Close association of verotoxin (Shiga-like toxin) production with enterohemolysin production in strains of Escherichia coli

Comparison between a PCR-ELISA test and the vero cell assay for detecting Shiga toxin-producing Escherichia coli in dairy products and characterization of virulence traits of the isolated strains

AIMS

This paper provides information on a PCR-ELISA method for detecting Shiga toxin-producing Escherichia coli (STEC), and on their prevalence in dairy products.

METHODS AND RESULTS

The sensitivity and specificity of the test was evaluated using pure cultures, spiked and naturally-contaminated samples. A comparative study with vero cytotoxicity testing was conducted, and STEC isolated from naturally-contaminated samples were characterized. The PCR-ELISA test was highly specific and sensitive, and detected 14% more positive samples than the vero cell assay. The prevalence of STEC in raw milk and unpasteurized cheese was 21.5% and 30.5%, respectively, while samples from the 'dairy environment' and from pasteurized cheese were less contaminated. The 34 strains of STEC isolated from natural samples showed that some of them carried virulence genes.

CONCLUSION

No conclusion can be drawn at the moment concerning the potential risk to consumers.

SIGNIFICANCE AND IMPACT OF THE STUDY

These data show the necessity of valuable screening methods to appreciate the virulence of STEC.

The detection of Shiga toxin-producing Escherichia coli in diagnostic bovine faecal samples using vancomycin-cefixime-cefsulodin blood agar and PCR

The prevalence of complex Shiga toxin-producing Escherichia coli (STEC), i.e. STEC containing accessory virulence factors intimin (eaeA) and/or enterohaemorrhagic E. coli haemolysin (ehxA) and their serotypes were determined in diagnostic bovine faecal samples processed during a 3 months period. The presence of complex STEC was determined using PCR and vancomycin-cefixime-cefsulodin blood agar (BVCCA) using a dual approach which involved (i) direct culture of faecal samples on BVCCA followed by mutiplex PCR of BVCCA positive colonies and (ii) culture of faecal samples enriched in modified EC (mEC) broth (with a complex STEC profile determined by PCR) on BVCCA followed by multiplex PCR of BVCCA positive colonies. Using both techniques complex STEC were isolated from 23 (18.7%) of the 123 faecal samples. Complex STEC were isolated from 14 faecal samples by direct culture on BVCCA and 13 faecal samples yielded complex STEC by culture of mEC broths with a complex STEC profile on BVCCA. Only four samples were positive using both techniques. The serotypes isolated included O5:H-, O26:H-, O26:H11, O91:H21, O111:H-, O111:H8, O104:H11, O113:H21 and O157:H8. This study confirms that non-O157 STEC can be isolated from bovine faeces and that they carry types associated with human disease. This work also demonstrates that the use of a dual approach is advisable to increase the likelihood of isolating complex STEC.

Occurrence of Escherichia coli O157 in Finnish cattle

Bovine faecal samples were collected during June-December 1997 at 14 major abattoirs slaughtering cattle in Finland. Escherichia coli O157 was isolated from 19 of the 1448 samples (1.31%) after enrichment and immunomagnetic separation (IMS). The positive faecal isolates originated from 16 farms and eight abattoirs. The occurrence of E. coli O157 was highest in July (8/204; 3.92%) and September (6/244; 2.46%). No E. coli O157 was detected in November and December, nor from the faecal samples from the northernmost region where cattle density is low. All of the isolates carried the eae gene and showed the enterohaemolytic phenotype. All except one were motile and had the flagella antigen H7. Seventeen of the isolates were positive for stx(2) gene and one carried both the stx(1) and stx(2) genes. Of the 17 isolates with stx genes, 16 were verocytotoxin-positive in a reversed passive latex agglutination test after polymyxin extraction but only eight without extraction. The isolates belonged to 10 different pulsed-field gel electrophoresis (PFGE) patterns. The most common PFGE pattern (1.42) was detected in eight isolates (42.1%). Four PFGE patterns (1.1; 1.6; 1.12; 1.14) were identical with those isolated from humans in Finland, suggesting that at least some human E. coli O157 infections may be of bovine origin.

Prevalence, antibiotic susceptibility, and diversity of Escherichia coli O157:H7 isolates from a longitudinal study of beef cattle feedlots

Prevalence, antibiotic susceptibility, and genetic diversity were determined for Escherichia coli O157:H7 isolated over 11 months from four beef cattle feedlots in southwest Kansas. From the fecal pat (17,050) and environmental (7,134) samples collected, 57 isolates of E. coli O157:H7 were identified by use of bacterial culture and latex agglutination (C/LA). PCR showed that 26 isolates were eaeA gene positive. Escherichia coli O157:H7 was identified in at least one of the four feedlots in 14 of the 16 collections by C/LA and in 9 of 16 collections by PCR, but consecutive positive collections at a single feedlot were rare. Overall prevalence in fecal pat samples was low (0.26% by C/LA, and 0.08% by PCR). No detectable differences in prevalence or antibiotic resistance were found between isolates collected from home pens and those from hospital pens, where antibiotic use is high. Resistant isolates were found for six of the eight antibiotics that could be used to treat E. coli infections in food animals, but few isolates were multidrug resistant. The high diversity of isolates as measured by random amplification of polymorphic DNA and other characteristics indicates that the majority of isolates were unique and did not persist at a feedlot, but probably originated from incoming cattle. The most surprising finding was the low frequency of virulence markers among E. coli isolates identified initially by C/LA as E. coli O157:H7. These results demonstrate that better ways of screening and confirming E. coli O157:H7 isolates are required for accurate determination of prevalence.

