Cytolethal distending toxin gene cluster in enterohemorrhagic Escherichia coli O157:H- and O157:H7: characterization and evolutionary considerations

We identified a cytolethal distending toxin (cdt) gene cluster in 87, 6, and 0% of sorbitol-fermenting (SF) enterohemorrhagic Escherichia coli (EHEC) O157:H(-), EHEC O157:H7, and E. coli O55:H7/H(-) strains, respectively. The toxin was expressed by the wild-type EHEC O157 strains and by a cdt-containing cosmid from a library of SF EHEC O157:H(-) strain 493/89. The cdt flanks in strain 493/89 were homologous to bacteriophages P2 and lambda. Our data demonstrate that cdt, encoding a potential virulence factor, is present in the EHEC O157 complex and suggest that cdt may have been acquired by phage transduction.     

Characterization of an RTX toxin from enterohemorrhagic Escherichia coli O157:H7.

A hemolytic determinant of enterohemorrhagic Escherichia coli O157:H7 is encoded on a 90-kbp plasmid (pO157). This enterohemorrhagic E. coli toxin (Ehx) is a newly described RTX cytotoxin. The prototype RTX toxin is the E. coli hemolysin (Hly) associated with extraintestinal E. coli infections. We expressed Ehx from E. coli K-12 strains harboring either pSK3, a pO157 derivative marked with Tn801 unlinked to Ehx, or a recombinant plasmid containing an 11.9-kbp subclone (pEO40) of pSK3. The Ehx activities and antibody reactivities were compared with those of Hly. Little Ehx was secreted extracellularly from the strain harboring pSK3; however, when the Hly transport genes hlyBD were supplied in trans, both intracellular and extracellular levels of Ehx were enhanced more than 15-fold. The strain harboring pEO40 secreted at least 140-fold more Ehx than did the strain harboring pSK3, and neither intracellular nor extracellular levels were significantly enhanced by the addition of hlyBD in trans. Polyclonal anti-HlyA antiserum and several anti-HlyA monoclonal antibodies, including the monoclonal antibody A10, which is panreactive for nearly all RTX toxins, reacted with EhxA antigen by immunoblot analysis. In hemolysis and 51Cr release assays, Ehx demonstrated similar efficiencies in lysis of BL-3 cells (cells from a bovine lymphoma cell line) and sheep and human erythrocytes. Surprisingly, it demonstrated very little activity against two human lymphoma cell lines. In contrast, Hly lysed all five cell types tested, each to a greater extent than that demonstrated by comparable amounts of Ehx. As with other RTX toxins, Ehx activity was calcium dependent and heat labile.     

toxB gene on pO157 of enterohemorrhagic Escherichia coli O157:H7 is required for full epithelial cell adherence phenotype

Adherence of enterohemorrhagic Escherichia coli (EHEC) to the intestinal epithelium is critical for initiation of a bacterial infection. An in vitro infection study previously indicated that EHEC bacteria initially adhere diffusely and then proliferate to develop MC, a process that is mediated by various secreted proteins, such as EspA, EspB, EspD, Tir, and intimin, as well as other putative adherence factors. In the present study, we investigated the role of a large 93-kb plasmid (pO157) in the adherence of O157:H7 (O157Sakai) and found the toxB gene to be involved in the full adherence phenotype. A pO157-cured strain of O157Sakai (O157Cu) developed microcolonies on Caco-2 cells; however, the number of microcolonies was lower than that of O157Sakai, as were the production and secretion levels of EspA, EspB, and Tir. Introduction of a mini-pO157 plasmid (pIC37) composed of the toxB and ori regions restored full adherence capacity to O157Cu, including production and secretion of the proteins. In contrast, introduction of a pO157 mutant possessing toxB::Km into O157Cu could not restore the full adherence phenotype. Expression of truncated versions of His-tagged ToxB also promoted EspB production and/or secretion by O157Cu. These results suggest that ToxB contributes to the adherence of EHEC to epithelial cells through promotion of the production and/or secretion of type III secreted proteins.     

