutation with intimin alpha resulted in a strain (ICC170 (pCVD438)) capable of colonising and producing A/E lesions on both Peyer's patch and other small intestinal explants.

CONCLUSION

Intimin is necessary for human intestinal mucosal colonisation by E coli O157:H7. Intimin type influences the site of colonisation in a Tir type independent mechanism; intimin gamma appears to restrict colonisation to human follicle associated epithelium.

Intimin, tir, and shiga toxin 1 do not influence enteropathogenic responses to shiga toxin-producing Escherichia coli in bovine ligated intestinal loops

Shiga toxin-producing Escherchia coli (STEC) comprises a group of attaching and effacing (A/E) enteric pathogens of animals and humans. Natural and experimental infection of calves with STEC may result in acute enteritis or subclinical infection, depending on serotype- and host-specific factors. To quantify intestinal secretory and inflammatory responses to STEC in the bovine intestine, serotypes that are associated with human disease (O103:H2 and O157:H7) were introduced into ligated mid-ileal loops in gnotobiotic and conventional calves, and fluid accumulation and recruitment of radiolabeled neutrophils were measured after 12 h. STEC serotype O103:H2, but not serotype O157:H7, elicited strong enteropathogenic responses. To determine if the inflammatory response to STEC O103:H2 in calves requires Shiga toxin 1 or intimate bacterial attachment to the intestinal epithelium, defined mutations were made in the stx1, eae, and tir genes. Our data indicate that some STEC induce intestinal inflammatory responses in calves by a mechanism that is independent of A/E-lesion formation, intimin, or Shiga toxin 1. This may have implications for strategies to reduce STEC carriage in cattle.

Cell surface-localized nucleolin is a eukaryotic receptor for the adhesin intimin-gamma of enterohemorrhagic Escherichia coli O157:H7

Intimin-gamma is an outer membrane protein of enterohemorrhagic Escherichia coli (EHEC) O157:H7 that is required for the organism to adhere tightly to HEp-2 cells and to colonize experimental animals. Another EHEC O157:H7 protein, the Transferred intimin receptor (Tir), is considered the primary receptor for intimin-gamma. Nevertheless, Tir-independent binding of intimin-gamma to HEp-2 cells has been reported. This observation suggests the existence of a eukaryotic receptor(s) for intimin-gamma. In this study, we sought to identify that receptor(s). First, we determined by equilibrium binding titration that the association of purified intimin-gamma with HEp-2 cells was specific and consistent with a single host cell receptor. Second, we isolated a protein from lysates of HEp-2 cells that bound intimin-gamma and subsequently identified this molecule as nucleolin, a protein involved in cell growth regulation that can be cell surface-expressed. Third, we established that purified intimin-gamma and nucleolin were co-localized on the surface of HEp-2 cells and that the site of EHEC O157:H7 attachment was associated with regions of nucleolin expression. Finally, we demonstrated that mouse anti-nucleolin sera significantly decreased the adherence of EHEC O157:H7 to HEp-2 cells. From this, we conclude that nucleolin is the HEp-2 cell receptor for intimin-gamma expressed by EHEC O157:H7.

Examination of Escherichia coli from poultry for selected adhesin genes important in disease caused by mammalian pathogenic E. coli

