Distinctive patterns of adherence of enteropathogenic Escherichia coli to HeLa cells

Construction of an eae deletion mutant of enteropathogenic Escherichia coli by using a positive-selection suicide vector

The ability to attach to epithelial cells, efface the microvillus surface, and disrupt the underlying cytoskeleton is characteristic of enteropathogenic Escherichia coli (EPEC). Recently, eae, a gene necessary for this phenomenon, was described (A. E. Jerse, J. Yu, B. D. Tall, and J. B. Kaper, Proc. Natl. Acad. Sci. USA 87:7839-7843, 1990). We report the use of a novel suicide vector containing the pir-dependent R6K replicon and the sacB gene of Bacillus subtilis to construct an eae deletion mutant of EPEC. This system enables positive selection for the loss of vector sequences. The resulting mutant, CVD206, is indistinguishable from the wild-type strain except for the loss of a 94-kDa outer membrane protein and attaching and effacing ability. Both the 94-kDa outer membrane protein and attaching and effacing ability are restored upon reintroduction of the eae gene on a plasmid. These results confirm the role of the eae gene in the attaching and effacing activity of EPEC and establish the utility of a new system for the construction of deletion mutations.

Use of purified F1845 fimbrial adhesin to study localization and expression of receptors for diffusely adhering Escherichia coli during enterocytic differentiation of human colon carcinoma cell lines HT-29 and Caco-2 in culture

Whole diffusely adhering Escherichia coli (DAEC) C1845 cells bearing the F1845 adhesive factor bind diffusely to differentiated human colon carcinoma cell lines HT-29 and Caco-2. By using antibodies directed against the purified fimbrial adhesin F1845 factor, the expression of the DAEC F1845-specific brush border receptors in the polarized human intestinal HT-29 and Caco-2 epithelial cells was studied by indirect immunofluorescence. A low level of DAEC F1845 receptors in undifferentiated intestinal cells was detected; they were localized in a cluster of cells. DAEC F1845 receptors were expressed at a high level in differentiated HT-29 and Caco-2 cells. DAEC F1845 receptors were expressed at a strikingly high level in the apical domains of the cells and developed during enterocytic differentiation in culture, in parallel with the apical expression of the intestinal brush border hydrolase, sucrase-isomaltase.

Localized adherence by enteropathogenic Escherichia coli is an inducible phenotype associated with the expression of new outer membrane proteins

Enteropathogenic Escherichia coli grow as discrete colonies on the mucous membranes of the small intestine. A similar pattern can be demonstrated in vitro; termed localized adherence (LA), it is characterized by the presence of circumscribed clusters of bacteria attached to the surfaces of cultured epithelial cells. The LA phenotype was studied using B171, an O111:NM enteropathogenic E. coli (EPEC) strain, and HEp-2 cell monolayers. LA could be detected 30-60 min after exposure of HEp-2 cells to B171. However, bacteria transferred from infected HEp-2 cells to fresh monolayers exhibited LA within 15 min, indicating that LA is an inducible phenotype. Induction of the LA phenotype was found to be associated with de novo protein synthesis and changes in the outer membrane proteins, including the production of a new 18.5-kD polypeptide. A partial NH2-terminal amino acid sequence of this polypeptide was obtained and showed it to be identical through residue 12 to the recently described bundle-forming pilus subunit of EPEC. Expression of the 18.5-kD polypeptide required the 57-megadalton enteropathogenic E. coli adherence plasmid previously shown to be required for the LA phenotype in vitro and full virulence in vivo. This observation, the correspondence of the 18.5-kD polypeptide to an EPEC-specific pilus protein, and the temporal correlation of its expression with the development of the LA phenotype suggest that it may contribute to the EPEC colonial mode of growth.

HeLa cell adherence, actin aggregation, and invasion by nonenteropathogenic Escherichia coli possessing the eae gene

Enteropathogenic Escherichia coli (EPEC) produce diarrhea in humans by a mechanism that involves close adherence to epithelial cells in the intestine and colon. Close adherence is associated with effacement of microvilli and condensation of actin beneath the bacteria, a process termed attaching/effacing adherence. Attaching/effacing adherence of EPEC occurs in vitro in tissue culture, simplifying the study of the molecular genetics of this process. An EPEC gene (eae) necessary for attaching/effacing adherence was recently characterized. Enterohemorrhagic E. coli and the rabbit-specific RDEC-1 strain adhere in a like fashion in vivo and hybridize with eae. However, these strains adhere poorly to tissue culture cells, complicating the in vitro study of attaching/effacing adherence. In order to develop an in vitro model for the study of attaching/effacing activity of non-EPEC bacteria, a plasmid encoding the F1845 adhesin of an E. coli strain (C1845) isolated from a patient with diarrhea was transformed into RDEC-1 and enterohemorrhagic E. coli. The transformed strains adhered in a diffuse pattern to HeLa cells, and they aggregated HeLa cell actin at points of adherence in the fluorescein-isothiocyanate-labeled phalloidin assay. They also invaded HeLa cells in a gentamicin invasion assay, although not to the extent seen with EPEC. The construction of adherent non-EPEC strains facilitates the molecular study of the attaching/effacing properties and invasiveness of these strains in tissue culture models.

Studies on adherence and outer membrane protein of enteropathogenic Escherichia coli 0127: H6 and their related plasmids

The following characteristics were found in 20 epidemic strains of enteropathogenic Escherichia coli (EPEC) 0127: H6 isolated from an outbreak of neonatal diarrhea: 1) Absent Vero toxin production; 2) No potential for invasiveness; 3) Possession of 1.5 and 60 Md plasmid identical restriction digest and outer membrane protein (OMP) patterns; 4) Ability of localized adherence to HEp-2, HeLa and FL cells; 5) Capability to cause diarrhea in rabbits with destruction of the ileal microvilli at the areas of bacterial adherence. After elimination of the 60 Md plasmid from EPEC 0127: H6 the 45 and 82 Kd OMPs of the parent strain were lost. These plasmid-cured strains became non-adherent to HEp-2, HeLa and FL cells, and unable to cause diarrhea in rabbits. These results suggest that the pathogenic mechanism of EPEC 0127: H6 induced diarrhea may be related to the genes on a 60 Md plasmid expressed as 45 and 82 Kd OMPs which cause localized adherence to epithelial cells and destruction of ileal microvilli. This damage leads to a marked reduction in absorptive surface area, resulting in diarrhea.