Multiple elements controlling adherence of enterohemorrhagic Escherichia coli O157:H7 to HeLa cells

Adherence of enterohemorrhagic Escherichia coli (EHEC) to the intestinal epithelium is essential for initiation of infection. Intimin is the only factor demonstrated to play a role in intestinal colonization by EHEC O157:H7. Other attempts to identify additional adhesion factors in vitro have been unsuccessful, suggesting that expression of these factors is under tight regulation. We sought to identify genes involved in the control of adherence of EHEC O157:H7 to cultured epithelial cells. A total of 5,000 independent transposon insertion mutants were screened for their ability to adhere to HeLa cells, and 7 mutants were isolated with a markedly enhanced adherence. The mutants adhered at levels 113 to 170% that of the wild-type strain, and analysis of the protein profiles of these mutants revealed several proteins differentially expressed under in vitro culture conditions. We determined the sequence of the differentially expressed proteins and further investigated the function of OmpA, whose expression was increased in a mutant with an insertionally inactivated tcdA gene. An isogenic ompA mutant showed reduced adherence compared to the parent strain. Disruption of the ompA gene in the tdcA mutant strain abolished the hyperadherent phenotype, and anti-OmpA serum inhibited adhesion of wild-type and tdcA mutant strains to HeLa cells. Enhanced adhesion mediated by OmpA was also observed with Caco-2 cells, and anti-OmpA serum blocked adherence to HeLa cells of other EHEC O157:H7 strains. Our results indicate that multiple elements control adherence and OmpA acts as an adhesin in EHEC O157:H7.     

Cloning, expression, and characterization of fimbrial operon F9 from enterohemorrhagic Escherichia coli O157:H7

Recent transposon mutagenesis studies with two enterohemorrhagic Escherichia coli (EHEC) strains, a sero- type O26:H- strain and a serotype O157:H7 strain, led to identification of a putative fimbrial operon that promotes colonization of young calves (1 to 2 weeks old). The distribution of the gene encoding the major fimbrial subunit present in O-island 61 of EHEC O157:H7 in a characterized set of 78 diarrheagenic E. coli strains was determined, and this gene was found in 87.2% of the strains and is therefore not an EHEC-specific region. The cluster was amplified by long-range PCR and cloned into the inducible expression vector pBAD18. Induced expression in E. coli K-12 led to production of fimbriae, as demonstrated by transmission electron microscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The fimbriae were purified, and sera to the purified major subunit were raised and used to demonstrate expression from wild-type E. coli O157:H7 strains. Induced expression of the fimbriae, designated F9 fimbriae, was used to characterize binding to bovine epithelial cells, bovine gastrointestinal tissue explants, and extracellular matrix components. The fimbriae promoted increases in the levels of E. coli K-12 binding only to bovine epithelial cells. In contrast, induced expression of F9 fimbriae in E. coli O157:H7 significantly reduced adherence of the bacteria to bovine gastrointestinal explant tissue. This may have been due to physical hindrance of type III secretion-dependent attachment. The main F9 subunit gene was deleted in E. coli O157:H7, and the resulting mutant was compared with the wild-type strain for colonization in weaned cattle. While the shedding levels of the mutant were reduced, the animals were still colonized at the terminal rectum, indicating that the adhesin is not responsible for the rectal tropism observed but may contribute to colonization at other sites, as demonstrated previously with very young animals.     

Characterization of flagella purified from enterohemorrhagic, vero-cytotoxin-producing Escherichia coli serotype O157:H7.

Escherichia coli of the serotype O157:H7 has recently been isolated in human fecal specimens in association with sporadic cases and outbreaks of hemorrhagic colitis and with the hemolytic uremic syndrome. The aim of this study was to characterize the flagellin protein subunit constituents of flagellar filaments from E. coli O157:H7 strain CL-56. Flagellin isolated from a reference Salmonella enteritidis strain was used for comparison. Flagella were dissociated by incubation of bacteria under acidic conditions, centrifugation, and differential ammonium sulfate precipitation. Reconstituted flagellar filaments were demonstrated by three complementary methods: transmission electron microscopy, antigenic reactivity with H7 antiserum by a dot blot immunoassay, and immunogold localization of antiserum raised to the purified antigen to intact flagella on whole E. coli O157:H7. On sodium dodecyl sulfate-polyacrylamide gels flagellin proteins from E. coli O157:H7 demonstrated an apparent Mr of 66,000. The isoelectric point of E. coli O157:H7 flagellin was 5.42. By immunoblotting, H7 flagellin proteins were shown to be immunogenic. They induced a systemic immune response both in rabbits challenged with whole bacteria and in a human previously infected with E. coli O157:H7.     