A collection of 1601 extraintestinal and intestinal Escherichia coli isolated from chickens, turkeys and ducks, in Belgium, France and Spain, was hybridised with gene probes specific for fimbrial and afimbrial adhesins (F17, F18, S <Sfa/F1C>, Bfp, Afa, Cs31A, Intimin <Eae>, Aida-1) of intestinal, urinary and invasive E. coli of mammals and with a probe specific for the P (Pap/Prs) fimbrial adhesin of urinary and invasive E. coli of mammals and birds. Three hundred and eighty-three strains (23.9%) were P-positive, 76 strains (4.8%) were Afa-positive, 75 strains (4.7%) were F17-positive, 67 strains (4.2%) were S-positive, 23 (1.4%) were Intimin-positive, and all were F18-, Cs31A-, Aida1- and Bfp-negative. The 75 F17-positive strains harboured different major subunit A-encoding gene variants, but the f17Ac variant was the most frequent (52 strains, 69.3%) and seven strains (9.3%) were not typeable. The f17G gene variant coding for the GII adhesin was the most frequent (56 strains, 75.0%), whereas the f17GI gene variant was present in four strains (5%) and 15 strains (20.0%) were not typeable. All Afa-positive strains harboured the afa-8 variant. The 23 Intimin-positive E. coli tested positive for the beta-variant (16 strains; 69.6%) or for the gamma-variant (seven strains; 30.4%) of the eae gene. Chicken and turkey E. coli were more frequently probe-positive (43.6 and 43.1%, respectively) than duck E. coli (31.5%) and extraintestinal E. coli were also more frequently probe-positive (48.4%) than intestinal strains (18.5%). Different combinations of probe positive hybridisation results were observed in 72 of the 540 probe-positive E. coli (13.3%). The most frequent combinations were between AfaE-8 and F17 probes (47 strains; 8.7%) and between P and S probes (13 strains; 2.4%). Although f17- and afa-8-related DNA sequences can be plasmid-located in mammalian E. coli, they were not in avian E. coli. Besides the P fimbrial adhesins, F17 and S fimbrial and Afa-VIII and Intimin afimbrial adhesins may thus represent colonisation factors of avian pathogenic E. coli.

Immunological characterization of Escherichia coli O157:H7 intimin gamma1

Portions of the intimin genes of Escherichia coli O157:H7 strain E319 and of the enteropathogenic E. coli O127:H6 strain E2348/69 were amplified by PCR and cloned into pET-28a+ expression vectors. The entire 934 amino acids (aa) of E. coli O157:H7 intimin, the C-terminal 306 aa of E. coli O157:H7 intimin, and the C-terminal 311 aa of E. coli O127:H6 intimin were expressed as proteins fused with a six-histidine residue tag (six-His tag) in pET-28a+. Rabbit antisera raised against the six-His tag-full-length E. coli O157:H7 intimin protein fusion cross-reacted in slot and Western blots with outer membrane protein preparations from the majority of enterohemorrhagic and enteropathogenic E. coli serotypes which have the intimin gene. The E. coli strains tested included isolates from humans and animals which produce intimin types alpha (O serogroups 86, 127, and 142), beta1 (O serogroups 5, 26, 46, 69, 111, 126, and 128), gamma 1 (O serogroups 55, 145, and 157), gamma 2 (O serogroups 111 and 103), and epsilon (O serogroup 103) and a nontypeable intimin (O serogroup 80), results based on intimin type-specific PCR assays. Rabbit antisera raised against the E. coli O157:H7 C-terminal fusion protein were much more intimin type-specific than those raised against the full-length intimin fusion protein, but some cross-reaction with other intimin types was also observed for these antisera. In contrast, the monoclonal antibody Intgamma1.C11, raised against the C-terminal E. coli O157 intimin, reacted only with preparations from intimin gamma 1-producing E. coli strains such as E. coli O157:H7.

Display of passenger proteins on the surface of Escherichia coli K-12 by the enterohemorrhagic E. coli intimin EaeA

Intimins are members of a family of bacterial adhesins from pathogenic Escherichia coli which specifically interact with diverse eukaryotic cell surface receptors. The EaeA intimin from enterohemorrhagic E. coli O157:H7 contains an N-terminal transporter domain, which resides in the bacterial outer membrane and promotes the translocation of four C-terminally attached passenger domains across the bacterial cell envelope. We investigated whether truncated EaeA intimin lacking two carboxy-terminal domains could be used as a translocator for heterologous passenger proteins. We found that a variant of the trypsin inhibitor Ecballium elaterium trypsin inhibitor II (EETI-II), interleukin 4, and the Bence-Jones protein REI(v) were displayed on the surface of E. coli K-12 via fusion to truncated intimin. Fusion protein net accumulation in the outer membrane could be regulated over a broad range by varying the cellular amount of suppressor tRNA that is necessary for translational readthrough at an amber codon residing within the truncated eaeA gene. Intimin-mediated adhesion of the bacterial cells to eukaryotic target cells could be mimicked by surface display of a short fibrinogen receptor binding peptide containing an arginine-glycine-aspartic acid sequence motif, which promoted binding of E. coli K-12 to human platelets. Cells displaying a particular epitope sequence fused to truncated intimin could be enriched 200,000-fold by immunofluorescence staining and fluorescence-activated cell sorting in three sorting rounds. These results demonstrate that truncated intimin can be used as an anchor protein that mediates the translocation of various passenger proteins through the cytoplasmic and outer membranes of E. coli and their exposure on the cell surface. Intimin display may prove a useful tool for future protein translocation studies with interesting biological and biotechnological ramifications.

