Expression of verocytotoxic Escherichia coli antigens in tobacco seeds and evaluation of gut immunity after oral administration in mouse model

Verocytotoxic Escherichia (E.) coli strains are responsible for swine oedema disease, which is an enterotoxaemia that causes economic losses in the pig industry. The production of a vaccine for oral administration in transgenic seeds could be an efficient system to stimulate local immunity. This study was conducted to transform tobacco plants for the seed-specific expression of antigenic proteins from a porcine verocytotoxic E. coli strain. Parameters related to an immunological response and possible adverse effects on the oral administration of obtained tobacco seeds were evaluated in a mouse model. Tobacco was transformed via Agrobacteium tumefaciens with chimeric constructs containing structural parts of the major subunit FedA of the F18 adhesive fimbriae and VT2e B-subunit genes under control of a seed specific GLOB promoter. We showed that the foreign Vt2e-B and F18 genes were stably accumulated in storage tissue by the immunostaining method. In addition, Balb-C mice receiving transgenic tobacco seeds via the oral route showed a significant increase in IgA-positive plasma cell presence in tunica propria when compared to the control group with no observed adverse effects. Our findings encourage future studies focusing on swine for evaluation of the protective effects of transformed tobacco seeds against E. coli infection.

[Genotypic characterization of toxigenic Escherichia coli isolated from pigs with postweaning diarrhea (PWD) and edema disease (ED)]

The purpose of this work was to characterize 47 Escherichia coli strains isolated from 32 pigs diagnosed with postweaning diarrhea and three pigs with edema disease by PCR. Forty two (95.5 %) of the strains isolated from diarrheic pigs were characterized as enterotoxigenic E. coli (ETEC) and 2 (4.5 %) as Shiga toxin-producing E. coli (STEC). Fourteen (33.3 %) ETEC strains were positive for est/estII/fedA genes. The most complex genotype was eltA/estI/faeG/aidA. Strains isolated from pigs with ED were classified as porcine STEC and were stx2e/aidA carriers. Eleven (25 %) strains carried the gene encoding adhesin protein AIDA-I. However, genes coding for F5, F6, F41, intimin and Paa were not detected. The development of vaccines generating antibodies against prevalent E. coli adhesins in Argentina could be useful for the prevention of PWD and ED.

Phenotyping of E. coli serotypes associated to oedema disease

BACKGROUND

Oedema disease is a severe disease, mainly affecting recently weaned pigs. It is caused by E. coli strains that express fimbriae F18 and produce verotoxin 2e, mainly belonging to serotype O138, O139 or O141. The aim of this study was to compare E. coli isolates within these serotypes with respect to diversity.

METHODS

Faecal E. coli strains belonging to serotypes O138, O139 and O141 isolated during the period 1994-1998 from Swedish pigs aged less than 12 weeks were compared using a biochemical fingerprinting system. Aiming to compare the results obtained over time, also strains isolated during 1964-67 and 1975-80 were included in the study. The study comprised 129, 263 and 95 isolates of E. coli serotype O138, O139 and O141, respectively.

RESULTS

Biochemical phenotypes (BPTs) were defined. At each sampling occasion each herd could only contribute with one isolate per BPT. Consequently, all but one of identical BPTs identified at a specific sampling occasion was omitted. The final number of isolates from 1994-98 that was compared included 64, 182 and 41 isolates of serotypes O138, O139 and O141, respectively. Within each serotype, the dominating BPT included over 65% of the compared isolates, demonstrating a large dominance of one BPT per serotype. These dominating BPTs were also demonstrated in the material from the 1960ies and the 1970ies. Still, the presence of other common BPTs (especially within serotype O138 and O139) demonstrated a certain variation within serotype. In a herd severely affected by oedema disease, E. coli serotype O139 was easily demonstrated in diseased pigs but only rarely in apparently healthy weaners

CONCLUSION

The results obtained demonstrate the presence of dominating BPTs within the oedema disease inducing serotypes. A stability of these BPTs over time was observed, presumably at least partly due to a never-ending access to naïve pigs. Still, the presence of other common BPTs indicates a variation over time, which visualises the importance of monitoring for this. Such studies should focus on pigs affected by oedema disease, because oedema disease inducing strains of E. coli were only rarely demonstrated in healthy pigs in a herd affected by oedema disease.

Molecular characterization of shiga like toxin-producing Escherichia coli (STEC) isolates from pigs oedema

BACKGROUND & OBJECTIVE

An oedema outbreak occurred in a Guwahati pig farm. Escherichia coli isolates from different necropsy samples collected from the dead piglets with oedema were characterized to confirm the virulence.

METHODS

Haemolytic E. coli isolates recovered from liver, lung and intestine of pigs with oedema were examined for presence of genes encoding pathogroups such as enteropathogenic Escherichia coli (EPEC), (eae/bfpA), enteroaggregative Escherichia coli (EAggEC), (eagg), enterotoxigive Escherichia coil (ETEC), (elt/est) and shiga like toxin producing Escherichia coli (STEC), (stx1/ stx2) by PCR and molecular typing by randomly amplified polymorphic DNA-PCR (RAPD-PCR).

RESULTS

The three haemolytic E. coli recovered from diseased pigs were STEC because of presence of the stx2 and eae genes. Analysis by RAPD-PCR indicated that two of the three isolates were genetically related.