Long polar fimbriae of enterohemorrhagic Escherichia coli O157:H7 bind to extracellular matrix proteins

Adherence to intestinal cells is a key process in infection caused by enterohemorrhagic Escherichia coli (EHEC). Several adhesion factors that mediate the binding of EHEC to intestinal cells have been described, but the receptors involved in their recognition are not fully characterized. Extracellular matrix (ECM) proteins might act as receptors involved in the recognition of enteric pathogens, including EHEC. In this study, we sought to characterize the binding of EHEC O157:H7 to ECM proteins commonly present in the intestine. We found that EHEC prototype strains as well as other clinical isolates adhered more abundantly to surfaces coated with fibronectin, laminin, and collagen IV. Further characterization of this phenotype, by using antiserum raised against the LpfA1 putative major fimbrial subunit and by addition of mannose, showed that a reduced binding of EHEC to ECM proteins was observed in a long polar fimbria (lpf) mutant. We also found that the two regulators, H-NS and Ler, had an effect in EHEC Lpf-mediated binding to ECM, supporting the roles of these tightly regulated fimbriae as adherence factors. Purified Lpf major subunit bound to all of the ECM proteins tested. Finally, increased bacterial adherence was observed when T84 cells, preincubated with ECM proteins, were infected with EHEC. Taken together, these findings suggest that the interaction of Lpf and ECM proteins contributes to the EHEC colonization of the gastrointestinal tract.     

Mouse model for colonization and disease caused by enterohemorrhagic Escherichia coli O157:H7.

Enterohemorrhagic Escherichia coli O157:H7 isolates produce Shiga-like toxins and carry a 60-megadalton plasmid which encodes an adhesin for Henle 407 intestinal cells. A streptomycin-treated mouse model was used to compare the intestinal colonizing capacity of E. coli O157:H7 strain 933 with that of its 60-megadalton plasmid-cured derivative, strain 933cu. When fed individually to mice, both 933 and 933cu maintained a stable number of organisms per gram of feces, and the greatest numbers of 933 or 933cu were isolated from cecal and proximal colonic epithelial cells. When 933 and 933cu were simultaneously fed to mice, 933cu was unable to maintain a stable level of colonization in about two-thirds of the mice tested. However, in one-third of the mice, the number of 933cu in feces began to increase rapidly until a stable level of co-colonization with 933 was attained. The isolate from these mice, 933cu-rev, was excreted in high numbers when fed alone to mice and was found on epithelial cells throughout the entire large bowel and distal small intestine. Moreover, 933cu-rev grew in mucus from all segments of the intestine and at higher levels than strain 933 or 933cu. Only mice fed strain 933cu-rev died. Histopathological studies confirmed that mice fed 933cu-rev died from bilateral renal cortical tubular necrosis consistent with toxic insult, perhaps due to Shiga-like toxins. The virulence of 933cu-rev may reflect its ability to grow well in mucus and colonize the small as well as large bowel.     

Cortactin recruitment by enterohemorrhagic Escherichia coli O157:H7 during infection in vitro and ex vivo

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is an important human pathogen that colonizes the gut mucosa via attaching and effacing (A/E) lesions; A/E lesion formation in vivo and ex vivo is dependent on the type III secretion system (T3SS) effector Tir. Infection of cultured cells by EHEC leads to induction of localized actin polymerization, which is dependent on Tir and a second T3SS effector protein, TccP, also known as EspF_U. Recently, cortactin was shown to bind both the N terminus of Tir and TccP via its SH3 domain and to play a role in EHEC-triggered actin polymerization in vitro. In this study, we investigated the recruitment of cortactin to the site of EHEC adhesion during infection of in vitro-cultured cells and mucosal surfaces ex vivo (using human terminal ileal in vitro organ cultures [IVOC]). We have shown that cortactin is recruited to the site of EHEC adhesion in vitro downstream of TccP and N-WASP. Deletion of the entire N terminus of Tir or replacing the N-terminal polyproline region with alanines did not abrogate actin polymerization or cortactin recruitment. In contrast, recruitment of cortactin to the site of EHEC adhesion in IVOC is TccP independent. These results imply that cortactin is recruited to the site of EHEC adhesion in vitro and ex vivo by different mechanisms and suggest that cortactin might have a role during EHEC infection of mucosal surfaces.     