Organisation and in vitro expression of esp genes of the LEE (locus of enterocyte effacement) of bovine enteropathogenic and enterohemorrhagic Escherichia coli

Enteropathogenic (EPEC) and enterohemorrhagic (EHEC) Escherichia coli infections are characterised by the formation of attaching and effacing (AE) lesions on intestinal epithelial cells. Secretion of extracellular proteins (EspA, EspB, and EspD) via a type III secretion apparatus is necessary for the formation of the AE lesions by human EPEC. In this study, we show that bovine EPEC and EHEC are also able to secrete polypeptides homologous to the already described Esp proteins, most probably via a type III secretion system. Bovine EPEC and EHEC strains present two different secretion profiles of Esp proteins which correlate to the pathotypes of the esp genes as determined by PCR. We also demonstrate that genes encoding secreted proteins, present in the LEE of two bovine strains, are organised in the same way as in the human EPEC strain E2348/69.

A novel locus of enterocyte effacement (LEE) pathogenicity island inserted at pheV in bovine Shiga toxin-producing Escherichia coli strain O103:H2

We describe a locus of enterocyte effacement (LEE) which is part of a new pathogenicity island (PAI) detected in the bovine Shiga toxin-producing Escherichia coli strain RW1374 (O103:H2). This PAI is at least 80 kb in size and inserted in the vicinity of the pheV tRNA gene at 67 min of the E. coli chromosome. Furthermore, the PAI differs from the previously described LEEs by unique flanking regions at both sides, which harbor one copy each of an insertion element in an inverted orientation that is 96% identical to insertion site (IS)629. In addition, a 5-kb PAI-specific sequence downstream of the LEE core region and adjacent to the E. coli K12 region is duplicated upstream of the LEE core region as well. The duplicated sequences are more than 80% identical to each other and consist partially of prophage sequences.

Locus of enterocyte effacement from Citrobacter rodentium: sequence analysis and evidence for horizontal transfer among attaching and effacing pathogens

The family of attaching and effacing (A/E) bacterial pathogens, which includes diarrheagenic enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC), remains a significant threat to human and animal health. These bacteria intimately attach to host intestinal cells, causing the effacement of brush border microvilli. The genes responsible for this phenotype are encoded in a pathogenicity island called the locus of enterocyte effacement (LEE). Citrobacter rodentium is the only known murine A/E pathogen and serves as a small animal model for EPEC and EHEC infections. Here we report the full DNA sequence of C. rodentium LEE and provide a comparative analysis with the published LEEs from EPEC, EHEC, and the rabbit diarrheagenic E. coli strain RDEC-1. Although C. rodentium LEE shows high similarities throughout the entire sequence and shares all 41 open reading frames with the LEE from EPEC, EHEC, and RDEC-1, it is unique in its location of the rorf1 and rorf2/espG genes and the presence of several insertion sequences (IS) and IS remnants. The LEE of EPEC and EHEC is inserted into the selC tRNA gene. In contrast, the Citrobacter LEE is flanked on one side by an operon encoding an ABC transport system, and an IS element and sequences homologous to Shigella plasmid R100 and EHEC pO157 flank the other. The presence of plasmid sequences next to C. rodentium LEE suggests that the prototype LEE resided on a horizontally transferable plasmid. Additional sequence analysis reveals that the 3-kb plasmid in C. rodentium is nearly identical to p9705 in EHEC O157:H7, suggesting that horizontal plasmid transfer among A/E pathogens has occurred. Our results indicate that the LEE has been acquired by C. rodentium and A/E E. coli strains independently during evolution.