INTERPRETATION & CONCLUSION

The isolation of STEC isolates from pigs with oedema was shown. Although the three isolates were untypable, presence of eae and stx2 genes clearly indicated these as prime cause of pig oedema disease. Further, demonstration of STEC in pigs becomes a public health concern, as pigs are potential reservoir of such agents, which may cause human illness.

The effect of intramuscular administration of colistin on the development and course of experimentally induced oedema disease in weaned piglets

Shiga-toxigenic E. coli (STEC) strains that produce Shiga toxin Stx2e cause oedema disease in weaned piglets. The purpose of the present study was to investigate the impact of Stx2e released in mesenteric lymph nodes on disease pathogenesis. Colistin and ampicillin were intramuscularly administered to piglets of the experimental group simultaneously challenged with STEC strain, type O139:F18ab, Stx2e+. Piglets of the control group were challenged with STEC only. The strain was naturally resistant to ampicillin and susceptible to colistin. After the challenge, colonisation of the intestines was observed in both antibiotic-treated piglets and control piglets without antibiotic treatment. Histochemistry and scanning electron microscopy revealed sporadic colonisation of the small intestine in the piglets. STEC was detected in the mesenteric lymph nodes of untreated piglets. The clinical manifestations of oedema disease were observed in both groups. In the antibiotic-treated group (11 piglets), oedema disease developed in 10 piglets, eight of which died or were euthanized ante finem. In the untreated group (11 piglets), oedema disease developed in five piglets, four of which died or were euthanized ante finem. We therefore propose that the STEC lysed by colistin suddenly released the toxin from bacterial cells immediately after their passage through the intestinal wall. That could explain a more severe course of oedema disease in the treated piglets. Even though high amounts of STEC were present in the lymph nodes of untreated piglets, the toxin was not released abruptly because the bacterial cells were not damaged.

[Expression of GST-3B fusion protein of Escherichia coli of Ee strain producing SLT-IIe toxin and study on its biological activities and immunogenicity]

Three copies of DNA fragment encoding the truncated SLT-IIeB of Ee strain which was responsible for the edema disease in piglets in Hubei province were fused to the downstream of glutathione S-transferase (GST) of pGEX-KG expression vector, resulting in the fusion expression plasmid pK3 B. After transformed into E. coli BL21 (DE3) and induced by IPTG, the results of SDS-PAGE showed that the GST-3B fusion protein was expressed in high level. Western blot was performed to confirm that the expressed fusion protein could specifically react with antiserum against diseases of edema of swine. The fusion protein was further purified and used as an antigen for receptor-binding inhibition assay. The receptor-binding inhibition assay showed GST-3B fusion protein had more strong biological activities than GST-B. The fusion protein of GST-3B or GST-B was purified and emulsified with Freund' s incomplete adjuvant in equal volumes to get subunit bacterin. Groups of SPF KM mice were vaccinated subcutaneously at 0 week with 25 micrograms and at 2 weeks with 25 micrograms of purified GST-3B or GST-B and challenged intraperitoneally with volume of 5 x OD50 Ee strain. Serological tests were performed one week interval with ELISA. The IgG titres against SLT-IIeB in the sera collected at the same period from the Group GST-3B were higher than in the Group GST-B and the immune protection rate against Ee strain was respectively 60% and 40%. These results show the fusion protein GST-3B had more strong biological activities, immunogenicity and better protection against Ee strain, which built a good foundation for the further research of high efficacy vaccine against porcine edema disease.

Virulence and fitness gene patterns of Shiga toxin-encoding Escherichia coli isolated from pigs with edema disease or diarrhea in Germany

Fecal Escherichia coli isolates (n = 3,218) from piglets with edema disease or diarrhea were screened for the genes of Stx2 and Stx2 variants. A total of 283 E. coli isolates (8.8%) proved exclusively positive for Stx2e and most of these (85.1%) harbored genes for F18 fimbria. No recognized adhesins were detectable in 14.5% of the isolates. Genes for heat-stable or heat-labile E. coli enterotoxins were found in F18+ as well as F18 isolates (51.9% and 33.3%, respectively). Five isolates also harbored fyuA and irp2 genes which are indicative of a high pathogenicity island in E. coli. All Stx2e+ isolates lacked genes for intimin, EHEC hemolysin, STEC autoagglutinating adhesin, subtilase cytotoxin, serine protease Espl. The majority of Stx2e+ isolates belonged to phylogenetic groups A (59.3%) and D (38.9%) and only few isolates were classified as B1 and B2 (1.8%). The results suggest that Stx2e-producing E. coli strains are highly prevalent in diseased pigs in Germany. Despite their significant diversity, most strains possess all typical features (Stx2e, F18) of porcine edema disease E. coli. However, a considerable portion of porcine strains resembles published human Stx2e+ strains in that they lack any recognized pig-associated adhesin. Thus, a zoonotic potential cannot be excluded for these strains.