Plasmid and chromosomal elements involved in the pathogenesis of attaching and effacing Escherichia coli

Attaching and effacing (A/E) intestinal lesions are produced by enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC), and RDEC-1, a pathogen of weanling rabbits. We recently identified a chromosomal locus (eae[E. coli A/E]) which is required for A/E activity in a wild-type EPEC strain. Sequences homologous to those of an eae gene probe were detected in EPEC, RDEC-1, and EHEC isolates. We report here that the eae gene is chromosomally encoded in all EPEC and EHEC strains tested and in RDEC-1. In addition, the eae probe was found to be 100% sensitive and 98% specific in detecting E. coli of EPEC serogroups that demonstrate A/E activity. Ten percent of E. coli of EPEC serogroups that hybridized with the eae probe and produced A/E activity did not hybridize with the EAF (EPEC adherence factor) probe, a plasmid-associated diagnostic probe which is currently used to identify EPEC. In addition to A/E factors, plasmid-associated adhesins also contribute to the pathogenesis of EPEC and RDEC-1. To further investigate the role of plasmid-associated adherence, a hybrid RDEC-1-EPEC strain containing the adherence plasmid of an EPEC strain in the A/E background of RDEC-1 was constructed. This hybrid strain, unlike the parent RDEC-1 strain, produced A/E lesions on human tissue culture cells, which suggests that the EPEC adherence plasmid provides tissue specificity to the hybrid strain and that the A/E factors of RDEC-1 are not host restricted.

An inducible bundle-forming pilus of enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC), a cause of childhood diarrhea, grow on the surface of the small intestine and on cultured epithelial cells as colonies of adherent bacteria. When propagated on solid medium containing blood or attached to HEp-2 cells, EPEC express ropelike bundles of filaments, termed bundle-forming pili (BFP), that create a network of fibers that bind together the individual organisms. BFP were found to be expressed by five EPEC serogroups, each harboring a approximately 92-kilobase plasmid previously known to be important for virulence in humans. When two of these strains were cured of this plasmid, they neither expressed BFP nor grew as adherent colonies. An antiserum to BFP reduced the capacity of EPEC to infect cultured epithelial cells. BFP are composed of a repeating subunit of 19,500 daltons, the amino-terminal amino acid sequence of this subunit is homologous to that of the toxin-coregulated pilin of Vibrio cholerae.

Relative importance of eight virulence characteristics of pyelonephritogenic Escherichia coli strains assessed by multivariate statistical analysis

We have previously reported univariate statistical analysis of the prevalences of putative virulence determinants in Escherichia coli isolated from children and adults with acute pyelonephritis. The expression of P-fimbriae, cell surface hydrophobicity, mannose resistant haemagglutination, haemolysin synthesis, cytotoxic necrotizing factor production and aerobactin mediated iron uptake occurred more often in a collection of 115 Escherichia coli strains isolated from children and women with acute non-obstructive pyelonephritis compared to 96 strains isolated from the commensal fecal flora. With the aim to study which of these virulence markers were independently associated with strains causing infection we performed a multivariate statistical analysis with the data from these strains. The previously proposed virulence factors, expression of type 1 fimbriae and adhesion to HeLa cells were also included in the analysis. P-fimbriae, mannose resistant haemagglutination and the production of haemolysin were, in the multivariate analysis, associated with strains isolated from patients with acute pyelonephritis.

Identification of carbohydrate structures as receptors for localised adherent enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli strains of diffused adherent (DA) and localised adherent (LA) phenotypes were tested for their ability to bind to glycolipids. DA strains did not bind to the glycolipids tested, while LA strains bound to asialo GM1, asialo GM2, globoside and lacto-N-neotetraose in decreasing order of avidity. The minimum common sequence among the four glycolipids could be delineated as GalNac beta 1-4 Gal as the binding epitope with GalNac beta 1-3 Gal and GlcNac beta 1-3 Gal serving as relatively weaker binders. The binding was not inhibited by a variety of free oligosaccharides or by the neoglycoproteins tested. Adhesion-negative mutants of an enteropathogenic LA strain showed a markedly reduced binding to asialo GM1 indicating that the recognition of GalNac beta 1-4 Gal was correlated with the ability to adhere to HeLa cells. Thus recognition and binding to glycolipids could play an important role in colonisation through adherence to intestinal surfaces.

Characteristics of adherence of enteroaggregative Escherichia coli to human and animal mucosa

An Escherichia coli strain (serotype O127a:H2) that had been isolated from a child with diarrhea in Thailand and that was negative for the virulence factors of the four categories of diarrheagenic E. coli (enterotoxigenic, enteropathogenic, enteroinvasive, and enterohemorrhagic) and that showed an aggregative pattern of adherence to HeLa cells was investigated for adherence to native or Formalin-fixed human and animal mucosa. The hemagglutinating activity and adherence ability of the bacteria were resistant to D-mannose and were strictly regulated by environmental conditions. Genetic data supported the close relation between the hemagglutinating activity and adherence ability. In accordance with the adherence pattern on tissue-cultured cells, the bacteria adhered to human and animal mucosa, as evidenced by a direct gold-labeling analysis. In human intestines, Formalin-fixed mucous coatings, epithelial cells of colonic mucosa, epithelial cells of ileal single lymphoid follicles and Peyer's patches, and the absorptive cells of jejunal or ileal villi provided adherence targets. Adherence to M cells in the Peyer's patch-associated epithelium was also confirmed. The adherence levels to native jejunal or ileal human villi were low, as was the case with the corresponding Formalin-fixed villi. In human urinary tract, the superficial epithelial cells of both native and Formalin-fixed ureter provided striking adherence targets. In animal (porcine and rabbit) small intestines, the bacteria adhered to the native villi to a lesser extent than to the Formalin-fixed villi. The adherence levels were compared with those of enterotoxigenic E. coli with colonization factor antigen (CFA)/I pili or CFA/II pili. The data suggested unique mucosa adherence characteristics of the enteroaggregative E. coli strain. The possibility of the adherence ability as a virulence factor was discussed.

Diarrhoeal disease in children less than one year of age at a children's hospital in Guangzhou, People's Republic of China

We performed a case-control study of diarrhoea to determine its causes in children less than 1 year old in Guangzhou, People's Republic of China, in April to September 1989. Stools were cultured for Salmonella, Shigella, Campylobacter and vibrios by standard techniques; rotavirus (RV) was identified by polyacrylamide gel electrophoresis; and specific deoxyribonucleic acid probes were used to identify Escherichia coli containing genes coding for Shiga-like toxin I and II, enteropathogenic E. coli adherence factor, and enteroinvasive E. coli (EIEC). E. coli isolates were tested for heat-labile toxin (LT) and heat-stable toxin (ST) production and mannose-resistant adherence to HeLa cells. Rotavirus was identified in 13 of 174 children with diarrhoea (cases) and in 2% of 174 age-matched children without diarrhoea (controls), P less than 0.001. C. jejuni was identified in 10% of cases and 2% of controls, P = 0.003. Giardia lamblia was identified in 4 cases, LT and ST enterotoxigenic E. coli (ETEC) in 2, and S. flexneri in 1 case; they were not found in controls. ETEC that produced LT only was isolated from 5 cases and 3 controls, P = 0.721; E. coli that adhered to HeLa cells in a diffuse pattern was isolated from 30 cases and 40 controls, P = 0.229; and E. coli that adhered in an aggregative pattern was isolated from 20 cases and 18 controls, P = 0.863. EIEC was not isolated from cases or controls. Nine cases (5%) developed persistent diarrhoea (greater than 14 d duration). C. jejuni and aggregative E. coli were isolated from different children with persistent diarrhoea.(ABSTRACT TRUNCATED AT 250 WORDS)