Intimate interactions of enteropathogenic Escherichia coli at the host cell surface

Unlike many gastrointestinal pathogens, enteropathogenic Escherichia coli orchestrates the modulation of host cellular and immune responses from the exterior of the infected cell, chiefly via the secreted and translocated components of a type III secretion system. Close inspection of these enteropathogenic Escherichia coli proteins and the interactions they mediate provides an increasingly coherent picture of the pathogenic mechanisms that enteropathogenic Escherichia coli uses to exploit its host.

Intimin-specific immune responses prevent bacterial colonization by the attaching-effacing pathogen Citrobacter rodentium

The formation of attaching and effacing (A/E) lesions on gut enterocytes is central to the pathogenesis of enterohemorrhagic (EHEC) Escherichia coli, enteropathogenic E. coli (EPEC), and the rodent pathogen Citrobacter rodentium. Genes encoding A/E lesion formation map to a chromosomal pathogenicity island termed the locus of enterocyte effacement (LEE). Here we show that the LEE-encoded proteins EspA, EspB, Tir, and intimin are the targets of long-lived humoral immune responses in C. rodentium-infected mice. Mice infected with C. rodentium developed robust acquired immunity and were resistant to reinfection with wild-type C. rodentium or a C. rodentium derivative, DBS255(pCVD438), which expressed intimin derived from EPEC strain E2348/69. The receptor-binding domain of intimin polypeptides is located within the carboxy-terminal 280 amino acids (Int280). Mucosal and systemic vaccination regimens using enterotoxin-based adjuvants were employed to elicit immune responses to recombinant Int280alpha from EPEC strain E2348/69. Mice vaccinated subcutaneously with Int280alpha, in the absence of adjuvant, were significantly more resistant to oral challenge with DBS255(pCVD438) but not with wild-type C. rodentium. This type-specific immunity could not be overcome by employing an exposed, highly conserved domain of intimin (Int388-667) as a vaccine. These results show that anti-intimin immune responses can modulate the outcome of a C. rodentium infection and support the use of intimin as a component of a type-specific EPEC or EHEC vaccine.

Association between intimin (eae) and EspB gene subtypes in attaching and effacing Escherichia coli strains isolated from diarrhoeic lambs and goat kids

Attaching and effacing Escherichia coli (AEEC) strains isolated from diarrhoeic lambs and goat kids were characterized for intimin (eae) and EspB (espB) gene subtypes by PCR and sequencing, and for genetic relatedness by PFGE. Fifty (23 ovine and 27 caprine) AEEC strains of 398 (246 ovine and 152 caprine) analysed were detected by colony blot hybridization. These strains were epidemiologically unrelated since they were isolated from different outbreaks of neonatal diarrhoea over a long period. Ovine AEEC strains belonged to serogroups O2, O4, O26, O80, O91 or were untypable, and caprine strains belonged to serogroups O3, O153 and O163. Two intimin subtypes were detected among the ovine and caprine strains studied. Most of the strains (43/50) had the beta type intimin gene, but seven ovine strains possessed a variant gamma type intimin gene (gamma(V)). Analysis of deduced amino acid sequences of the eae gene revealed that the sequences of beta intimin of ovine and caprine strains were virtually identical to those of beta intimin of rabbit EPEC, human EPEC clone 2 and swine AEEC, whereas the gamma(V) intimin present in seven ovine strains had 75-76% identity with gamma intimin of human EHEC clone 1 strains, and 96% of identity with intimin of the human EHEC strain 95NR1 of serotype O111:H-. A PCR test was developed to identify the three different espB gene subtypes, espB of human EPEC clone 1 (espBalpha), espB of human EHEC clone 1 (espBgamma) and espB of rabbit EPEC and human EPEC clone 2 (espBbeta). There was close correlation between the intimin beta type and the espBbeta gene subtype in the ovine and caprine AEEC strains. The seven ovine strains possessing the gamma(V) intimin gene possessed the espBalpha gene subtype. None of the strains studied possessed the espBgamma gene found in human O157:H7 EHEC strains. PFGE analysis of genomic DNA of selected strains showed a great diversity among strains. Cluster analysis of PFGE patterns showed greater divergence between strains with the gamma(V) intimin gene than between strains with the beta intimin gene. This study showed that most of the AEEC strains isolated from diarrhoeic lambs and goat kids possessed beta intimin and espB genes identical to those of rabbit EPEC, and they may be associated with enteric disease in small ruminants.