The age-dependent expression of the F18+ E. coli receptor on porcine gut epithelial cells is positively correlated with the presence of histo-blood group antigens

F18(+)Escherichia coli have the ability to colonize the gut and cause oedema disease or post-weaning diarrhoea by adhering to specific F18 receptors (F18R) on the porcine epithelium. Although it is well established that a DNA polymorphism on base pair 307 of the FUT1 gene, encoding an alpha(1,2)fucosyltransferase, accounts for the F18R phenotype, the F18R nature is not elucidated yet. The aim of the present study was to investigate the correlation between the presence of H-2 histo-blood group antigens (HBGAs) or its derivative A-2 HBGAs on the porcine gut epithelium and F18(+)E. coli adherence. A significant positive correlation was found between expression of both the H-2 (r=0.586, P<0.01) and A-2 (r=0.775, P<0.01) HBGAs and F18(+)E. coli adherence after examination of 74 pigs aged from 0 to 23 weeks. The majority of the genetically resistant pigs (FUT1M307(A/A)) showed no HBGA expression (91.7%) and no F18(+)E. coli adherence (83.3%). In addition, it was found that F18R expression levels rise with increasing age during the first 3 weeks after birth and that F18R expression is maintained in older pigs (3-23 weeks old). Taken together, these data suggest that, apart from H-2 HBGAs, A-2 HBGAs might be involved in F18(+)E. coli adherence.

A study of edema disease in pigs in Vietnam with particular reference to the use of autovaccine for the prevention of disease

Edema disease caused by Escherichia coli is one of the most common diseases in postweaning piglets throughout Vietnam. Verotoxigenic E. coli (VTEC) was isolated from 197 of 261 samples (75.5%). All isolates were confirmed by basic biochemical tests and carbohydrate fermentation characteristics. Of these, 70.1% of isolates are hemolytic, 45% isolates belonged to serotypes O149:K91, possessed the VT2e gene, and was the most predominant VTEC pathotype associated with edema disease in pigs. Serogroup O139 accounted for 30% of the isolates, followed by serogroup O138 and O141 (25%). In addition to VT2e gene, the ST (72.7%) and LT (52.7%) genes were also recognized. A total of 10 representative isolates were subjected to toxigenicity testing by intraperitoneal injection in mice and experimental infection in pigs. It was shown that 100% of the mice were killed 17-24 h post injection (p.i.). All pigs experimentally infected with challenge strains and developed typical symptoms of edema disease 36-72 h p.i. A multivalent killed whole-cells vaccine containing aluminum hydroxide was prepared from 5 VTEC strains. The vaccine was 100% safe when administered by the intramuscular route into the pigs. A field trial for over 100,000 pigs (21-90 days old) showed that vaccinated pigs were protected against edema disease at a level of 90% compared to 100% of pigs from unvaccinated groups.

DNA microarray-based identification of serogroups and virulence gene patterns of Escherichia coli isolates associated with porcine postweaning diarrhea and edema disease

Escherichia coli strains causing postweaning diarrhea (PWD) and edema disease (ED) in pigs are limited to a number of serogroups, with O8, O45, O138, O139, O141, O147, O149, and O157 being the most commonly reported worldwide. In this study, a DNA microarray based on the O-antigen-specific genes of all 8 E. coli serogroups, as well as 11 genes encoding adhesion factors and exotoxins associated with PWD and ED, was developed for the identification of related serogroups and virulence gene patterns. The microarray method was tested against 186 E. coli and Shigella O-serogroup reference strains, 13 E. coli reference strains for virulence markers, 43 E. coli clinical isolates, and 12 strains of other bacterial species and shown to be highly specific with reproducible results. The detection sensitivity was 0.1 ng of genomic DNA or 10(3) CFU per 0.3 g of porcine feces in mock samples. Seventeen porcine feces samples from local hoggeries were examined using the microarray, and the result for one sample was verified by the conventional serotyping methods. This microarray can be readily used to screen for the presence of PWD- and ED-associated E. coli in porcine feces samples.

Evaluation of the low dose level of a heat-killed and dried cell preparation of Enterococcus faecalis to prevent porcine edema disease using experimental infection model with enterotoxcemic Escherichia coli in weaning pigs

Porcine edema disease (ED) is caused by Shiga toxin 2e-producing Escherichia coli (STEC). ED has become frequent in pig farms, and the use of antimicrobials has resulted in the development of antimicrobial-resistant STEC. Accordingly, the use of materials other than antimicrobials is requested for the prevention of ED. Oral administration of a heat-killed and dried cell preparation of Enterococcus faecalis strain EC-12 (EC-12) to weaning pigs was previously demonstrated to decrease animal mortality in a STEC-contaminated farm at 0.05% (w/w) dose level. In this study, pigs experimentally infected with STEC were used as a model for ED to evaluate the low dose level of EC-12 to prevent ED. Fifteen 21-day-old pigs were divided into 5 groups: STEC challenge with the basal diet, STEC challenge with EC-12 supplemented at 0.005, 0.01, or 0.05% (w/w) to the basal diet, and no STEC challenge with the basal diet. The challenge was carried out when the animals were 25, 26, and 27 days old using STEC contained in capsules resistant against gastric digestion. All pigs were euthanized at 32 days of age. The daily weight gain, feed conversion ratio, and palpebral edema were improved by supplementation with 0.05% EC-12, but not by the low dose levels. Accordingly, 0.05% level of supplementation was needed for EC-12 to improve clinical symptoms in weaning piglets infected by STEC.