Genetic analysis for virulence factors in Escherichia coli O104:H21 that was implicated in an outbreak of hemorrhagic colitis

Isolates of enterohemorrhagic Escherichia coli (EHEC) of serotype O104:H21 implicated in a 1994 outbreak of hemorrhagic colitis in Montana were analyzed for the presence of trait EHEC virulence markers. By using a multiplex PCR that specifically amplifies several genes, the O104:H21 strains were found to carry only the Shiga toxin 2 gene (stx2) and to express Stx2. They did not have the eaeA gene for gamma-intimin, which is typically found in O157:H7, or the alpha- or beta-intimin derivatives, which are common in other EHEC and enteropathogenic E. coli serotypes. Results of the multiplex PCR also indicated that the ehxA gene for enterohemolysin was absent from O104:H21. This, however, was not consistent with the results of a phenotypic assay that showed them to be hemolytic or a PCR analysis with another set of ehxA-specific primers, which indicated the presence of ehxA. To resolve this discrepancy, the ehxA region in O104:H21 and O157:H7 strains, to which the multiplex PCR primers anneal, was cloned and sequenced. Comparison of the sequences showed that the upstream primer binding site in the ehxA gene of O104:H21 was not identical to that of O157:H7. Specifically, there were several base mutations, including an A-to-G substitution at the 3' end of the primer binding site. These base mutations are presumably not unique to O104:H21, since other enterohemolytic serotypes were also not detected with the ehxA primers used in the multiplex PCR. Comparison of the ehxA sequences of O104:H21 strains with those of other Stx-producing E. coli strains showed that they more closely resembled those of O8:H19 strains, which have cluster II ehxA genes, than those of O157:H7 strains, which have cluster I ehxA sequences. By modifying the upstream ehxA primer, the multiplex PCR was able to detect ehxA genes in both O157:H7 and O104:H21 strains.

Lactate dehydrogenase release assay from Vero cells to distinguish verotoxin producing Escherichia coli from non-verotoxin producing strains

The Vero cell assay presently used for virulence testing of verotoxigenic Escherichia coli (VTEC) requires at least 48-96 h where cytotoxicity effects are examined under a microscope. Here, a complimentary rapid assay was developed that measures endogenous lactate dehydrogenase (LDH) release from Vero or HEp-2 cells as an indicator of cytotoxicity. Toxin preparations from 24 VTEC strains induced 36-89% LDH from Vero cells and 15-62% LDH from HEp-2 cells in 12-16 h. A verotoxin-positive but enterohemolysin negative strain also showed a similar cytotoxicity effect. In contrast, three VT-negative strains caused only 13-16% LDH from Vero cells and 1-7% LDH from HEp-2 cells. Five presumptive E. coli isolates from naturally contaminated food and clinical sources did not induce significant LDH release from either cell lines. PCR analysis confirmed the presence of vt1 or vt2 genes in E. coli showing positive LDH values. Similarly, RiboPrinter analysis confirmed and identified the test strains as E. coli except for two meat isolates, which were identified as Hafnia alvei. Cytopathic effects of toxin preparations from VTEC revealed severe lysis, vacuole formation and death in Vero cells and multiple vacuoles and cell elongation in HEp-2 cells. The colorimetric cytotoxicity assay described here can provide quantitative data for determining the virulence potential of verotoxigenic E. coli in 12-16 h.

Characterization of shiga toxin-producing Escherichia coli strains isolated from calves in Poland

Fecal samples from 67 3-5-months-old calves with diarrhea were screened for the presence of shiga toxin-producing Escherichia coli (STEC). Several accessory virulence factors genes were also tested. Among 192 E. coli isolates tested, 15 (7.6%) were found to harbour the shiga toxin 1 or 2 (stx1 or stx2) genes. The stx2-carrying samples were further subtyped by PCR for the stx2c, stx2d, and stx2e toxin variants. It was shown that stx2-positive bacteria mainly possessed the stx2c shiga toxin type gene. The enterohemolysin (hlyA) and intimin (eae) genes were found in seven (46.7%) STEC strains whereas the cytotoxic necrotizin factor 1 and 2 or the P fimbrial genes were detected in two isolates only. This study confirmed that calves are a reservoir of STEC strains (with all pathogenicity genes) that may be virulent for humans.

[Verotoxin-producing Escherichia coli infections: study of its prevalence in children in the Auvergne region]

Verotoxin producing Escherichia coli (VTEC) have been associated with disease outbreaks of diarrhea hemorrhagic colitis and hemolytic-uremic syndrome in humans. Contamination occurs mainly by ingestion of beef and dairy products, but water and person to person transmission have also been described. Most of the clinical signs are due to the production of Stx1 and/or Stx2 Shiga toxins, also called verotoxins. Other virulence factors include enterohemolysin, and the product of the eae gene, intimin, involved in the attaching and effacing adherence phenotype. The predominant serotype is O157:H7, but VTEC strains of more than one hundred serotypes can cause human disease. In order to determine the prevalence of VTEC infections among children in the central part of France, stool samples from hospitalized children were examined for stx1 and stx2 genes by using a polymerase chain reaction (PCR) technique. From October 1997 to September 1998, 658 stool samples were analysed: among them 19 (3%) were stx-PCR positive. Only 8 children out of 19 had diarrhea, and for 5 of them, an enteric pathogen other than VTEC was isolated. VTEC strains were isolated from 10 samples: most of the isolates did not produce verotoxins at a high level, and they did not belong to serotypes associated with pathogenicity, which might explain the absence of relationship between VTEC isolation and pathogenicity in our study.

Prevalence and characteristics of verotoxin-producing Escherichia coli (VTEC) in stool samples from asymptomatic human carriers working in the meat processing industry in Switzerland

A total of 5590 stool samples from healthy employees in the meat industry were screened by PCR for verotoxin-producing Escherichia coli (VTEC). The PCR product of VT-encoding genes was detected in 3. 5% of the samples. Phenotypic and genotypic traits of 47 VTEC strains isolated from asymptomatic carriers were characterized. A variety of serotypes was found; one strain belonged to the serotype O157:H7. The majority of the isolates proved to be VT2-positive. Fifty-seven percent of the verotoxin-producing strains harboured the genes for one or several additional virulence associated factors, including intimin (eae, 8.5%), the 60 MDa plasmid (42.5%), enterohaemolysin (EHEC-hlyA, 38.3%), the heat-stable enterotoxin (astA, 6.4%), a serin protease (espP, 6.4%), colicin production (col D157, 12.8%) and a secretion system II (etpD, 10.6%). None of the strains was positive for a specific enzyme with catalase-peroxidase activity (katP).

Isolation of shiga toxin-producing Escherichia coli (STEC) from foods using EHEC agar

Enterohaemorrhagic Escherichia coli (EHEC) agar was evaluated for its ability to recover one isolate of each of three serotypes (O157:H7, O26 and O113:H21) of shiga toxin-producing E. coli (STEC) from raw mince, pasteurized milk and salami after enrichment. The method detected around one colony-forming unit (cfu) in 25 ml in milk, but was less sensitive with salami, requiring 10-1000 cfu 25 g-1 (depending on serotype) for detection. In raw minced beef any enterohaemolysin-producing colonies were outnumbered by other colonies and only one of 12 enrichments yielded the inoculum serotype. Additional tests were conducted on 15 retail meat products. One 25-g sample of each product was processed as purchased, while another was inoculated with 157-185 cfu of a cocktail of E. coli O157, O113 and O26 cultures. Recovery was easily achieved with cooked meat products and salami. Recovery from raw minced meat was again difficult, but sometimes possible. Testing more suspect colonies than were tested in this study would presumably increase the sensitivity of the method.