Identification and characterization of lpfABCC'DE,a fimbrial operon of enterohemorrhagic Escherichia coli O157:H7

The mechanisms underlying the adherence of Escherichia coli O157:H7 and other enterohemorrhagic E. coli (EHEC) strains to intestinal epithelial cells are poorly understood. We have identified a chromosomal region (designated lpfABCC'DE) in EHEC O157:H7 containing six putative open reading frames that was found to be closely related to the long polar (LP) fimbria operon (lpf) of Salmonella enterica serovar Typhimurium, both in gene order and in conservation of the deduced amino acid sequences. We show that lpfABCC'DE is organized as an operon and that its expression is induced during the exponential growth phase. The lpf genes from EHEC strain EDL933 were introduced into a nonfimbriated (Fim(-)) E. coli K-12 strain, and the transformed strain produced fimbriae as visualized by electron microscopy and adhered to tissue culture cells. Anti-LpfA antiserum recognized a ca. 16-kDa LpfA protein when expressed under regulation of the T7 promoter system. The antiserum also cross-reacted with the LP fimbriae in immunogold electron microscopy and Western blot experiments. Isogenic E. coli O157:H7 lpf mutants derived from strains 86-24 and AGT300 showed slight reductions in adherence to tissue culture cells and formed fewer microcolonies compared with their wild-type parent strains. The adherence and microcolony formation phenotypes were restored when the lpf operon was introduced on a plasmid. We propose that LP fimbriae participate in the interaction of E. coli O157:H7 with eukaryotic cells by assisting in microcolony formation.     

Particular biochemical profiles for enterohemorrhagic Escherichia coli O157:H7 isolates on the ID 32E system

The ability of the ID 32E system to identify and discriminate 74 Escherichia coli O157 isolates among 106 E. coli non-O157 isolates was evaluated. The results showed atypical biochemical reactions but accurate identification at the species level and no unique biochemical profile numbers for E. coli O157, although these numbers were distinct from those of other serotypes.     

Phenotypic and molecular analysis of tellurite resistance among enterohemorrhagic Escherichia coli O157:H7 and sorbitol-fermenting O157:NM clinical isolates

A total of 66 (98.5%) of 67 enterohemorrhagic Escherichia coli (EHEC) O157:H7 strains had increased potassium tellurite (Te) MICs (32 to 1,024 microg/ml), grew on Te-containing media, and possessed Te resistance (ter) genes, whereas 83 (96.5%) of 86 sorbitol-fermenting (SF) EHEC O157:NM strains had Te MICs of 相似文献   

肠出血性大肠埃希菌O157:H7 TCCP蛋白与宿主细胞IRTKS蛋白的相互作用

目的通过体外结合实验验证EHEC O157:H7内膜素受体偶联细胞骨架蛋白重复片段与人肠上皮细胞IRTKS蛋白SH3结构域之间的相互作用,并制备二者蛋白复合体,为利用晶体学方法研究其相互作用奠定基础。方法将IRTKS蛋白的SH3结构域cDNA序列克隆至pET30a表达质粒,转化BL21(DE3),诱导表达纯化SH3(IRTKS)蛋白;制备TCCP重复片段TC-CP(3R)蛋白;将SH3(IRTKS)与TCCP(3R)按照不同比例混合后,非变性丙烯酰胺凝胶电泳鉴定两者相互结合后产物;利用分子筛层析收集标准蛋白、TCCP(3R)、SH3(IRTKS)和TCCP(3R)-SH3(IRTKS)复合体的出峰体积,回归计算复合物的分子量,分析蛋白相互结合的比例。结果成功克隆表达了SH3(IRTKS)重组质粒;并制备了高纯度的SH3(IRTKS)和TCCP(3R)蛋白;非变性丙烯酰胺凝胶电泳结果证实TCCP(3R)与SH3(IRTKS)发生相互作用形成了蛋白质复合体;复合体的分子量约为33 000,二者相互结合的比例约为1:1。结论本研究为TCCP重复片段与SH3(IRTKS)相互作用提供了直接证据,同时复合体的制备,为利用晶体学研究两者的相互作用奠定了基础。     