Mannose-resistant adhesion of motile Aeromonas to INT407 cells and the differences among isolates from humans, food and water

Aeromonas has been recognized as an important enteropathogen, but factors related to its virulence have not been clarified. For most enteric pathogens, attachment is a prerequisite for infection and for the effective delivery of toxins to the intestinal epithelial cells. We examined a total of 273 strains isolated from stool, food and environmental specimens by an assay for mannose-resistant adhesion to INT407 cells in vitro. Seventeen of the 102 faecal isolates were adhesive strains with more than 10 bacteria adhering per cell, while only 2 of the 118 isolates from foods and river water adhered to the cells (P less than 0.001). It is possible that the adhesion might serve as a marker for discrimination between the pathogenic and nonpathogenic isolates. The 8 highly adhesive strains with more than 20 adhering organisms per cell were scrutinized for the mechanism of adhesion. No correlation was apparent between the adhesion to INT407 cells and hydrophobicity. It was noted that fucose inhibited the adhesion of four strains as well as haemagglutination by them. Electronmicroscopic studies showed the presence of flexible and curvilinear fimbriae in only 2 of the 8 highly adhesive strains.

Serotype O157:H7 Escherichia coli from bovine and meat sources

Serotype O157:H7 Escherichia coli strains from several different bovine and meat (beef) sources were studied to determine the diversity of their virulence properties and to compare their plasmid characteristics. Eighteen strains from cattle feces, 2 from water buffalo feces, 3 from beef samples, and 2 from feces of human hemolytic uremic syndrome cases were examined. All of these strains hybridized with the CVD419 DNA probe which identifies serotype O157:H7 and many other serotypes of verocytotoxin-producing E. coli. Of 15 bovine strains that hybridized with two verocytotoxin DNA probes, 8 hybridized with both verocytotoxin 1 (VT1) and VT2 probes, 5 hybridized with only the VT2 probe, and 2 hybridized with only the VT1 probe. This distribution was similar to that reported for O157:H7 E. coli isolated from humans. All three beef isolates hybridized with both VT1 and VT2 probes. All strains that hybridized with the VT probes were positive in the verocytotoxin assay, and all probe-negative strains were negative in the assay. All the strains possessed large plasmids with molecular sizes ranging from 53 to 64 MDa. Fifteen of the 20 cattle and water buffalo strains had one or more additional small plasmids. Restriction patterns resulting from HindIII, SmaI, and BamHI digestions of the large plasmids were used to compare all possible pairs of five different single plasmid-bearing strains from different countries (Egypt, England, and the United States). The restriction patterns of these strains were distinct, and the mean coefficients of similarity for these comparisons ranged from 71 to 91%, indicating a moderate degree of genetic diversity. This diversity and the presence of multiple plasmids in many bovine and human O157:H7 strains reinforce the usefulness of plasmid analysis in future studies. Only four of the 20 bovine strains and 1 of the 3 beef strains possessed the capability for adherence to HEp-2 and Intestine 407 cells in the presence of mannose, indicating that in vitro expression of localized adherence is not a universal property of O157:H7 strains of bovine origin.

Elevation of intracellular free calcium levels in HEp-2 cells infected with enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) are a class of diarrheagenic organisms that induce a characteristic attaching and effacing lesion in enterocytes and various cultured cell lines. Infection of cultured HEp-2 cells by EPEC isolates 2036-80 (serotype O119) and E2348-69 (serotype O127) resulted in significant elevation of intracellular free calcium levels, determined quantitatively with the fluorescent calcium indicator dye 2-([2-bis(carboxymethyl)amino-5-methylphenoxy]methyl)-6-methoxy-8- bis(carboxymethyl)aminoquinoline. This effect, which was not observed on infection with non-lesion-forming E. coli strains, was inhibited by dantrolene, a drug that prevents calcium mobilization from intracellular stores. Moreover, activated protein kinase C in infected cells was dissociated from cell membranes by a process that was inhibited by cyclosporin A, suggesting involvement of the calcium-dependent protease calpain. A qualitative method for observing intracellular calcium fluxes by fluorescence microscopy with the recently described fluorescein-based indicator fluo-3 was used to screen a collection of well-characterized E. coli isolates from patients with infantile enteritis. Increased localized calcium-dependent fluo-3 fluorescence was observed only in HEp-2 cells infected with known lesion-forming EPEC strains. We propose that enhancement of intracellular free calcium levels in enterocytes infected with EPEC would result in formation of the characteristic lesion by calcium-dependent activation of actin-depolymerizing proteins, with eventual loss of absorptive capacity.

Localized adherence and attaching-effacing properties of nonenteropathogenic serotypes of Escherichia coli

Traditional enteropathogenic Escherichia coli serotypes demonstrate a plasmid-mediated localized adherence in cultured HeLa or HEp-2 cells and induce an attaching-effacing intestinal lesion, both of which are considered pathognomonic and causes of diarrhea. This study describes three E. coli strains from infantile diarrhea which share these properties but belong to serotypes (O2:H2, O2:H25 and O15:H2) not considered enteropathogenic.

Molecular structure of the Dr adhesin: nucleotide sequence and mapping of receptor-binding domain by use of fusion constructs

The Dr hemagglutinin of uropathogenic Escherichia coli mediates adherence to the upper urinary tract. E. coli strains which express this adhesin bind to the Dr blood group antigen and mediate mannose-resistant hemagglutination (MRHA). Chloramphenicol inhibits MRHA produced by the Dr hemagglutinin and may act as an analog for the tissue receptor at the adhesin-binding site. The nucleotide sequence of the Dr hemagglutinin fimbrial subunit was determined and found to have significant homology with that of F1845, a fimbrial adhesin associated with diarrhea, and with the afimbrial adhesin AFA-I of uropathogenic E. coli. Chimeric adhesin determinants consisting of the Dr structural subunit and F1845 accessory genes or of the F1845 structural subunit and Dr accessory genes were constructed. The Dr and F1845 determinants were shown to have a close structural relationship, with functional differences concentrated in the fimbrial subunit. Oligonucleotide-directed site-specific mutagenesis was used to facilitate construction of a hybrid adhesin subunit gene containing the amino terminus of F1845 fused to the carboxy terminus of the Dr structural gene. The resulting construct confers chloramphenicol-resistant hemagglutination when introduced into an E. coli strain expressing the cloned Dr hemagglutinin. The chloramphenicol sensitivity or resistant phenotype of MRHA produced by this family of adhesins is determined solely by the fimbrial subunit gene. Domains responsible for the chloramphenicol sensitivity of Dr-mediated MRHA reside within the amino-terminal portion of the fimbrial subunit.