Escherichia coli serotype O15:K52:H1 as a uropathogenic clone

To clarify the clinical and bacteriological correlates of urinary-tract infection (UTI) due to Escherichia coli O15:K52:H1, during a 1-year surveillance period we prospectively screened all 1, 871 significant E. coli urine isolates at the Hospital de la Santa Creu i Sant Pau, Barcelona, Spain, for this serotype and assessed the epidemiological features of community-acquired UTI due to E. coli O15:K52:H1 versus other E. coli serotypes. We also compared the 25 O15:K52:H1 UTI isolates from the present study with 22 O15:K52:H1 isolates from other, diverse geographic locales and with 23 standard control strains (8 strains from the ECOR reference collection and 15 strains of nonpathogenic O:K:H serotypes) with respect to multiple phenotypic and genotypic traits. Although E. coli O15:K52:H1 caused only 1.4% of community-acquired E. coli UTIs during the surveillance period, these UTIs were more likely to present as pyelonephritis and to occur in younger hosts, with similar risk factors, than were UTIs due to other E. coli serotypes. Irrespective of geographic origin, E. coli O15:K52:H1 strains exhibited a comparatively restricted repertoire of distinctive virulence factor profiles (typically, they were positive for papG allele II, papA allele F16, and aer and negative for sfa, afa, hly, and cnf1), biotypes, ribotypes, and amplotypes, consistent with a common clonal origin. In contrast, their antimicrobial resistance profiles were more extensive and more diverse than those of control strains. These findings indicate that E. coli O15:K52:H1 constitutes a broadly distributed and clinically significant uropathogenic clone with fluid antimicrobial resistance capabilities.

Adherence of Escherichia coli serogroup O 157 and the Salmonella typhimurium mutant DT 104 to the surface of Saccharomyces boulardii

The detection of lectin sites for mannose-sensitive adhesion in the outer membrane of Saccharomyces boulardii and the irreversible binding of both enteropathogenic Escherichia coli (EPEC) and salmonellae (serovar Salmonella Typhimurium and Salmonella Enteritidis) provided the motivation to carry out further investigations to find out whether also other enteric bacteria such as entero-haemorrhagic Escherichia coli (EHEC) and the DT 104 mutant of S. Typhimurium have the capacity for binding to the cell wall of this yeast. Reference strains and fresh isolates from clinical cases of EHEC infections as well as salmonellae of the DT 104 mutant were included in this study using the agglutination test. The results first of all showed that EHEC of the serogroup O 157 and the DT 104 mutant of S. Typhimurium were bound to the surface of Saccharomyces boulardii. Because these bacteria do not respond very well to drugs but most of the gastrointestinal infections are caused by them, the use of S. boulardii for treatment and prophylaxis could be an excellent alternative.

Epidemiology and diagnosis of Shiga toxin-producing Escherichia coli infections

Shiga toxin-producing Escherichia coli (STEC) have been identified as a worldwide cause of serious human gastrointestinal disease and the life-threatening hemolytic uremic syndrome. The most common serotype implicated is E. coli O157: H7, but infections involving various non-O157 serotypes have been found with increasing frequency in many countries. Food-borne outbreaks caused by STEC can affect large numbers of people and cause serious morbidity, making the bacteria one of the most important emerging pathogens. Because there is no specific treatment of the disease currently available, there is an urgent need for effective preventive measures based on a detailed understanding of the epidemiology of STEC infections. Such measures will also be dependent on the availability of rapid, sensitive, and simple procedures for the detection of the pathogens both in human samples and in samples of nonhuman origin such as food. This review summarizes the current knowledge on the epidemiology of STEC infection and presents a survey of laboratory methods currently available for diagnosis of STEC. Special attention is given to new diagnostic procedures for the less readily detectable non-O157 STEC strains and to simple procedures, usually based on commercially available kits, that can be used in routine clinical microbiological laboratories.

Virulence markers in Shiga toxin-producing Escherichia coli isolated from cattle

This study identified potential virulence markers in 93 eae-positive and 179 eae-negative Shiga toxin-producing Escherichia coli (STEC), isolated from a random sampling of healthy cattle in southwestern Ontario. PCR amplification was used to identify genes for enterohemorrhagic E. coli (EHEC)-hemolysin, the EAF plasmid, and bundle-forming pili (Bfp); adherence to HEp-2 cells and to bovine colonocytes, and the fluorescent actin staining (FAS) test were used to characterize interaction of the bacteria with epithelial cells. The EHEC-hemolysin sequences were detected in 98% of eae-positive isolates compared with 34% of eae-negative isolates. All isolates were negative for EAF and bfp sequences. There was 100% correlation between localized adherence (LA) to HEp-2 cells and the FAS test. Forty-eight (52%) of the eae-positive isolates were LA/FAS-positive, whereas none of the 179 eae-negative isolates was positive in either test. Among the eae-negative isolates, 20 (11%) showed diffuse adherence and 5 (2.8%) showed enteroaggregative adherence to HEp-2 cells. Seventy-three percent of the eae-positive isolates adhered to bovine colonocytes, whereas only 26% of 120 eae-negative isolates that were tested adhered. All 13 O157:H7 isolates were positive for eae and EHEC-hemolysin gene sequences, LA/FAS, and adherence to bovine colonocytes. It is concluded that possession of genes for eae and EHEC hemolysin is correlated with the serotype of STEC, that production of EHEC hemolysin was highly correlated with serotypes implicated in human disease, and that none of the potential markers that were examined can be used to predict the potential virulence of an isolate.