Monoclonal antibodies reveal a weak interaction between the F18 fimbrial adhesin FedF and the major subunit FedA

F18+ Escherichia coli can cause post-weaning diarrhoea and oedema disease in pigs. These diseases are responsible for substantial economic losses, but a vaccine is not available. A good knowledge of the characteristic of the fimbriae is useful for the development of a vaccine composed of the fimbrial virulence factor. F18 fimbriae are composed of the major subunit FedA and the minor subunits FedE and the adhesin FedF. In the present study monoclonal antibodies (mAbs) against FedA and FedF were produced. In addition to their diagnostic value, these mAbs revealed a weaker interaction between FedA and FedF compared to the subunit-subunit interactions in other fimbriae, like type 1 and P pili. Further experiments are needed to investigate if this weak interaction could be one of the reasons for the slow colonisation of the small intestinal mucosa by F18+ E. coli.

Edema disease caused by a clone of Escherichia coli O147

Edema disease is a systemic disease of weaned pigs caused by host-adapted strains of Escherichia coli, most commonly belonging to serogroup O138, O139, or O141. In the late 1990s, E. coli O147 strains containing the virulence genes f18, sta, stb, and stx(2) were recovered from outbreaks of edema disease in the United States. Pulsed-field gel electrophoresis (PFGE) was used to determine that the majority of these strains (34/43) were closely related to one another. Subsequent analysis by multilocus restriction typing confirmed the PFGE results and indicated that the cluster of edema disease strains were only distantly related to other E. coli O147 strains. Serogrouping of edema disease isolates from the Iowa State University Veterinary Diagnostic laboratory recovered between 1996 and 2000 indicated that 42% belonged to serogroup O147. Our data suggest that these strains may be a common serotype of edema disease-causing E. coli in the United States.

Experimental infection of enterotoxemic Escherichia coli associated with porcine edema disease and its pathologic characteristics in the intestine

Edema disease (ED) has become frequent in Japan, but no effective method for experimental infection has been developed. We report here the use of a capsule that resistant against gastric digestion to induce the ED in piglets. Four 21-day-old piglets were used. Shiga toxin 2e-producing Escherichia coli (STEC) cell pellet was encapsulated and administered orally. Two pigs received 1.0x10(10) CFU for two days, and the others received 3.9x10(8) CFU for three days. The high-dose group caused the typical clinical ED signs (palpebral edema or neurologic impairment). Eosinophil infiltration, swollen lymphoid follicles, and edema were observed in the ileum. The kidney had the thrombus in the glomerulus.

PCR detection of virulence factor genes in Escherichia coli isolates from weaned piglets with edema disease and/or diarrhea in China

Fimbriae, toxins and pathogenicity islands (PAIs) are main virulence factors of the pathogenic Escherichia coli strains. To investigate into their prevalence in clinical E. coli isolates associated with porcine postweaning diarrhea (PWD) and/or pig edema disease (ED), 240 isolates were obtained from diseased piglets (140 from PWD, 76 from ED and 24 from ED/PWD) and submitted to PCR detection for genes coding for fimbriae, enterotoxins, shiga toxins, intimin and high-molecular-weight protein 2 (HMWP2). Among the 240 isolates detected, detection rates of the genes for F18, F4, intimin, HMWP2, Stx2e, LTa, STa and STb were 26.25%, 3.75%, 28.33%, 16.67%, 35%, 10.83%, 14.58% and 9.17%, respectively, and 67.92% of the isolates could be assigned into 20 different virulence factor patterns. Further more, F18ab+ STEC are the prevalent pathogens of ED, and F18+ and/or intimin+ STEC/ETEC are the dominant pathogens of ED/PWD, while F18ab+, F4+ and/or intimin+ ETEC and HPI+ and/or LEE+ E. coli are more frequently associated with PWD.

Prevalence of fimbial colonization factors F18ab and F18ac in Escherichia coli isolates from weaned piglets with edema and/or diarrhea in China

F18ab and F18ac are important fimbrial colonization factors of verotoxigenic Escherichia coli (VTEC) and/or enterotoxigenic E. coli (ETEC) in weaned piglets with edema disease and/or diarrhea. To further investigate their prevalence and correlation to pathogenic E. coli, a duplex PCR, using three primers derived from the nucleotide sequence of the F18 major fimbrial subunit gene (fedA), and a direct agglutination test, using a monoclonal antibody specific for the antigenic factor 'a' of F18, were performed. Among 60VTEC, 24VTEC/ETEC and 24 ETEC isolates tested from weaned piglets with edema disease and/or diarrhea in different pig farms in the Jiangsu Province of China, 52 isolates (48.15%) were positive in the direct agglutination test and 63 isolates (58.33%) were positive in the duplex PCR. Among 63 PCR-positive isolates, 53 isolates (49.07%) were F18ab-positive and 10 isolates (9.26%) were F18ac-positive. In addition, the F18ab gene was more frequently detected in VTEC (61.67%) or VTEC/ETEC (62.50%) than in ETEC (4.17% only), while the F18ac gene was more frequently detected in VTEC/ETEC (33.33%) than in ETEC (8.33%) or VTEC (0%). Furthermore, F18ab was more frequently associated with Shiga toxin 2e (Stx2e), whereas F18ac was more frequently associated with enterotoxin ST I. These results suggest that the duplex PCR performed in this experiment is a more reliable method for identification of F18+E. coli, and that F18 is a more important virulence factor of VTEC and VTEC/ETEC.