Phenotypic differences and characteristics of pyelonephritogenic strains of Escherichia coli isolated from children and adults

We examined the frequency of bacterial strains expressing cell surface hydrophobicity, P-fimbriae, mannose-resistant haemagglutination (MRHA), type I fimbriae, production of aerobactin, haemolysin synthesis (Hly), production of cytotoxic necrotising factor (CNF) and HeLa cell adherence in 126 strains of Escherichia coli isolated from children (n = 65) and women (n = 61) with acute non-obstructive pyelonephritis. Previous investigations have shown that pyelonephritogenic strains of E. coli more often express hydrophobic properties, P-fimbriae, MRHA, aerobactin-mediated iron uptake, Hly and CNF production than strains isolated from the faecal flora of healthy persons. The objective of the present study was to examine phenotypic differences between strains of E. coli obtained from children with their first episode of acute pyelonephritis and strains from women with non-obstructive acute pyelonephritis. Of the pyelonephritogenic strains of E. coli isolated from children, 98% expressed cell surface hydrophobic properties compared to 82% isolated from adults (P = 0.004). Strains from children and adults had the same ability to assimilate iron and equally often expressed P-fimbriae, MRHA and type I fimbriae. Strains from children with acute pyelonephritis more significantly expressed Hly (72%) and CNF (58%) than did pyelonephritogenic strains from adults (49 and 37% respectively, P = 0.013 and P = 0.028 respectively). The frequency of HeLa cell adherence was similar and low in both groups. The phenotype aerobactin+ Hly+ and Hly+CNF+ was found significantly more often in pyelonephritogenic strains from children than in strains from adults (P = 0.006 and P = 0.028 respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Cell surface hydrophobicity, adherence to HeLa cell cultures and haemagglutination pattern of pyelonephritogenic Escherichia coli strains

Cell surface hydrophobicity, haemagglutination pattern and adherence to HeLa cells were examined in 230 strains of Escherichia coli collected from women (n = 61 strains) and children (n = 65 strains) with non-obstructive acute pyelonephritis and in 104 faecal control strains of E. coli from healthy adults (n = 71 strains) and children (n = 33 strains). Pyelonephritogenic E. coli strains showed a significantly increased incidence of hydrophobic properties (90%) and mannose resistant haemagglutination (MRHA) of human erythrocytes (83%) than faecal control strains (64 and 23% respectively, P less than 0.001 in both cases). Mannose sensitive haemagglutination (MSHA) was observed in 48% of the pyelonephritogenic E. coli strains and in 50% of the faecal control strains (NS). The incidence of adherence to HeLa cells was low both in pyelonephritogenic and faecal control strains, 6 and 7% respectively (NS). The bacterial phenotypes MRHA + MSHA + and MRHA + MSHA- appeared significantly more often in pyelonephritogenic E. coli strains (35 and 48% respectively) than in faecal control strains (5 and 17% respectively, P less than 0.001 in both cases). The phenotype MRHA- MSHA + occurred significantly more often in control strains (45%) than in pyelonephritogenic strains (13%, P less than 0.001). Eighty-three per cent of the pyelonephritogenic E. coli strains expressing hydrophobic properties showed MRHA and 50% of the hydrophobic strains showed MSHA. There were no significant correlations between cell surface hydrophobic properties and haemagglutination pattern or adherence to HeLa cells in pyelonephritogenic E. coli strains nor in faecal control strains.

HeLa cell invasion by a strain of enteropathogenic Escherichia coli that lacks the O-antigenic polysaccharide

The interaction with HeLa cells of an enteropathogenic Escherichia coli (EPEC) strain and its plasmid-cured derivative strain was examined. An O111:NM EPEC strain B171 harbours a 54 megadalton plasmid (pYR111) necessary for the expression of both localized adherence (LA) to HeLa cells and the O-repeating side chain of the lipopolysaccharide. Under light microscopy, the plasmid-cured derivative strain B171-4 was observed to interact with HeLa cells in a pattern distinct from LA. Transmission electron microscopy showed that the bacteria were internalized by HeLa cells. In contrast, strain B171 induced pedestal-like projections and invaginations of the plasma membrane, but was never completely internalized. A quantitative assay to determine the number of internalized bacteria revealed that strain B171-4 was internalized at levels 30-70-fold higher than those of avirulent E. coli strains. Cytochalasin B reduced the levels of internalization of both strain B171-4 and an enteroinvasive E. coli strain (E11), but did not affect LA by strain B171. These results suggest that EPEC strain B171 may carry a specific chromosomally determined surface factor needed to initiate internalization by HeLa cells. However, a plasmid-determined factor alters the nature of this interaction; the combined effects of the chromosomal and plasmid determinants lead to the characteristic attachment of the bacteria in clusters on the surface of the eukaryotic cell.

Adhesion of Escherichia coli strains isolated from diarrheic weaned rabbits to intestinal villi and HeLa cells

Thirty-eight strains, representative of 575 Escherichia coli isolates from weaned diarrheic rabbits, were tested for their ability to adhere in vitro to rabbit intestinal villi and to HeLa 229 cells. The O103 rhamnose-negative, highly pathogenic strains, which are epidemiologically predominant in France, attached to intestinal villi prepared from 8-day-old as well as 6-week-old rabbits and gave a diffuse adhesion pattern with HeLa cells. These adhesion properties were associated with the presence of a protein with a molecular weight of 32,000 in surface extracts of the strains. The expression of the adhesion was dependent on culture medium and temperature, and the adhesion was D-mannose resistant. Antisera raised against the 32,000-molecular-weight protein inhibited adhesion. This adhesion was not expressed in two nonpathogenic O103 strains, indicating its implication in virulence. However, the same adhesin was expressed by two O128 non- or moderately pathogenic strains. Therefore, adhesion to enterocytes is not the only factor involved in the pathogenicity of O103 strains.

Construction and analysis of TnphoA mutants of enteropathogenic Escherichia coli unable to invade HEp-2 cells

Enteropathogenic Escherichia coli (EPEC) strains have recently been shown to invade tissue culture cells. We describe a set of 22 Tn5 IS50L::phoA (TnphoA) insertion mutants of EPEC strain E2348-69 that are unable to invade HEp-2 cells. Each mutant was tested for the ability to adhere to and to induce the polymerization of actin in HEp-2 cells. Southern hybridization of plasmid and total DNA of each strain was performed to determine the location of each TnphoA insert, and each TnphoA insert along with flanking EPEC sequences was cloned. These studies resulted in the grouping of the mutants into five main categories. These include strains with plasmid and chromosomal insertions that alter adherence, chromosomal insertions that alter the ability to induce actin polymerization, and chromosomal insertions that do not affect adherence or actin polymerization. These studies indicate that genes affecting EPEC adherence may be located on both the plasmid and chromosome, that several genes are involved in the induction of actin polymerization in epithelial cells, and that EPEC invasion is a complex process involving multiple genetic loci.

Microbiologic and clinical evidence supporting the role of Aeromonas caviae as a pediatric enteric pathogen

Aeromonas caviae was recovered as the sole potential enteric pathogen from the stools of 14 of 17 symptomatic children (10 younger than 1 year of age) while Aeromonas hydrophila, Aeromonas sobria, and Plesiomonas shigelloides were isolated once each. The infants from whom A. caviae was isolated all presented with a watery diarrhea lasting 1 to 3 weeks. None of these infants was breast-fed, and all had a stool pH of greater than 7.5. All of the A. caviae isolates, including a reference strain (ATCC 15468), adhered to HEp-2 cells, and preliminary data showed that they produced a cytotoxin as well. Because A. caviae can survive at an elevated pH, as found in the gastrointestinal tract of formula-fed infants, and because of the adherence and cytotoxin production capabilities of the species, it should be regarded as an enteric pathogen in pediatric patients and most probably among adults as well.