Characterization of eae+ Escherichia coli isolated from healthy and diarrheic calves

Strains of Escherichia coli from 101 healthy and 114 diarrheic calves were screened by PCR for the eae (intimin) gene and Shiga toxin genes (stx). Each eae+ and eae/stx+ strain was examined for antimicrobial susceptibility, enterohemolysin activity, and the somatic O antigen was determined. An immunoassay was used to detect Shiga toxin antigens for the eae/stx+ E. coli. Significantly more (p = 0.005) of the healthy calves carried eae+ and eae/stx+ E. coli in their feces when compared to strains from diarrheic calves. Moreover, Shiga toxin antigens were detected significantly more (p = 0.001) often among the eae/stx+ strains from healthy calves when compared to eae/stx+ strains from diarrheic calves. However, significantly more (p = 0.001) of the eae+ and eae/stx+ strains from diarrheic calves were resistant to at least one of the antimicrobials tested, and the strains from diarrheic calves had a significantly (p = 0.05) higher rate of antimicrobial resistance to at least two different antimicrobial classes. No significant difference (p> or =0.05) was detected among the eae+ and eae/stx+ strains from healthy and diarrheic calves for enterohemolysin production. Serogroups O-negative, O5, O26, and O111 were predominate among both healthy and diarrheic calves.

Absence of DNA sequence homology with genes of the Escherichia coli hemB locus in Shiga-toxin producing E. coli (STEC) O157 strains

By molecular cloning of chromosomal DNA of a human faecal Escherichia coli O6:non-motile strain, we identified a 1350-bp DNA segment which is commonly present in laboratory and wild-type E. coli strains but had no homology to DNA of Shiga-toxin producing E. coli O157, O145 and enteropathogens E. coli O55 strains. The nucleotide sequence of the 1350-bp segment cloned on plasmid pEO67 was determined (GenBank accession number AF087670) and a 97.2% sequence homology was found to a region of the E. coli hemB locus with an unknown gene function. The introduction of pEO67 into an STEC O157:H- strain had a stimulating effect on the growth of the recipient strain which was most expressed when bacteria were grown in iron depleted M9 medium with hemin added as the exogenous iron source. This growth effect was not observed with E. coli K-12 carrying pEO67. We suggest that the cloned gene is involved in iron uptake of E. coli and that the alteration in this part of the hemB locus is clonally inherited in genetically closely related STEC O157 and O55 strains.

Virulence factors and phenotypical traits of verotoxin-producing Escherichia coli strains isolated from asymptomatic human carriers

Fourteen verotoxin-producing Escherichia coli strains isolated from stool samples of 14 different asymptomatic human carriers were further characterized. A variety of serotypes was found, but none of the strains belonged to serogroup O157. Only one isolate carried most of the virulence genes that are associated with increased pathogenicity.

Serodiagnosis of infection with verocytotoxin-producing Escherichia coli

Human sera (167) were screened for antibodies to lipopolysaccharide (LPS) prepared from strains of Verocytotoxin-producing Escherichia coli (VTEC) belonging to a range of serogroups, secreted proteins expressed by attaching and effacing VTEC, enterohaemolysin and H = 7 flagellar proteins. Twelve sera (about 7%) contained antibodies to the LPS of E. coli 05 (one), 026 (two), 0115 (two), 0145 (one), 0163 (one) and 0165 (five). Sera containing antibodies to the LPS of E. coli O26 and O145 also contained antibodies to secreted proteins of 100 and 40 kDa. An additional 34 sera, known to contain antibodies to the lipopolysaccharide of E. coli O157, were examined for antibodies to enterohaemolysin, H = 7 flagellar antigens and bacterial cell surface-associated proteins of 5, 6 and 22 kDa. Three sera contained antibodies to enterohaemolysin and one serum contained antibodies to flagellar proteins. Antibodies to membrane-associated proteins were not detected. It was concluded that enterohaemolysin, H = 7 flagellar proteins and the cell surface-associated proteins were unsuitable for use in immunoassays for providing evidence of infection with VTEC.

Heterogeneity of phenotypic and genotypic traits including organic-acid resistance in Escherichia coli O157 isolates

We undertook an epidemiologic study for the sensitivity of both Shiga-like toxin (Slt)-producing Escherichia coli (STEC) O157 and non-STEC O157 strains isolated from different patients with diarrhea to hydrochloric acid (HCl) and organic acids such as acetate, propionate, butyrate and lactate, and other pathogenic factors. The E. coli O157 isolates examined showed a wide variety of organic-acid susceptibility patterns. E. coli O157 isolates resistant to HCl or acetate were found more frequently than those resistant to other organic acids. These isolates also showed diverse pathogenicity patterns for the presence of the virulence genes, antibiotic susceptibility and plasmid profile.

Hemolytic uremic syndrome in Belgium: incidence and association with verocytotoxin-producing Escherichia coli infection

OBJECTIVE: To evaluate the incidence of hemolytic uremic syndrome (HUS) in Belgium and to determine the role of verocytotoxin-producing Escherichia coli O157:H7 and other serotypes (non-O157 VTEC). METHODS: Twenty-two centers, including the seven university hospitals, registered prospectively all cases of HUS; they collected clinical samples for isolation of VTEC strains and serum for detection of specific O-lipopolysaccharide antibodies. RESULTS: Forty-seven cases of HUS (including five incomplete cases) were recorded. Three cases were seen in non-residents. The incidence of complete HUS in Belgian residents was 4.3 cases/100 000 in children <5 years old, 1.8 cases/100 000 when all children <15 years were considered, and 0.42/100 000 when patients of all ages were taken into account. By combining bacteriologic and serologic results, evidence of VTEC infection was obtained in 64% of the patients, mainly but not exclusively in children with prodromal diarrhea. The 13 VTEC isolates belonged to serotypes O157:H7 (nine isolates), O26:H11, O121:H---, O145:H--- and O172:H--- (one each) and all produced VT2 (+VT2vh-a in three O157 strains) and were positive for the eaeA gene. CONCLUSIONS: The incidence rate found in this study and the high mortality and morbidity linked with this syndrome warrant further registration of pediatric and post-diarrheic adult HUS cases and also examination of stools for both O157 and non-O157 VTEC strains. For effective prevention of this disease, further study of the serotypes and accessory virulence factors associated with HUS is needed.

Bacterial infections of the small intestine and colon

Enterotoxigenic Escherichia coli, Vibrio cholerae O1, Campylobacter jejuni, Salmonella species, and Shigella species are major causes of morbidity and death in diarrheal disease. More recently recognized pathogens are V. cholerae O139 and enterohemorrhagic E. coli. In addition to this, several presumptive virulence factors have been identified in diarrheagenic E. coli and in other species. To confirm these as virulence factors we need good diagnostic tools and good epidemiological studies. These are of vital importance to create vaccines for diarrheal diseases.