Inhibitory activities of colicins against Escherichia coli strains responsible for postweaning diarrhea and edema disease in swine

The efficacies of colicins E1 and N against Escherichia coli strains responsible for postweaning diarrhea and edema disease, two of the most prevalent disease problems for pigs in the United States, were determined in vitro. These proteins may provide an environmentally sound means for the prevention of these infections in swine.

Prevalence and deletion types of the pathogenicity island ETT2 among Escherichia coli strains from oedema disease and colibacillosis in pigs

Piglet pathogenic Escherichia coli encoding Shigatoxin 2e and F18 adhesins are the etiological agents of oedema disease as well as of non-oedema disease colibacillosis. In order to reveal virulence differences among this pathogen, the presence of the pathogenicity island (PAI) E. coli type three secretion system 2 (ETT2) was examined. Using PCR and Southern blot techniques for the identification of the right, the middle, and the left region of this 29.9kb large genetic element, the entire ETT2 was found among E. coli O138:H(-), O139:H1, and O147:H6 strains originated from cases of oedema disease in Germany between 1995 and 2001 and belonging to various clonal types. In contrast, non-oedema disease E. coli isolates (e.g. O8:H19, 101:H(-), O141:H4) contain deleted subtypes of ETT2. These deletions cover the translocon part of the putative ETT2-encoded type III secretion apparatus. It is suggested that the entire ETT2 is associated with a particular virulence trait of piglet oedema disease E. coli (EDEC).

Effect of Antimicrobial Agents on the Production and Release of Shiga Toxin by Enterotoxaemic Escherichia coli Isolates from Pigs

Edema disease (ED) of pigs is an enterotoxaemic disease caused by enterotoxaemic Escherichia coli (ETEEC) infection. Antimicrobial therapy for pigs with ED is controversial because it may induce death of sickish piglets. In this study, we investigated the effects in vitro of 7 antimicrobial agents, ampicillin, gentamicin, colistin, bicozamycin, fosfomycin, sulfamethoxazole-trimethoprim and enrofloxacin, on the release and production of shiga toxin (Stx) 2e by ETEEC strains. We found that more Stx 2e accumulated in the bacterial cells than was released into supernatant. Associated with inhibition of cell wall synthesis, the exposure to ampicillin or fosfomycin increased the release of Stx 2e. The production levels of Stx 2e in all antimicrobial-treated cultures were equal to the level in the control or less than in the control. These results suggest that cell wall synthesis inhibitors, such as ampicillin and fosfomycin, may change for the worse in the signs in ETEEC infectious pigs. On the other hand, gentamicin, colistin, bicozamycin and enrofloxacin may be useful for the treatment of pigs with ED.

Antimicrobial susceptibilities of Shiga toxin-producing Escherichia coli isolates from pigs with edema disease in Japan

Fifty-seven Shiga toxin-producing Escherichia coli (STEC) strains isolated from pigs with edema disease (ED) from 1997 to 2001 in Japan were examined for antimicrobial susceptibilities. The susceptibilities were compared with those of E. coli ATCC 23546 isolated from pig with ED in the 1950's. Consequently, the isolated STECs showed high susceptibility to peptides and bicozamycin in a way similar to the reference strain. On the other hand, the STECs showed low susceptibility to beta-lactams, tetracyclines, novobiocin, fosfomycin, trimethoprim, and old quinolones. It became clear that the susceptibilities of the isolated STECs had diminished in regard to antimicrobials.

Characteristics of capsules in enterotoxemic Escherichia coli O139:K12 strains causing swine edema disease

The characteristics of the capsule of the enterotoxemic Escherichia coli (ETEEC) O139:K12 strains that strongly adhere to Hep-2 cells were examined. Electron microscopic studies using the freeze-substitution technique revealed that ETEEC strains had a capsule of approximately 25 nm. These strains show hydrophobic surface properties and strong adherence to human polymorphonuclear leukocytes (PMNs). In contrast, ETEEC strains RK-O139 and ED-1 show weak adherence to HEp-2 cells and fail to express the capsule layer on the cell surface. These ETEEC strains possess hydrophilic surface properties and also adhere to PMNs. The lipopolysaccharide (LPS) analysis by means of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that ETEEC strains had the same LPS profile and long O-side chains of LPS. Furthermore, all strains were resistant to serum killing activity. These results suggest that the capsule of ETEEC strains does not contribute as an antiphagocytic factor, but as an adherence factor to host cells.

Replicon typing of F18 fimbriae encoding plasmids of enterotoxigenic and verotoxigenic Escherichia coli strains from porcine postweaning diarrhoea and oedema disease

The presence of fimbrial adhesin F18 is frequently found in enterotoxigenic Escherichia coli (ETEC) and verotoxigenic E. coli (VTEC) strains responsible for diarrhoea and oedema disease of weaned pigs. The F18 adhesin occurs in two antigenic variants: F18ab is characteristic of VTEC while F18ac is more typical for ETEC. F18 encoding plasmids of 17 phenotypically characterized porcine E. coli isolates (10 ETEC, 6 VTEC and 1 ETEC/VTEC) were tested with a DNA probe for F18 fimbrial adhesin and with replicon probes for the RepFIa, RepFIb and for the RepFIc family of basic replicons. In all the cases, the F18 probe hybridized to only one plasmid band of size higher than 42MDa. All F18 plasmids were determined to be unireplicon plasmids belonging to the RepFIc replicon family of the F incompatibility complex. There was no difference between F18ac plasmids of ETEC and F18ab plasmids of VTEC strains in terms of replicon type or subtype. However, the size of F18ab plasmids of the VTEC strains varied between 42 and 98MDa, in contrast to F18ac plasmids of ETEC strains (constantly approximately 98MDa).