Screening for Escherichia coli O157:H7 in Illinois

Objective: To determine the incidence of infection with Escherichia coli O157:H7 in a tertiary referral center in Chicago, where a similar study had been performed in 1984, to evaluate cases of disease reported to the Illinois Department of Public Health (IDPH) in 1993, and to determine laboratory practices used to detect this infection throughout the state.
Methods: During a 6-month period in 1993, all stool specimens at Rush-Presbyterian-St Luke's Medical Center (RPSLMC) were tested for E. coli O157:H7. Reports of diagnosed E. coli O157:H7 cases investigated by IDPH were also reviewed. A survey of 73 hospitals in the Chicago area was performed to determine routine culturing practices, specifically, the selection of stool specimens for evaluation for this pathogen.
Results: In the RPSLMC survey, two cases were identified among 1985 samples (incidence 0.1%), similar to the 0.08% incidence detected in a similar study conducted at the same institution in 1984. Through passive surveillance, the IDPH received 44 reports of E. coli O157:H7 in 1993. The hospital survey revealed that, in the seven labs testing all stool specimens for E. coli O157:H7, an incidence of 16/8137 specimens (0.2%) was determined.
Conclusions: These data suggest that sporadic E. coli O157:H7 remains uncommon in Illinois and that the incidence may not have changed over a 9-year period. The low yield and substantial cost of culturing all stools suggest that only specimens from patients with bloody diarrhea should be evaluated routinely in areas of low endemicity.     

Viable but non-culturable state and toxin gene expression of enterohemorrhagic Escherichia coli O157 under cryopreservation

As major food-borne pathogens worldwide, Escherichia coli are capable of toxin production directly causing severe human disease. However, routine methods are incapable of detecting viable but non-culturable (VBNC) bacteria in food products and raw materials, leading to false-negative identification. In this study, VBNC E. coli O157 strains were acquired after cryopreservation at −20 °C, with and without freeze-thawing; morphology was observed to be of shorter rod-shape, and toxin expression remained at relatively high levels. PMA-PCR assay for VBNC detection was also validated. Therefore, these results suggest that VBNC E. coli O157 strains may represent a strong threat to public health and food safety.     

Lactobacillus rhamnosus strain GG prevents enterohemorrhagic Escherichia coli O157:H7-induced changes in epithelial barrier function

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 intimately attaches to intestinal epithelial monolayers and produces attaching and effacing (A/E) lesions. In addition, EHEC infection causes disruptions of intercellular tight junctions, leading to clinical sequelae that include acute diarrhea, hemorrhagic colitis, and the hemolytic-uremic syndrome. Current therapy remains supportive since antibiotic therapy increases the risk of systemic complications. This study focused on the potential therapeutic effect of an alternative form of therapy, probiotic Lactobacillus rhamnosus strain GG, to attenuate EHEC-induced changes in paracellular permeability in polarized MDCK-I and T84 epithelial cell monolayers. Changes in epithelial cell morphology, electrical resistance, dextran permeability, and distribution and expression of claudin-1 and ZO-1 were assessed using phase-contrast, immunofluorescence, and transmission electron microscopy and macromolecular flux. This study demonstrated that pretreatment of polarized MDCK-I and T84 cells with the probiotic L. rhamnosus GG reduced morphological changes and diminished the number of A/E lesions induced in response to EHEC O157:H7 infection. With probiotic pretreatment there was corresponding attenuation of the EHEC-induced drop in electrical resistance and the increase in barrier permeability assays. In addition, L. rhamnosus GG protected epithelial monolayers against EHEC-induced redistribution of the claudin-1 and ZO-1 tight junction proteins. In contrast to the effects seen with the live probiotic, heat-inactivated L. rhamnosus GG had no effect on EHEC binding and A/E lesion formation or on disruption of the barrier function. Collectively, these findings provide in vitro evidence that treatment with the probiotic L. rhamnosus strain GG could prove to be an effective management treatment for preventing injury of the epithelial cell barrier induced by A/E bacterial enteropathogens.     