Shiga toxin-producing Escherichia coli in finland from 1990 through 1997: prevalence and characteristics of isolates

During the past 10 years Shiga toxin-producing Escherichia coli (STEC) has emerged as one of the most important causes of food-borne infections in industrialized countries. In Finland, with a population of 5.1 million, however, only four STEC O157:H7 infections were identified from 1990 through 1995; the occurrence of non-O157 STEC infections was unknown. In 1996, we established a national prospective study to determine the prevalence of STEC serotypes in feces of Finns with bloody diarrhea. During this enhanced 1-year study period eight sporadic cases of STEC infection were found; of them, only two were indigenously acquired O157:H7 infections. In 1997, O157 infections increased dramatically, with O157 strains causing 51 of all 61 STEC infections. Altogether 14 non-O157:H7 STEC strains were found in Finland in the 1990s: O26:H11 (four strains), O26:HNM (HNM indicates nonmotile), O2:H29, O91:H21, O91:H40, O101:HNM, O107:H27, O157:HNM, O165:H25, OX3:H21, and Rough:H49. All O157:H7 and O26:H11 isolates produced enterohemolysin, but seven of the other STEC strains did not. Most (n = 63) of the 71 STEC strains isolated carried the stx2 gene only, five carried the stx1 gene only, and three carried both genes. The eaeA gene was detected in all other isolates except five non-O157 strains. There were seven distinct pulsed-field gel electrophoresis (PFGE) genotypes among 57 O157 strains and three distinct PFGE types among four O26:H11 strains. The main PFGE type was found among 65% of all O157 isolates.

Association of enterohemorrhagic Escherichia coli hemolysin with serotypes of shiga-like-toxin-producing Escherichia coli of human and bovine origins

In this study we investigated whether the enterohemorrhagic Escherichia coli (EHEC) hemolysin gene ehxA could be used as an indicator of pathogenicity in Shiga-like-toxin-producing Escherichia coli (SLTEC) isolates. The isolates in a collection of 770 SLTEC strains of human and bovine origins were assigned to group 1 (230 human and 138 bovine SLTEC isolates belonging to serotypes frequently implicated in human disease), group 2 (85 human and 183 bovine isolates belonging to serotypes less frequently implicated in disease), and group 3 (134 bovine isolates belonging to serotypes not implicated in disease). PCR amplification was used to examine all of the SLTEC isolates for the presence of ehxA and the virulence-associated genes eae, slt-I, and slt-II. The percentages of human isolates in groups 1 and 2 that were positive for ehxA were 89 and 46%, respectively, and the percentages of bovine isolates in groups 1 to 3 that were positive for ehxA were 89, 51, and 52%, respectively. The percentages of human isolates in groups 1 and 2 that were positive for eae were 92 and 27%, respectively, and the percentages of bovine isolates in groups 1 to 3 that were positive for eae were 78, 15, and 19%, respectively. The frequencies of both ehxA and eae were significantly higher for group 1 isolates than for group 2 isolates. The presence of the ehxA gene was associated with serotype, as was the presence of the eae gene. Some serotypes, such as O117:H4, lacked both eae and ehxA and have been associated with severe disease, but only infrequently. The slt-I genes were more frequent in group 1 isolates than in group 2 isolates, and the slt-II genes were more frequent in group 2 isolates than in group 1 isolates. In a second experiment we determined the occurrence of the ehxA and slt genes in E. coli isolated from bovine feces. Fecal samples from 175 animals were streaked onto washed sheep erythrocyte agar plates. Eight E. coli-like colonies representing all of the morphological types were transferred to MacConkey agar. A total of 1, 080 E. coli isolates were examined, and the ehxA gene was detected in 12 independent strains, only 3 of which were positive for slt. We concluded that the ehxA gene was less correlated with virulence than the eae gene was and that EHEC hemolysin alone has limited value for screening bovine feces for pathogenic SLTEC because of presence of the ehxA gene in bovine isolates that are not SLTEC.

Isolation and characterization of sorbitol-fermenting Shiga toxin (Verocytotoxin)-producing Escherichia coli O157:H- strains in the Czech Republic

Two sorbitol-fermenting (SF) Shiga toxin-producing Escherichia coli (STEC) O157:H- strains were isolated from patients with hemolytic-uremic syndrome in the Czech Republic in 1995. Their phenotypic and genotypic characteristics and genomic DNA fingerprints were identical or closely related to those of SF STEC O157:H- strains isolated in Germany in 1988 to 1997. This indicates that the Czech isolates belong to the SF STEC O157 clone which is widespread in Germany. It is the first finding of the clone outside Germany.

Detection of hemolysin variants of Shiga toxin-producing Escherichia coli by PCR and culture on vancomycin-cefixime-cefsulodin blood agar

The presence of a hemolysin-encoding gene, elyA or hlyA, from Shiga toxin-producing Escherichia coli (STEC) was detected by PCR in each of 95 strains tested. PCR products of elyA from human STEC isolates of serovars frequently detected in Germany, such as O157:H-, O103:H2, O103:H-, O26:H11, and O26:H-, showed nucleotide sequences identical to previously reported ones for O157:H7 and O111:H- strains. Compared to them, four elyA amplicons derived from human isolates of rare STEC serovars showed identity of about 98% but lacked an AluI restriction site. However, the nucleotide sequence of an amplicon derived from a porcine O138:K81:H- STEC strain was identical to the corresponding region of hlyA, encoding alpha-hemolysin, from E. coli. This hlyA amplicon showed 68% identity with the nucleotide sequence of the corresponding elyA fragment. It differed from the elyA PCR product in restriction fragments generated by AluI, EcoRI, and MluI. Of the 95 representative STEC strains, 88 produced hemolysin on blood agar supplemented with vancomycin (30 mg/liter), cefixime (20 micrograms/liter), and cefsulodin (3 mg/liter) (BVCC). The lowest added numbers of two to six STEC CFU per g of stool or per ml of raw milk were detectable on BVCC plates after seeding of the preenrichment broth, modified tryptic soy broth (mTSB) supplemented with novobiocin (10 mg/liter), with 16 STEC strains. These strains represented the seven prevailing serovars diagnosed from German patients. However, with ground-beef samples, PCR was essential to identify the lowest added numbers of two to six STEC CFU among colonies of hemolyzing Enterobacteriaceae, such as Serratia spp. and alpha-hemolysin-producing E. coli. We conclude that preenrichment of stool and food samples in mTSB for 6 h followed by overnight culturing on BVCC is a simple method for the isolation and presumptive identification of STEC.