Prevalence of serogroups and virulence genes in Escherichia coli associated with postweaning diarrhoea and edema disease in pigs and a comparison of diagnostic approaches

Identification of Escherichia coli causing porcine postweaning diarrhoea (PWD) or edema disease (ED) requires knowledge regarding the prevalent pathotypes within a given region. This study was undertaken to determine the present distribution of serogroups, hemolytic activity and virulence factor gene profiles among porcine pathogenic E. coli isolates in Denmark and to compare detection of these characteristics as diagnostic approaches. Five hundred and sixty-three E. coli were serogrouped using E. coli O-antisera and investigated for hemolytic activity. Of these, 219 isolates were further characterized using a 5'-nuclease PCR assay detecting genes for adhesion factors, enterotoxins and verocytotoxin 2e (VT2e). Forty-two different serogroups were found. The most prevalent serogroup was O149 accounting for 49.9% of all isolates, followed by O138 (14.9%), O139 (6.9%), O141 (4.1%) and O8 (3.7%). Hemolytic activity was detected in 87.7% of all isolates. Virulence factor genes detected were F4 (44.7%), F18 (39.3%), intimin (1.4%), F6 (0.9%), STb (77.6%), EAST1 (65.8%), LT (61.6%), STa (26.5%) and VT2e (16.4%). Six pathotypes accounted for 65.7% of all isolates investigated. Using possession of virulence factor genes as reference, O-serogrouping employing a selection of antisera representing common pig pathogenic serogroups and detection of hemolysis were evaluated as epidemiological markers for pathogenicity. Both criteria were associated with pathogenicity (P<0.001, for both), however, both methods also resulted in false classifications regarding pathogenicity for 11.9 and 13.2% of isolates, respectively. Detection of adhesion factor genes F4, F18 and intimin is suggested as an operational alternative when diagnosing PWD and ED.

Antimicrobial susceptibility of pathogenic Escherichia coli isolated from pigs in Korea

The in vitro susceptibilities of 285 isolates of Escherichia coli from preweaned and postweaned pigs with diarrhea and edema disease were tested with the 15 commonly used antimicrobial drugs by an agar dilution minimal inhibitory concentration procedure according to National Committee for Clinical Laboratory Standards (NCCLS) guidelines. All E. coli isolates tested in this study belonged to enterotoxigenic E. coli, attaching and effacing E. coli, or Shiga toxin-producing E. coli. Field isolates had low MIC90 for ceftiofur (1 microg/ml). No correlation in antimicrobial resistance was found in three types of E. coli.

Binding of E. coli isolates from pigs with postweaning diarrhea or edema disease to crude intestinal mucin of a weaned pig

The presence of the fedA (gene coding F18 fimbriae) and genes coding STa and LTI enterotoxins and verotoxin Stx2v was determined in 30 E. coli strains isolated from weaned pigs with postweaning diarrhea (PWD) and edema disease (ED). The fedA gene was detected in 22 strains (73.3%). It was mostly associated with the presence of ST gene determinant (14 from 22 fedA positive strains, 63.6%). Two strains possessed ST/Stx2v or LTI/Stx2v combination of genes for both toxins and two strains were negative for investigated toxin determinants. Among 8 fedA-negative strains, five strains without gene determinants for toxins were detected. All 30 E. coli strains were investigated for their binding to crude intestinal mucin of a weaned pig fixed in wells of microtitre plates. Positive mucin binding was observed in most of strains, however, great differences were shown between individual strains. Nineteen strains were classified as strongly adherent, 10 strains as weakly adherent, and only one nonadherent strain was found. Three E. coli strains, selected among the best mucin binders, bound to mucin in a concentration-dependent manner. A high mucin binding by E. coli strains was observed only after their cultivation on blood agar plates. Their cultivation in LB broth or on McConkey agar plates had negative effect on the mucin binding by these strains. The mucin binding is not restricted by the presence of fedA gene because the strains displaying very good binding are found either among fedA positive (1, 602/2, 4/3, 576/6) or fedA negative (DK 6, DK 8) E. coli strains. E. coli strains with the highest mucin binding ability belong to potential ST producents (strains 1, 602/2, 4/3, 6/2, 602/4) while the strains without genes coding toxin production displayed lower binding to mucin substratum with exception of the strains ZV5 and 13.

Escherichia coli strains from edema disease: O serogroups, and genes for Shiga toxin, enterotoxins, and F18 fimbriae

The objectives of the research were to determine the presence of the gene sequences for Shiga Toxin 2e (Stx2e), enterotoxins (ST-I, ST-II and LT-I), and F18 fimbriae in 144 Escherichia coli strains isolated from pigs with edema disease; to assess the ability of stx2e(+) strains to produce Stx2e; and to determine the O serogroups of the E. coli strains. Presence of the genes was determined by polymerase chain reaction (PCR), production of Stx2e was assessed by cytotoxicity for Vero and Hela cells, O serogroups were identified by agglutination with specific antisera. Of the 144 strains tested, 99 were stx2e(+) by PCR, but only 45 of these were Stx2e(+) in the cell culture assays. Among the 99 stx2e(+) strains, PCR detected the genes for F18ab, ST-I, ST-II, LT-I in 76, 40, 31 and 16 strains, respectively. Forty-one of the 99 sxt2e(+) strains belonged to O group 139; the rest did not belong to the classical edema disease O serogroups. It is likely that the enterotoxins, whose genes were detected at high frequency, are responsible for diarrhea seem in pigs with edema disease in Brazil.