Comparison of two assay methods for patterns of adherence to HEp-2 cells of Escherichia coli from patients with diarrhea

To determine whether methodological differences in the HEp-2 adherence assay could explain conflicting results of field studies, 244 strains of Escherichia coli from Mexican children with diarrhea were tested for patterns of adherence by the method used at the Center for Vaccine Development, University of Maryland (CVD), and at the Center for Infectious Diseases, University of Texas Medical School and School of Public Health (UTH). The CVD assay differentiated three phenotypes of adherent E. coli, including localized, diffuse, or aggregative adherence (LA, DA, or AA, respectively). There was agreement on pattern of adherence in 241 of the 244 strains (98.8%) tested by the CVD method in both Baltimore and Houston, and AA+ was the most common phenotype (28.5% of isolates). Among these isolates, the UTH assay detected only two adherent phenotypes (LA and DA), since it did not distinguish the AA pattern. The LA+ strains detected by each assay were compared for positivity with the enteropathogenic E. coli adherence factor (EAF) gene probe. Of the 16 strains LA+ by the CVD method, 100% were EAF+; in contrast, only 11 of 22 strains LA+ by the UTH method were EAF+ (P = 0.00074). These results help explain why in pediatric field studies in Mexico where isolates were tested by the UTH method (J. J. Mathewson, R. A. Oberhelman, H. L. Dupont, F. J. de la Cabada, and E. V. Garibay, J. Clin. Microbiol. 25:1917-1919, 1987) LA+ strains often did not belong to enteropathogenic E. coli O serogroups and why the AA pattern was not observed; the opposite was found in studies of pediatric diarrhea in Chile in which the CVD assay was used (M. M. Levine, V. Prado, R. M. Robins-Browne, H. Lior, J. B. Kaper, S. Moseley, K. Gicquelais, J. P. Nataro, P. Vial, and B. Tall, J. Infect. Dis. 158:224-228, 1988). Since it appears that both assays identify E. coli strains associated with diarrheal illness, the genetic relationships among these strains should be examined in future studies.

Adhesion of enterotoxigenic Escherichia coli to the human colon carcinoma cell line Caco-2 in culture

Enterotoxigenic Escherichia coli (ETEC) strains possessing colonization factor antigen I (CFA/I), CFA/II, CFA/III, and antigen 2230 were tested for their ability to adhere to the following cell lines: HeLa, HEp-2, HRT 18, Hutu 80, MDBK, MDCK, Vero, and Caco-2. ETEC strains adhered only to the Caco-2 cell line. Irrespective of the known adhesive factors, the ETEC strains that adhered to the brush border of human enterocytes also adhered to the Caco-2 cell line. The negative variants, which were cured of the plasmid encoding the adhesive factor, did not adhere. Adhesion of ETEC strains no longer occurred when the Caco-2 cells were pretreated with the homologous colonization factor antigen or when the bacterial cells were pretreated with homologous antibodies raised against the adhesive factors. This indicates that this adhesion is specific and that a different receptor exists for each type of adhesion factor. Electron micrographs of cross sections of the monolayer showed that the adhesion of ETEC strains to the brush border microvilli does not induce any lesion. Therefore, the Caco-2 cell line behaves in the same way as human enterocytes do.

Identification of plasmid-encoded mannose-resistant hemagglutinin and HEp-2 and HeLa cell adherence factors of two diarrheagenic Escherichia coli strains belonging to an enteropathogenic serogroup

Two Escherichia coli strains (B/M 369 and C-35) belonging to enteropathogenic serogroup O86 were isolated from patients with infantile diarrhea and studied with respect to their cellular adherence properties. Both strains exhibited adherence (Ad+) to HEp-2 and HeLa cell monolayers in vitro and expressed mannose-resistant hemagglutinating (MRHA+) activity towards human, chicken, and sheep (but not mouse, rabbit, or guinea pig) erythrocytes. Cellular adherence properties of both strains could be substantially reduced by pronase treatment and by heat treatment (100 degrees C for 5 min) of bacteria. Electron microscopic examination failed to reveal fimbria- or pilus-like structures on the bacterial cell surface. Conjugation experiments conducted with these strains suggested that both MRHA and HEp-2 and HeLa cell adherence factors were encoded by the same plasmid, with a size of 55 to 57 megadaltons (MDa). Further biochemical studies indicated that the cellular adherence factors were associated with cell surface structures of bacteria that were proteinaceous in nature. An antiserum, rendered specific for the 57-MDa plasmid (pRP201) products of B/M 369 by adsorption, reacted with both MRHA+ Ad+ strains, B/M 369 and C-35, but not with their 57- or 55-MDa plasmidless MRHA- Ad- transconjugants or with other MRHA- Ad- E. coli strains. Immunological studies showed that the absorbed antiserum recognized two proteins with subunit molecular sizes of 18 and 14.5 kDa that were present on the cell surfaces of both strains. Furthermore, the absorbed antiserum at subagglutinating dilutions did inhibit, although only partially, the MRHA and HEp-2 and HeLa cell adherence activities of both E. coli strains. All these results would indicate that some of the E. coli strains belonging to enteropathogenic serogroups express their adherence potential through factors that were hitherto unrecognized.

Nationwide surveillance program to identify diarrhea-causing Escherichia coli in children in Thailand

Escherichia coli strains isolated from children with diarrhea were collected from 16 hospitals in different districts in Thailand during 1985 and 1986 and submitted to the National Reference Laboratory. Isolates were identified by serogrouping or as enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC) adhesin factor (EAF) E. coli, or Shiga-like-toxin (SLT)-producing E. coli by DNA hybridization. EPEC strains of known serogroups were isolated from 10%, ETEC strains were isolated from 6%, EAF E. coli strains were isolated from 4%, EIEC strains were isolated from less than 1%, and SLT-producing E. coli strains were isolated from none of 393 children with diarrhea. Among 278 children whose ages were recorded, the highest rate of isolation of EAF E. coli was 11% (9 of 85) from children less than 6 months old. ETEC was isolated from 5% (4 of 85) of children less than 6 months old, from 10% (12 of 118) of children 6 to 23 months old, and from 1% (1 of 75) of children greater than 23 months old. EPEC strains of known serogroups were isolated from 18% (15 of 85) of children less than 6 months old, from 11% (13 of 118) of children 6 to 23 months old, and from 9% (7 of 75) of children greater than 23 months old. E. coli strains that hybridized with the EIEC probe were isolated from three children who were 20, 36, and 48 months old. Examining E. coli for hybridization with DNA probes for virulence determinants is a practical way of conducting nationwide surveillance of diarrhea-causing E. coli. Since only 33% (13 of 39) of EPEC serogroups hybridized with the EAF probe and none hybridized with the SLT probes, identification of EPEC by serogroups analysis, followed by serotyping, should continue to be used in the identification of EPEC.