Contribution of the twin arginine translocation system to the virulence of enterohemorrhagic Escherichia coli O157:H7

Shiga toxin-producing Escherichia coli O157:H7 is a major food-borne infectious pathogen. In order to analyze the contribution of the twin arginine translocation (TAT) system to the virulence of E. coli O157:H7, we deleted the tatABC genes of the O157:H7 EDL933 reference strain. The mutant displayed attenuated toxicity on Vero cells and completely lost motility on soft agar plates. Further analyses revealed that the ΔtatABC mutation impaired the secretion of the Shiga toxin 1 (Stx1) and abolished the synthesis of H7 flagellin, which are two major known virulence factors of enterohemorrhagic E. coli O157:H7. Expression of the EDL933 stxAB₁ genes in E. coli K-12 conferred verotoxicity on this nonpathogenic strain. Remarkably, cytotoxicity assay and immunoblot analysis showed, for the first time, an accumulation of the holotoxin complex in the periplasm of the wild-type strain and that a much smaller amount of StxA₁ and reduced verotoxicity were detected in the ΔtatC mutant cells. Together, these results establish that the TAT system of E. coli O157:H7 is an important virulence determinant of this enterohemorrhagic pathogen.     

Characterization of Escherichia coli serotype O157:H7.

A total of 174 strains of Escherichia coli serotype O157:H7 representing human isolates obtained from outbreaks and sporadic cases of hemorrhagic colitis, hemolytic-uremic syndrome, and nonbloody diarrheal illnesses as well as from asymptomatic carriers across Canada and the United States were examined. E. coli serotype O157:H7 possessed distinct biochemical markers, a 100% negative reaction for beta-glucuronidase and sorbitol, and a 100% positive reaction for raffinose and dulcitol; all strains otherwise were biochemically typical of E. coli. The vast majority (97%) of the strains were susceptible to commonly used antimicrobial agents. All strains produced readily detectable levels of Verotoxin; however, with polymyxin extraction, nearly 50% of the strains showed up to a 10-fold increase in the toxin level. None were found to mediate hemagglutination of human group A erythrocytes with or without D-mannose. The majority (approximately 70%) of the strains showed localized and diffuse adherence to HEp-2 cells and Henle 407 cells, and the adherence patterns were not very different from those observed among other E. coli strains. Twenty phage types were recognized, with phage types 1 and 2 accounting for 65% of the test strains. Plasmid analysis indicated three basic plasmid profiles: profile I was characterized by 68.7- and 4.2-megadalton (MDa) plasmids (62% of strains), profile II was characterized by 66.2- and 1.8-MDa plasmids (20% of strains), and profile III was characterized by a 62.5-MDa plasmid (18% of strains). A small number (19%) of the strains carried at least one additional plasmid over the basic complements, and these could be considered to constitute a miscellaneous category. None of the above-described characteristics of E. coli serotype O157:H7 could be directly correlated with one another, with the nature of infection, or with the geographical distribution of strains.     

The StcE protease contributes to intimate adherence of enterohemorrhagic Escherichia coli O157:H7 to host cells

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a diarrheal pathogen that causes attaching and effacing (A/E) lesions on intestinal epithelial cells. Strains of the O157 serogroup carry the large virulence plasmid pO157, which encodes the etp type II secretion system that secretes the genetically linked zinc metalloprotease StcE. The Ler regulator controls expression of many genes involved in A/E lesion formation, as well as StcE, suggesting StcE may be important at a similar time during colonization. Our laboratory has previously demonstrated that StcE cleaves C1-esterase inhibitor, a regulator of multiple inflammation pathways. Here we report two new substrates for StcE, mucin 7 and glycoprotein 340, and that purified StcE reduces the viscosity of human saliva. We tested the hypothesis that StcE contributes to intimate adherence of EHEC to host cells by cleavage of glycoproteins from the cell surface. The fluorescent actin stain (FAS) test was used to observe the intimate adherence represented by fluorescently stained bacteria colocalized with regions of bundled actin formed on HEp-2 cells. An E. coli O157:H7 strain with a stcE gene deletion was not affected in its ability to generally adhere to HEp-2 cells, but it did score threefold lower on the FAS test than wild-type or complemented strains. Addition of exogenous recombinant StcE increased intimate adherence of the mutant to wild-type levels. Thus, StcE may help block host clearance of E. coli O157:H7 by destruction of some classes of glycoproteins, and it contributes to intimate adherence of E. coli O157:H7 to the HEp-2 cell surface.