Oedema disease is associated with metabolic acidosis and small intestinal acidosis

Limited information is available about the pathogenesis and pathophysiology of oedema disease (OD). Oedema disease is caused by specific enterotoxemic Escherichia coli (SLTIIv-toxin producing) strains; however, the same strains are also found in non-afflicted pigs. Furthermore, it is unclear how the 80 kDa SLTIIv-toxin can pass the intestinal barrier. In the present paper, piglets showing signs of acute OD were anaesthetised, instrumented and cardiovascular and intestinal parameters were determined at 0, 1, 2 and 3 hours. Healthy piglets from the same herd were used as a control. Cardiac output, blood pH and bicarbonate, small intestinal intramucosal pH, and (pulmonary) blood pressure were significantly lower in OD-pigs than in control pigs. It is concluded that OD is associated with metabolic and intestinal acidosis. Intestinal acidosis is known to increase macromolecular permeability. This suggests that once OD has developed, influx of SLTIIv-toxin into the blood stream is facilitated, thus perpetuating the disease. Since intestinal permeability appears to be central in OD, it is argued that post-weaning events increase intestinal permeability and predispose individuals to OD.

The AIDA autotransporter system is associated with F18 and stx2e in Escherichia coli isolates from pigs diagnosed with edema disease and postweaning diarrhea

Pathogenic Escherichia coli strains are known to cause edema disease (ED) and postweaning diarrhea (PWD) in piglets. Although the exact mechanisms of pathogenicity that lead to ED-PWD remain to be elucidated, E. coli-borne Shiga-like toxin and adhesion-mediating virulence factors such as F18 adhesin or F4 fimbriae are believed to play a central role in ED-PWD. In light of these observations we investigated whether another E. coli adhesin, the plasmid-encoded AIDA (adhesin involved in diffuse adherence) might also be present in ED-PWD-causing E. coli isolates. For rapid screening for the AIDA system in large numbers of isolates, a multiplex PCR method along with a duplex Western blot procedure was developed. When screening 104 strains obtained from pigs with or without ED-PWD, we observed a high prevalence of the AIDA operon in porcine E. coli isolates, with over 25% of all strains being AIDA positive, and we could demonstrate a significant association of the intact AIDA gene (orfB) with ED-PWD, while defects in orfB were associated with the absence of disease. Although our data hint toward a contribution of AIDA to ED-PWD, further studies will be necessary since the presence of the AIDA genes was also associated with the presence of the Shiga-like toxin and F18 adhesin genes, two reported virulence factors for ED-PWD.

[Main virulence factors in Escherichia coli isolates from swine over two weeks old with edema disease and/or E. coli diarrhea]

The OK antigens and the fimbriae F4 of E. coli with haemolysis isolated from 113 cases of oedema disease and/or diarrhoea were identified serologically. The genes for F18 and for enterotoxins LT, STIa and STII as well as Shigatoxin Stx2e were determined by PCR. Fimbrial variants F18ab and F18ac were distinguished by means of indirect immunofluorescence on smears prepared from the intestinal mucosa and from cultures grown under appropriate conditions. Adhesive fimbriae were detected with every case or isolate, respectively, by means of at least one out of the techniques mentioned above. The serogroup O149:K91 with fimbriae F4ac (K88ac) and genes for the enterotoxins LT and STII was most prevalent. Serogroup O139:K12 with fimbriae F18ab and the gene for Stx2e was second, whereas serogroups O141ab and O141ac with fimbriae F18ac and genes for Stx2e, STII and often LT were much less prevalent. The serogroup O147:K89 with fimbriae F18ac, and genes for STIa and STII was detected for the first time in Switzerland.

Edema disease as a model for systemic disease induced by Shiga toxin-producing E. coli

Edema disease (ED) is a naturally occurring disease of weaned pigs caused by host adapted strains of E. coli that produce Shiga toxin (STEC). We determined the temporal and quantitative relationships between intestinal colonization by STEC, levels of Shiga toxin (Stx2e) in the gut, in the blood, and clinical manifestations of ED. Bacterial colonization (10(8) CFU/cm ileum) was highest 4 days post inoculation (pi) in animals that did not develop clinical disease and 6 days pi in animals with clinical signs of ED. The mean time for the development of clinical signs of ED was 6 days pi (range 4-10). Average peak titers of Stx2e in the ileum were 1:16,384 in asymptomatic animals and 1:32,768 in clinical animals. Titers of Stx2e in the feces reflected the toxin titers in the ileum but were lower. Intestinal titers of Stx2e and the density of bacterial colonization were predictive of clinical ED for a group of animals but not for individuals. Approximately 50% of the pigs that had Stx2e titers of > or = 1:4096 and a bacterial density of > or = 10(6) CFU/cm in their ileum, had clinical ED. Pigs that had intestinal Stx2e titers < 1:4096 were asymptomatic. Stx2e was detected in the red cell fraction of blood from some of the pigs with clinical ED and in some that were asymptomatic. Stx2e was not detected in the serum of any animals. ED may be a useful model for predicting the temporal and quantitative relationships between bacterial colonization, Stx levels in the gut and blood and systemic disease for STEC in other species.