Adhesion to cells in culture and plasmid profiles of enteropathogenic Escherichia coli isolated from outbreaks and sporadic cases of infant diarrhoea

Enteropathogenic strains of Escherichia coli (EPEC) that caused 10 outbreaks of infant diarrhoea in the U.K. between 1968 and 1986 were studied. All gave localised adherence (LA) to HEp-2 cells, HeLa cells and Intestine 407 cells in culture. All hybridised with the EPEC adherence factor (EAF) probe. The hybridising sequences were carried on plasmids ranging in size from 26 to 76 MDa. EPEC from sporadic cases of infant diarrhoea occurring between 1979 and 1986 that belonged to the same serotypes as the outbreak strains were also studied. All strains of serotypes O111ab.H2, O114.H2, O119.H6, O127.H6 and O142.H6 gave LA and were EAF-positive. In other serotypes, non-adhering strains or strains giving diffuse adherence were found also. In addition, strains of serotype O128.H2 which gave LA but did not hybridise with the EAF probe were identified. The strains isolated from sporadic cases of diarrhoea in the U.K. were similar, with respect to adhesion and hybridisation, to those isolated from sporadic cases of diarrhoea in developing countries.

Colonization of neonates in a nursery ward with enteropathogenic Escherichia coli and correlation to the clinical histories of the children

Stool samples were examined from 30 preterm neonates admitted to a nursery ward; 16 neonates had diarrhea, 12 constituted an age-matched control group without diarrhea, and 2 had an unknown history regarding diarrhea. Variable numbers of enteropathogenic Escherichia coli serotype O111:HNT strains possessing the gene coding for the enteroadherence factor (EAF) were found in stool samples from 13 of the neonates. No other microbiological enteropathogen was found. A total of 294 strains (9 or 10 from each neonate, comprising 229 E. coli and 65 Klebsiella pneumoniae strains) were characterized with respect to plasmid content and grouped into 37 plasmid profile groups. Diarrhea was found not to be correlated with any specific plasmid profile or with the presence of the EAF-positive strains but rather with the number of strains with one specific plasmid profile or with the number of EAF-positive strains (of the 9 or 10 strains) isolated from each stool sample. All the neonates who died had diarrhea (5 died of 16 with diarrhea); all five of the neonates who died possessed strains with one specific plasmid profile group, and EAF-positive strains were isolated from four of them. Of the seven neonates from whom seven or more EAF-positive isolates were isolated, three died, compared with only one of five of those from whom only a few (1 to 3 of 10) EAF-positive strains were isolated. Both plasmid profiling and genetic probing with the EAF probe were found to be good alternatives when serotyping is not available for identification of O111:HNT enteropathogenic E. coli strains.

Adhesive properties of enteropathogenic Escherichia coli isolated from infants with acute diarrhea in Africa

The adhesive properties of 69 enteropathogenic Escherichia coli (EPEC) strains were studied. The strains were isolated from diarrheal stools of infants in Burundi, Africa, and identified by serotyping with 12 classical EPEC O serogroup antisera. A test for adhesion to HEp-2 cells revealed that 52% of the strains showed localized adherence and 13% diffuse adherence. Localized adherence phenotype was found in previously described serogroups O86, O111, O125, O127, O128 and O142; strains belonging to another serogroup, O126, also exhibited localized adherence. Use of an EPEC adherence factor DNA probe in colony hybridization and in Southern blot techniques revealed that all strains exhibiting localized adherence and no strain exhibiting diffuse adherence produced a positive reaction; the genes were localized on high molecular weight plasmids (50-70 megadaltons). In vitro adhesion tests with human enterocytes performed concurrently with all 69 strains showed that only six of them adhered. These strains belonged to the O26, O117, O125, O128 and O142 serogroups. The adhesin CFA/I was detected only in the O128 Escherichia coli. The strain of serogroup O142 exhibited both adhesion to human enterocytes and localized adherence to HEp-2 cells, which suggests that the adhesive systems of enterotoxigenic and enteropathogenic Escherichia coli may coexist.

Serotype, antimicrobial resistance, and adherence properties of Escherichia coli strains associated with outbreaks of diarrheal illness in children in the United States

Since most recorded outbreaks of diarrhea in U.S. infants attributed to Escherichia coli occurred before currently available pathogenicity assays existed, we examined the characteristics of nonenterotoxigenic E. coli strains isolated from 50 outbreaks of diarrheal disease in U.S. infants between 1934 and 1987. We assayed the strains for enteropathogenic E. coli (EPEC) serotype, localized adherence (LA) and diffuse adherence to tissue cultures, the presence of EPEC adherence factor genes, Shiga-like (Vero) toxin production, and antimicrobial resistance. EPEC serotypes were identified in 28 outbreaks (56%). LA to HeLa cells was found in 23 outbreak strains and correlated 100% with the EPEC adherence factor probe. LA was observed in 21 of 28 EPEC and 2 of 22 non-EPEC strains; however, 5 of 23 strains that were LA positive for HeLa cells did not adhere to HEp-2 or HL cells. One strain was diffuse adherence positive, and none was Shiga-like toxin positive. Multiple resistance was common in EPEC (64%), LA-positive (74%), and LA-positive EPEC (76%) strains but not in others (10%). EPEC serotypes or LA was found in 60% (n = 30) of the outbreak strains. The remaining E. coli strains may represent nonpathogenic normal flora, as-yet-undefined pathogens, or pathogens that have lost virulence-associated traits during storage or subculturing.

Virulence factors and biochemical characteristics of serotypes of Escherichia coli serogroup O29

Escherichia coli strains belonging to serogroup O29 were studied. Invasiveness was the most common virulence factor described in this serogroup, but a few papers also reported production of heat-stable (ST) enterotoxin. In the present study invasive ability was found in O29:H- strains, whereas production of ST-I enterotoxin was observed only in serotype O29:H21 strains, showing that virulence was a characteristic of specific serotypes or bioserotypes within the O29 serogroup. Different serotypes were found among strains that were neither invasive nor toxigenic. Invasive strains were biochemically less active than the toxigenic ones and presented the invasiveness plasmid (pINV) of about 120 to 140 megadaltons, whereas hybridization tests showed that ST-I production was related to a plasmid of about 90 megadaltons. A diffuse adherence pattern to HeLa cells was observed in all ST-I isolates, but the role of this adherence in the pathogenicity of these strains was not determined. Thus, a unique biochemical pattern and plasmid profile may be useful characteristics to distinguish between pathogenic (toxigenic or invasive) and nonpathogenic O29 strains.