Pathogenesis and diagnosis of Shiga toxin-producing Escherichia coli infections

Since their initial recognition 20 years ago, Shiga toxin-producing Escherichia coli (STEC) strains have emerged as an important cause of serious human gastrointestinal disease, which may result in life-threatening complications such as hemolytic-uremic syndrome. Food-borne outbreaks of STEC disease appear to be increasing and, when mass-produced and mass-distributed foods are concerned, can involve large numbers of people. Development of therapeutic and preventative strategies to combat STEC disease requires a thorough understanding of the mechanisms by which STEC organisms colonize the human intestinal tract and cause local and systemic pathological changes. While our knowledge remains incomplete, recent studies have improved our understanding of these processes, particularly the complex interaction between Shiga toxins and host cells, which is central to the pathogenesis of STEC disease. In addition, several putative accessory virulence factors have been identified and partly characterized. The capacity to limit the scale and severity of STEC disease is also dependent upon rapid and sensitive diagnostic procedures for analysis of human samples and suspect vehicles. The increased application of advanced molecular technologies in clinical laboratories has significantly improved our capacity to diagnose STEC infection early in the course of disease and to detect low levels of environmental contamination. This, in turn, has created a potential window of opportunity for future therapeutic intervention.

Studies of Escherichia coli cultured on Rainbow Agar O157 with particular reference to enterohaemorrhagic Escherichia coli (EHEC)

Rainbow Agar O157 is designed for the rapid isolation and identification of enterohaemorrhagic Escherichia coli (EHEC), particularly O157, characterised by black colonies. Five-hundred-eighty-five E. coli strains, including O157, O111 and O113 serogroups from many sources were examined on Rainbow Agar O157. EHEC O157 could readily be isolated and recognized uniquely by typical black colonies. Some other EHEC also stand out as blue-black, whereas O113 and some other EHEC strains were mauve, red or pink and indistinguishable from SLT-negative strains of E. coli.

Evolution of enterohemorrhagic Escherichia coli hemolysin plasmids and the locus for enterocyte effacement in shiga toxin-producing E. coli

This study assessed the diversity of the enterohemorrhagic Escherichia coli (EHEC) hemolysin gene (ehxA) in a variety of Shiga toxin-producing E. coli (STEC) serotypes and the relationship between ehxA types and virulence markers on the locus for enterocyte effacement (LEE). Restriction fragment length polymorphism of the ehxA gene and flanking sequences and of the E. coli attaching and effacing (eae) gene was determined for 79 EHEC hemolysin-positive STEC isolates of 37 serotypes. Two main groups of EHEC hemolysin sequences and associated plasmids, which corresponded to the eae-positive and the eae-negative isolates, were delineated. Comparisons of the ehxA gene sequences of representative isolates of each group showed that this gene and the rest of the EHEC hemolysin operon are highly conserved. Digestion of an ehxA PCR product with the restriction endonuclease TaqI showed a unique restriction pattern for eae-negative isolates and another one for isolates of serotypes O157:H7 and O157:NM. A conserved fragment of 5.6 kb with four potential open reading frames was identified on the EHEC hemolysin plasmid of eae-positive STEC. Phylogenetic analysis of a subset of 27 STEC isolates, one enteropathogenic E. coli isolate, and a K-12 reference isolate showed that eae-positive STEC isolates all belong to a single evolutionary lineage and that the EHEC hemolysin plasmid and the ehxA gene evolved within this lineage without recent horizontal transfer. However, the eae gene and the LEE appear to have been transferred horizontally within this STEC lineage on several occasions. The reasons for the lack of transfer or maintenance of the LEE in other STEC lineages are not clear and require further study.

Haemolysin production by strains of Verocytotoxin-producing Escherichia coli

Twenty-one strains of Verocytotoxin-producing Escherichia coli (VTEC) that hybridized with DNA probe CVD419 were examined for the ability to produce haemolysin. With solid media, all strains produced most haemolysin when grown in blood agar tubes and least when grown on blood agar plates incubated in air. Haemolysin production was increased considerably by incubating blood agar plates in an atmosphere comprising 8% carbon dioxide, 40% hydrogen and 52% nitrogen at 37 degrees C for 16 h, followed by 6 h at 21 degrees C in air. Haemolysin production was also increased when strains were grown on L-agar containing the iron chelator ethylenediamine-di(o-hydroxyphenylacetic acid) prior to subculture on blood agar. Intracellular haemolysin was detected in five out of the 21 strains of E. coli grown on L-agar in the atmosphere described above, but haemolysin was not detected in L-broth culture supernatants. The haemolysins lysed guinea pig, mouse and ferret erythrocytes, but not human, rabbit, rat, turkey or chicken erythrocytes. Also, the addition of calcium ions to culture media was not required for haemolytic activity. It was concluded that haemolysins produced by VTEC appear to be quite distinct from E. coli alpha-haemolysin and resemble a form of beta-haemolysin.

Culture supernatant of Shiga toxin-producing Escherichia coli strains provoke fluid accumulation in rabbit ileal loops

Production of Shiga toxin (Stx) in Escherichia coli strains belonging to serogroups O26, O111, and O157 was evaluated in the rabbit ileal loop assay and results were compared to those using tissue culture assays and DNA hybridization with specific probes for Stx1 and Stx2. All 14 Shiga toxin-producing E. coli strains tested provoked fluid accumulation in the rabbit intestinal loop. Eleven strains hybridized with Stx1 probe, one strain with Stx2 and two strains with both probes. Filtered culture supernatants of all E. coli strains presented cytotoxic effects in both HeLa and Vero cells. In this study, we found a strong association between the production of Stx and its effect in an animal model. This is the first description of high-level Stx-producing E. coli O111ac isolated in Brazil.

Virulence factors of verocytotoxin-producing Escherichia coli isolated from raw meats

PCR for verocytotoxin-producing Escherichia coli (VTEC) was positive in 4.6% of 2,440 raw meat samples; only beef, sheep, and venison samples were positive. None of the isolated VTEC strains belonged to serogroup O157. Additional virulence factors were detected in only a minority of strains, suggesting that most of these meat VTEC isolates are not pathogenic.