Molecular characterization of a fimbrial adhesin, F1845, mediating diffuse adherence of diarrhea-associated Escherichia coli to HEp-2 cells

A fimbrial adhesin, designated F1845, was found to be responsible for the diffuse HEp-2 cell adherence of a diarrheal Escherichia coli isolate. The genetic determinant of F1845 was cloned, and the order of the genes necessary for production of F1845 was determined by maxicell analysis. Five polypeptides with apparent sizes of 10, 95, 27, 15.5, and 14.3 kilodaltons (kDa) were found to be encoded in that order by the F1845 determinant. The nucleotide sequence of the 14.3-kDa subunit gene was determined and found to share extensive homology in its signal sequence with the gene encoding the structural subunit of the AFA-1 hemagglutinin of a uropathogenic E. coli strain (A. Labigne-Roussel, M.A. Schmidt, W. Walz, and S. Falkow, J. Bacteriol. 162:1285-1292, 1985) but not in the region encoding the mature protein. Southern blot hybridizations indicated that the F1845 determinants are of chromosomal origin. Hybridization studies using a probe from the region encoding the 95-kDa polypeptide indicated that related sequences may be plasmid associated in some strains and chromosomal in others. Additional hybridization studies of E. coli isolates possessing sequence homology to the F1845 determinant suggest that the sequences in the 5' region of the F1845 structural subunit gene are more highly conserved than sequences in the 3' region.

Properties of Vero cytotoxin-producing Escherichia coli of human and animal origin belonging to serotypes other than O157:H7

Eight non-O157:H7 Vero cytotoxin (VT)-producing Escherichia coli (VTEC) strains isolated from ill persons and nine bovine and lamb strains of serogroups matching the human strains, were characterized for various properties known to be associated with E. coli virulence. Five different serogroups were represented: O5, O55, O103, O111 and O153. The bovine and lamb strains produced VT1, while 3 human strains produced VT1, 3 produced VT2 and 2 were positive for both VT1 and VT2. The strains were non-haemolytic on horse blood agar, did not produce either heat stable toxin A (STA) or heat labile toxin (LT), and were noninvasive. The CVD419 probe which has been proposed to identify enterohaemorrhagic E. coli (EHEC) hybridized with all of the O5 and O103 strains, none of the O55 and O153 strains, and 3 of the 4 O111 strains. The strains carried several different sized plasmids and hybridization of Southern blots with the CVD419 probe identified plasmids ranging in size from 42 x 10(6) to 90 x 10(6). The strains did not hybridize with the enteroadherence factor (EAF) probe derived from an enteropathogenic strain and associated with the ability to give localized adherence to HEp-2 cells. Nevertheless five of the strains adhered in a localized pattern to HEp-2 cells and Intestine 407 cells. Adhesion to either HEp-2 or Intestine 407 cells did not correlate with hybridization with the CVD419 probe or haemagglutinating properties.

The association of enterotoxigenic and enteropathogenic Escherichia coli and other enteric pathogens with childhood diarrhoea in Yugoslavia

The presence of enterotoxigenic and enteropathogenic Escherichia coli (ETEC and EPEC, respectively) was investigated in stool specimens of 1082 preschool children with diarrhoea and in stools of 335 healthy controls in localities in southern Yugoslavia, as well as in 566 children with diarrhoea and in 231 controls living in northern part of the country, during the seasonal peak (August-November) of enteric diseases in 1986. ETEC were found in 114 (10.5%) children with diarrhoea and in 14 (4.2%) controls (P less than 0.001) in the southern part, and in 26 (4.6%) ill children and one (0.4%) well child (P less than 0.005) in the northern part of Yugoslavia. EPEC were isolated from stools of 85 (7.9%) children with diarrhoea and of 14 (4.2%) well children (P less than 0.05) in localities of southern Yugoslavia, and from 22 (3.9%) ill children and from 10 (4.3%) controls in northern Yugoslavia. Nineteen EPEC strains expressed localized adherence to HEp-2 tissue culture cells; all were isolated from stools of ill children. In southern Yugoslavia, where other enteropathogens were sought, the most commonly found agents in ill children were shigellae (17.5%), rotavirus (11.8%), ETEC, and EPEC. Potential pathogens were detected in 44.5% cases of sporadic diarrhoea and in 15.8% controls. This study revealed that ETEC were associated with acute diarrhoeal disease in Yugoslav preschool children. On the other hand, the diagnosis of EPEC-diarrhoea by routine determination of serogroup established the association of these agents with sporadic diarrhoea only in the 0-2 years age categories in all investigated localities. In the less developed southern part of Yugoslavia bacteria were the predominant causative agents of enteric illness during the seasonal peak of this disease.

Enteropathogenic Escherichia coli serotype O111:HNT isolated from preterm neonates in Nairobi, Kenya

This investigation was initiated as a consequence of several cases of diarrhea in a nursery ward for preterm babies in Nairobi, Kenya. Ten lactose-positive colonies were isolated from the stools of each of 30 neonates, regardless of whether they had diarrhea; 229 strains were identified as Escherichia coli and 65 strains were identified as Klebsiella pneumoniae. Six strains were lost during laboratory handling. No other bacterial, viral, or parasitic enteropathogens were identified. Using synthetic alkaline phosphatase-labeled probes, the bacterial isolates were found to be negative for the presence of genes coding for heat-stable and heat-labile enterotoxins. Seventy-eight E. coli strains isolated from a total of 13 neonates possessed the E. coli enteropathogenic adhesion factor (EAF) gene, as demonstrated by the use of a cloned radiolabeled DNA fragment probe. These strains possessed similar plasmid profiles constituting a core plasmid profile, and while all adhered to HeLa cells, none produced Vero cell cytotoxins. The EAF gene was located on a 65-megadalton plasmid. Serotyping showed the strains to be of serogroup O111 and serotype H nontypable, a well known enteropathogenic type. Five neonates died during the outbreak, and the fatality rate was 30.7% (4 of 13) for neonates infected with EAF-positive E. coli strains compared with 7.7% (1 of 13) for neonates from whom only EAF-negative E. coli strains were isolated. K. pneumoniae only was isolated from five neonates.

Cloning and expression of an adhesin (AIDA-I) involved in diffuse adherence of enteropathogenic Escherichia coli

The adherence of enteropathogenic Escherichia coli (EPEC) to the small bowel mucosa is an important step in the pathogenesis of diarrheal diseases. It has been shown that many EPEC strains adhere to HEp-2 and especially HeLa cells in characteristic patterns termed localized adherence (LA) and diffuse adherence (DA). A plasmid-derived DNA fragment encoding a factor specific for LA hybridized only to EPEC strains expressing LA, which demonstrated that LA and DA are mediated by two genetically distinct adhesins. EPEC strain 2787 (O127:H27), isolated from a case of infantile diarrhea, exhibited three major properties: (i) it showed DA to HeLa cells, (ii) it carried two large (ca. 100-kilobase [kb]) plasmids and one small plasmid of about 3 kb, and (iii) no fimbriae could be detected by electron microscopy in organisms grown on agar plates or in liquid cultures. Whole isolated plasmid DNA was partially digested with EcoRI and cloned into the vector pBR322. One recombinant clone (pIB6) was found to exhibit the same DA pattern on HeLa cells as did the parent strain. This clone contained an 11-kb DNA fragment derived from the largest of the three plasmids, as shown by Southern hybridization. By deletion analysis, a 6.0-kb DNA fragment was shown to be sufficient for expression of the DA phenotype. This insert encoded the production of a 100,000-dalton protein mediating adhesion to HeLa cells.

Prevalence of Escherichia coli strains with localized, diffuse, and aggregative adherence to HeLa cells in infants with diarrhea and matched controls

To determine the possible role of Escherichia coli strains with three different patterns of adherence to HeLa cells in causing diarrhea in infants in São Paulo, Brazil, we studied stool specimens from 100 infants up to 1 year of age with acute diarrheal illnesses and 100 age-matched control infants without recent diarrhea. E. coli with localized adherence to HeLa cells was much more common in patients (23%) than in controls (2%) (P less than 0.0001) and was detected more frequently than rotavirus (19%) was in patients, even though the study was conducted during the coldest months of the year. Most (80%) of the E. coli colonies with localized adherence were of traditional enteropathogenic E. coli serotypes. Little difference was found between patients and controls in the rate of isolation of E. coli with diffuse adherence (31 and 32%, respectively) or aggregative adherence (10 and 8%, respectively). A genetic probe used to detect a plasmid-mediated adhesin which confers expression of localized adherence proved to be 100% sensitive and 99.9% specific in detecting E. coli with localized adherence to HeLa cells. Although E. coli strains with localized adherence have now been shown to be enteric pathogens in several parts of the world, the role of strains showing diffuse adherence and aggregative adherence is still uncertain.

Determination by DNA hybridization of Shiga-like-toxin-producing Escherichia coli in children with diarrhea in Thailand

Specific DNA probes were used to identify Shiga-like-toxin (SLT) I- and II-producing Escherichia coli from children less than 5 years of age with bloody diarrhea, in infants with diarrhea, and in controls of the same age without diarrhea in Thailand. At one hospital, SLT-producing E. coli was identified in 4 (7%) of 54 children with bloody diarrhea from whom other enteric pathogens were not identified and from 3 (6%) of 50 children without diarrhea. In the positive specimens, SLT-producing E. coli constituted only 0.3 to 4% of the 100 to 300 colonies on the replica blots. Non-toxin-encoding 933J and 933W bacteriophagelike DNA sequences were detected by colony hybridization with E. coli isolates from 18 (33%) of 54 children with bloody diarrhea and 23 (46%) of 50 controls. At another hospital, SLT-producing E. coli was not identified in 115 infants with diarrhea and 119 controls without diarrhea. One infant with diarrhea was infected with E. coli O76:H7 that hybridized with the enterohemorrhagic E. coli probe but not with the SLT probes. E. coli producing SLT I or SLT II was isolated in small numbers from a similar proportion of Thai children with bloody diarrhea in whom no other enteric pathogen was identified and from controls without diarrhea.

Examination of colonies and stool blots for detection of enteropathogens by DNA hybridization with eight DNA probes

We compared three methods for detecting enteropathogens in 416 children with diarrhea: (i) examination of 10 lactose-fermenting and all non-lactose-fermenting Escherichia coli (colony blots); (ii) examination of 300 colonies (replicate blots); and (iii) determination of the total bacterial growth of stools (stool blots). All specimens were spotted onto Whatman 541 filters and hybridized with specific radiolabeled DNA probes. Enterotoxigenic E. coli was detected in 38 patients by examining colony blots, in 52 patients by examining replicate blots, and in 45 patients by examining stool blots. Enteropathogenic E. coli adhesin factor was detected in 12 patients by colony blots, in 25 patients by replicate blots, and in 16 patients by stool blots. E. coli that hybridized with the enterohemorrhagic E. coli probe was detected in 2 patients by colony blots, in 11 patients by replicate blots, and in 0 patients by stool blots. Shiga-like toxin-producing E. coli was detected in 0 patients by colony blots, in 12 patients by replicate blots, and in 0 patients by stool blots. Shigella spp. were identified by standard bacteriological methods in 82 patients, and enteroinvasive E. coli was identified by colony blots in 11 patients (total, 93), by replicate blots in 56 patients, and by stool blots in 35 patients. Of 82 culture-confirmed Shigella infections, 45 were identified by examining replicate blots with the 17-kilobase-pair probe and 36 were identified by examination with the Ipa probe (P less than 0.05). Examining replicate blots with specific probes identified more enterotoxigenic E.coli (P < 0.005), enteropathogenic E.coli adhesion factor-producing E.coli (P < 0.001), and Shiga-like toxin-producing E.coli (P < 0.005) infections than examining colony blots. More Shigella and enteroinvasive E.coli infections were identified by standard bacteriological methods and examining colony blots with a specific probe than by examining replicate and stool blots (P < 0.001).

Infection by verocytotoxin-producing Escherichia coli

Verocytotoxin (VT)-producing Escherichia coli (VTEC) are a newly recognized group of enteric pathogens which are increasingly being recognized as common causes of diarrhea in some geographic settings. Outbreak studies indicate that most patients with VTEC infection develop mild uncomplicated diarrhea. However, a significant risk of two serious and potentially life-threatening complications, hemorrhagic colitis and the hemolytic uremic syndrome, makes VTEC infection a public health problem of serious concern. The main reservoirs of VTEC appear to be the intestinal tracts of animals, and foods of animal (especially bovine) origin are probably the principal sources for human infection. The term VT refers to a family of subunit exotoxins with high biological activity. Individual VTEC strains elaborate one or both of at least two serologically distinct, bacteriophage-mediated VTs (VT1 and VT2) which are closely related to Shiga toxin and are thus also referred to as Shiga-like toxins. The holotoxins bind to cells, via their B subunits, to a specific receptor which is probably the glycolipid, globotriosyl ceramide (Gb3). Binding is followed by internalization of the A subunit, which, after it is proteolytically nicked and reduced to the A1 fragment, inhibits protein synthesis in mammalian cells by inactivating 60S ribosomal subunits through selective structural modification of 28S ribosomal ribonucleic acid. The mechanism of VTEC diarrhea is still controversial, and the relative roles of locally acting VT and "attaching and effacing adherence" of VTEC to the mucosa have yet to be resolved. There is increasing evidence that hemolytic uremic syndrome and possibly hemorrhagic colitis result from the systemic action of VT on vascular endothelial cells. The role of antitoxic immunity in preventing the systemic complications of VTEC infection is being explored. Antibiotics appear to be contraindicated in the treatment of VTEC infection. The most common VTEC serotype associated with human disease is O157:H7, but over 50 different VT-positive O:H serotypes have now been identified. The best strategies for diagnosing human VTEC infection include testing for the presence of free VT in fecal filtrates and examining fecal cultures for VTEC by means of deoxyribonucleic acid probes that specify genes encoding VT1 and VT2. Both methods are currently confined to specialized laboratories and await commercial development for wider use. In the meantime, most laboratories should continue to screen for the most common human VTEC serotype, O157:H7, using a sorbitol-containing MacConkey medium.

In vitro model for Campylobacter pylori adherence properties

The adherence of 12 strains of Campylobacter pylori was studied on four cell lines. Immunofluorescence and scanning and transmission electron microscopy were used to visualize the bacteria. A heavy adherence to the epithelial cell line HEp-2 and to the intestinal cell line Int-407 was noted. By transmission electron microscopy, a close association between bacteria and cells in the form of cup-like structures was observed, but pedestals were not present.