Epidemiological relatedness and clonal types of natural populations of Escherichia coli strains producing Shiga toxins in separate populations of cattle and sheep

Two separate animal populations consisting of a herd of cattle (19 animals) and a flock of sheep (25 animals) were investigated for strains of Escherichia coli producing Shiga toxins (STEC) over a time period of 6 months. Thirty-three STEC were isolated from 63.2% of cattle and grouped into 11 serotypes and eight electrophoretic types (ETs) by multilocus enzyme analysis. In sheep, 88% of the animals excreted STEC (n = 67 isolates) belonging to 17 different serotypes and 12 different ETs. STEC from cattle and sheep differed with respect to serotype, and only 4 of the 16 ETs occurred in both animal populations. In cattle, ET14 (O116:H21) strains predominated, whereas other STEC serotypes occurred only sporadically. The predominating STEC types in sheep were ET4 (O125 strains), ET11 (O128:H2 and others), and ET14 (O146:H21). In contrast to their diversity, STEC originating from the same animal population were similar with respect to Shiga toxin (stxy genes. Almost all STEC isolated from cattle were positive for stx2 and stx2c; only one was positive for stx1. In sheep, almost all STEC isolated were positive for stx1 and stx2, whereas stx2c was not found. XbaI-digested DNAs of genetically closely related O146:H21 strains have different restriction profiles which were associated with size alterations in XbaI fragments hybridizing with stx1- and stx2-specific DNA probes. Our results indicate that stx-encoding bacteriophages might be the origin of the genetic heterogeneity in STEC from animals.

Non-O157 Vero cytotoxin producing Escherichia coli: aetiological agents of diarrhoea in children in Dunedin, New Zealand

Strains of Escherichia coli that produce Vero cytotoxin (VTEC) commonly cause diarrhoea, haemorrhagic colitis and haemolytic-uraemic syndrome in many northern hemisphere countries. In these countries, serotype O157:H7/H-predominates and has caused large food-borne outbreaks of infection. In contrast, few cases of infection with this serotype have been reported in New Zealand. Over a 3-month period, 484 stool specimens submitted to medical laboratories in Dunedin were screened for E. coli O157:H7/H-using sorbitol MacConkey agar, Y1 and Vero cell assays. Where possible, Vero cytotoxin production was confirmed by an ELISA test. Specimens from children aged 12 years or less were additionally screened for non-O157 VTEC. In the specimens of the children tested, O157:H7/H-VTEC was not isolated, but VTEC belonging to other serogroups were isolated from the children. Of interest was the detection of other species of Enterobacteriaceae, which produced a cytopathic effect on Vero cells. This study confirms the low incidence of infection with O157:H7/H- VTEC in New Zealand and suggests that non-O157 VTEC is a more important cause of diarrhoeal disease.

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

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

Hemolysin phenotypes and genotypes of eaeA-positive and eaeA-negative bovine verotoxigenic Escherichia coli

Intimin or EaeA protein has been implicated in the attaching/effacing lesion caused by entero-hemorrhagic Escherichia coli (EHEC) in the intestine but it is not produced by all EHEC and is therefore not adequate as a marker for EHEC. Hemolysins are produced by a high percentage of verotoxigenic E. coli (VTEC) and could be a marker for EHEC, but their distribution and relation to virulence are not known. We used PCR amplification to determine the presence or absence of eaeA sequences in 281 VTEC isolates from the feces of healthy cattle. There were 101 eaeA-positive isolates, which belonged to O groups 5, 26, 69, 80, 84, 98, 103, 111, 119, 145, 157 and 108 eaeA-negative isolates, which belonged to O groups 8, 22, 38, 113, 119, 116, 132, 153, 156 or untypable. All isolates were tested for hemolysis on horse blood agar and on washed sheep blood agar. PCR amplification was used to test for EHEC hemolysin, Ehly1, Ehly2 and alpha-hemolysin D sequences. Among eaeA-positive isolates 98% were positive for EHEC hemolysin sequences and were hemolytic on washed sheep red blood cell agar; the corresponding percentage for eaeA-negative isolates was 36%. Ehly1 and Ehly2 sequences were present in only 11 isolates (O groups 26, 84, 119 and 132). None of the eaeA-positive and 13 of the eaeA-negative isolates (including all 11 isolates of O group 132) were positive for alpha-hemolysin D gene sequences by PCR and alpha-hemolysin production on horse blood agar. We conclude that since Ehly1, Ehly2 and alpha-hemolysin occur at low frequency among bovine VTEC and serotypes implicated in human disease they are unlikely to be significant virulence factors. In contrast, EHEC hemolysin was present in almost all eaeA-positive VTEC isolates and in approximately one-third the eaeA-negative ones; it may be both a virulence marker and virulence factor but further testing is required. The study identified isolates with all combinations of eaeA and EHEC hly, which may be useful for further testing.

Rapid detection and isolation of shiga-like toxin (verocytotoxin)-producing Escherichia coli by direct testing of individual enterohemolytic colonies from washed sheep blood agar plates in the VTEC-RPLA assay

By combining the enterohemolysin test and the VTEC-RPLA test (specific for the detection of Shiga-like toxin I [SLT-I], SLT-II, and SLT-IIc), single colonies of SLT-producing Escherichia coli were found to constitute between 0.03 and 68.1% of the coliform flora in human stool cultures and were isolated and characterized within 72 to 96 h.

Enterohemolytic phenotypes and genotypes of shiga toxin-producing Escherichia coli O111 strains from patients with diarrhea and hemolytic-uremic syndrome

Thirty-six Shiga toxin-producing Escherichia coli (STEC) O111:H- strains, 18 of which were isolated from patients with hemolytic-uremic syndrome (HUS) and 18 from patients suffering from diarrhea, were investigated for their enterohemolytic phenotypes and genotypes. Twenty-two strains were EHEC hemolysin (EHEC Hly) positive by probe hybridization and by PCR with sequences complementary to the EHEC hlyA gene of E. coli O157:H7, but only 20 of these were hemolytic on blood agar plates. The remaining 14 strains were EHEC Hly negative according to DNA-based methods and did not express the enterohemolytic phenotype. The enterohemolytic phenotype was observed in 16 of 18 (88%) strains from patients with HUS but only in 4 of 18 (22.2%) of the STEC O111:H- strains from patients with diarrhea. All STEC O111:H- strains carried large plasmids, as shown by plasmid analysis, but only plasmids of EHEC Hly probe-positive strains hybridized with the CVD419 probe. A BamHI fragment of approximately 12 kb was cloned from the large plasmid of the E. coli O111:H- strain 78/92 and shown to mediate hemolytic activity when transformed into the E. coli laboratory strain HB101. The EHEC O111 hlyA gene was sequenced completely and shown to have 99.4% sequence identity to the corresponding EHEC O157 hlyA gene of the E. coli O157:H7 strain EDL 933. Our results indicate that detection of EHEC Hly either by DNA-based methods or by investigation of the enterohemolytic phenotype on blood agar alone is insufficient for screening STEC O111 strains. However, the high incidence of EHEC Hly in isolates from patients with HUS and its rare occurrence in isolates from patients with diarrhea may indicate that STEC O111 strains have a distinct pathogenic potential for humans and that the presence of EHEC Hly increases the ability of an STEC O111 strain to cause extraintestinal complications in humans.

Escherichia coli and virus isolated from "sticky kits"

A total of 121 Escherichia coli strains isolated from 3-week-old mink kits were serotyped and examined for virulence factors. 56 strains were isolated from healthy kits while 65 were from "sticky kits". Among these, 34 different serotypes were detected. No difference in serotypes or the presence of virulence factors could be detected between healthy and diseased kits. By electron microscopy of faecal samples corona-, rota-, and calicivirus were demonstrated among healthy as well as diseased kits.

The enterohemolysin phenotype of bovine Shiga-like toxin-producing Escherichia coli (SLTEC) is encoded by the EHEC-hemolysin gene

Naturally occurring enterohemolysin negative variants were observed during studies on bovine Shiga-like toxin-producing E. coli (SLTEC). Examination of three strains (413/89-1 and 332, 026:H-, and 570/89, O111:H-) and their isogenic variants (413/89-6, 332-I and 570/89-I, respectively) showed, that in each strain loss of the enterohemolytic phenotype correlated with the loss of a large plasmid ranging from 94 to 104 kb in size. The hemolysin determinant present on the 94 kb plasmid of strain 413/89-1 was cloned and discovered by DNA and N-terminal aminoacid sequence analysis to be highly homologous to the recently published EHEC-hemolysin (HlyEHEC; Schmidt et al., 1994; 1995). When a recombinant plasmid harboring this determinant was reintroduced into the enterohemolysin negative isogenic mutant 413/89-6, the enterohemolytic phenotype was restored. Southern blot hybridization analysis was used to demonstrate that the HlyEHEC is plasmid-borne in SLTEC-strains. Our cumulative data suggest that the enterohemolytic phenotype of SLTEC is encoded by the plasmid-borne HlyEHEC. These results further demonstrate the close similarity between SLTEC-isolates from bovine and human.

Characterization of Escherichia coli isolated from foals

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

Enterohaemorrhagic Escherichia coli: a new problem, an old group of organisms

All mammals are colonised by Escherichia coli generally at birth and these organisms become part of their intestinal flora for the rest of their lives. New types are acquired generally by an oral route. Some E coli are pathogenic and some may have a far more enhanced ability to colonise the human intestine than most others. Recently enterohaemorrhagic E coli have emerged. They can cause a number of intestinal illnesses in humans including bloody diarrhoea and haemolytic uraemic syndrome. These organisms produce a number of virulence factors particularly the Shiga-like toxins (verotoxins). The intestines of animals may be the reservoir of these organisms for human infection, and cattle particularly have been shown to harbour them. Food, especially undercooked meat products, have been associated with a number of outbreaks throughout the world. While a certain serotype O157.H7 has been associated with many outbreaks throughout the world, other serotypes, particularly O111.H-, have also been reported. This latter serotype appears to be more common in Australia.

Escherichia coli and virus isolated from "sticky kits"

A total of 121 Escherichia coli strains isolated from 3-week-old mink kits were serotyped and examined for virulence factors. 56 strains were isolated from healthy kits while 65 were from "sticky kits". Among these, 34 different serotypes were detected. No difference in serotypes or the presence of virulence factors could be detected between healthy and diseased kits. By electron microscopy of faecal samples corona-, rota-, and calicivirus were demonstrated among healthy as well as diseased kits.

Clonal relatedness of Shiga-like toxin-producing Escherichia coli O101 strains of human and porcine origin

Shiga-like toxin (SLT)-producing Escherichia coli (SLTEC) O101 has recently been associated with hemorrhagic colitis and hemolytic-uremic syndrome in humans. In this study, SLTEC O101 strains from humans and pigs were characterized for clonal relatedness by nucleotide sequence analysis of their slt genes, DNA finger-printing of genomic DNA, and determination of virulence factors. The slt genes of five E. coli O101 strains were cloned and sequenced. For all strains, the deduced amino acid sequences of the B subunits were identical to those of the SLT-IIe present in the classical SLTEC O139 strains that cause edema disease in pigs. The A subunit revealed more than 99% homology to that of SLT-IIe. DNA fingerprinting revealed a high degree of genetic relatedness between the human and porcine O101 isolates. None of the O101 strains investigated had virulence factors frequently found in porcine (F107 fimbriae or heat-stable or heat-labile enterotoxins) or human SLTEC strains (eaeA or enterohemorrhagic E. coli hemolysin). The absence of virulence factors typical of SLT-I- and SLT-II-producing E. Coli together with the presence of SLT-IIe, a toxin previously seen only in porcine E. coli, suggests a new pathogenic mechanism for E. coli O101 infection of humans. For diagnostic purposes, we recommend the use of PCR primers and DNA probes complementary to slt-IIe to correctly identify such strains and to further evaluate their role in human diseases.

Association between alpha-hemolysin production and HeLa cell-detaching activity in fecal isolates of Escherichia coli

Escherichia coli isolates that cause detachment of cell monolayers during in vitro adherence assays (cell-detaching E. coli [CDEC]) were recently reported as a potential new group of enteropathogenic bacteria. In the present study, 269 E. coli isolates from feces of children 1 to 5 years of age were identified as CDEC in a detaching assay developed with HeLa cells. The great majority of these isolates were hemolytic within 3 h of growth on blood agar plates and hybridized with a DNA probe for alpha-hemolysin (93.7%), while most of the non-detaching isolates were hemolytic within 24 h (3.6%) or nonhemolytic (94.8%). E. coli isolates that produced alpha-hemolysin were found in 60 (30%) of 200 children with diarrhea and 47 (24%) of 200 age-matched controls. No statistical significance was found for the differences in alpha-hemolysin production among the matched pairs (P = 0.2). These data suggest that CDEC isolates are not associated with diarrhea in the population studied.