Edema disease

Edema disease is a common cause of illness and death loss in pigs during the first 2 weeks after weaning. The disease is an enterotoxemia caused by strains of E. coli that colonize the small intestine and produce Stx2e. Bacterial colonization is mediated by F18ab fimbriae. Susceptibility to disease is determined by presence of receptors for these fimbriae on small intestinal epithelial cells and is inherited as a dominant trait. Clinical signs and lesions are largely the result of Stx2e, which causes necrosis of endothelial and smooth muscle cells in small arteries and arterioles. Vascular damage in the brain stem with resultant infarction and malacia is the main cause of death in affected pigs. Studies conducted by veterinary researchers in the 1950s and 1960s identified the cause of the disease and provided future scientists with hypotheses to test regarding the pathogenesis. In the last two decades, studies using molecular-based techniques have allowed for the definitive identification of bacterial virulence factors that mediate intestinal colonization and vascular damage, that is, F18ab fimbriae and Stx2e. Identification of these virulence factors has provided a basis for current and future development of effective preventative measures, for example, vaccines.

Shiga toxin-producing Escherichia coli infection: temporal and quantitative relationships among colonization, toxin production, and systemic disease

Edema disease, a naturally occurring disease of swine caused by Shiga toxin-producing Escherichia coli (STEC), was used as a model for the sequence of events that occur in the pathogenesis of STEC infection. The mean time from production of levels of Shiga toxin 2e (Stx2e) detectable in the feces (day 1) to the onset of clinical disease (neurologic disturbances or death) was 5 days (range, 3-9). Bacterial colonization and titers of Stx2e in the ileum peaked at 4 days after inoculation in pigs without signs of clinical disease and at 6 days after inoculation in clinically affected pigs. Animals with the greatest risk of progressing to clinical disease tended to have the highest fecal toxin titers (>/=1:4096). Stx2e was detected in the red cell fraction from blood of some pigs showing clinical signs of edema disease but was not detected in the serum or cerebrospinal fluid.

Monoclonal antibodies recognising fimbriae F107 (F18) of an oedema disease causing strain of Escherichia coli

Escherichia coli isolated from experimentally induced oedema disease in pigs was used for the isolation and purification of F107 fimbriae. The reference strain was probed using membrane DNA hybridisation for the presence of fed A gene. F107 fimbriae were purified on FPLC and purity was checked on HPLC and SDS PAGE. A protein with major subunit of 18.9 kDa was used for Mabs preparation. Mabs reacted with 18.9 kDa protein previously classified as a major fimbrial subunit and were able to detect F107 fimbriae in immunoelectron microscopy on the surface of the strains 107/86 and 8872. Other strains used in this study did not express any fimbriae. Western blot analysis and F107 ELISA confirmed, that Mabs react with 18.9 kDa subunit whereas strains passaged many times in laboratory did not express F107 fimbriae.

Modeling the carbohydrate-binding specificity of pig edema toxin

The wild-type binding pentamer of Shiga-like toxin IIe (SLT-IIe) binds both the globotriaosylceramide (Gb3) and globotetraosylceramide (Gb4) cell surface glycolipids, whereas the double mutant GT3 (Q65E/K67Q) exhibits a marked preference for Gb3 [Tyrrell, G. J., et al. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 524-528]. We modeled three unique sites (sites 1-3) for binding of the carbohydrate moiety of Gb3 to GT3 and SLT-IIe, on the basis of the three sites observed for the SLT-I pentamer [Ling, H., et al. (1998) Biochemistry 37, 1777-1788]. Examination of the three sites in light of various mutation and binding data strongly suggested that one of the binding sites plays a role in the change of specificity observed for the GT3 mutant. We applied several modeling techniques, and developed a model for binding of the carbohydrate moiety of Gb4 to this site of the SLT-IIe binding pentamer. This model is consistent with a wide variety of mutation and binding data and clearly shows the importance of the terminal GalNAc residue of Gb4, as well as that of the two mutated residues of GT3, to the intermolecular interaction.

[A molecular test for the detection of E. coli F18 receptors: a breakthrough in the struggle against edema disease and post-weaning diarrhea in swine]

Oedema disease and post-weaning diarrhoea in swine are associated with the colonization of the intestine with toxigenic Escherichia (E.) coli bacteria of various serotypes. Colonization depends on specific binding between adhesive fimbriae and receptors on the enterocytes. The demonstration of these receptors allows the identification of susceptible and resistant pigs. Direct sequencing of the alpha (1,2) fucosyltransferase gene (FUT1) in swine being either susceptible or resistant to adhesion by F18 fimbriated E.coli revealed a mutation at basepair 307 (M307). Analysis of the mutation in Swiss Landrace and Large White families showed close linkage with the locus controlling resistance and susceptibility to E.coli F18 adhesion (ECF18R). The FUT1 (M307) mutation is a good marker for selection of E.coli of F18 adhesion resistant animals. The mutation is found with variable frequencies in Duroc, Hampshire and Pietrain pigs as well.

Molecular characterization of Escherichia coli strains isolated from pigs with edema disease

The present study was conducted to investigate the epidemiological relationship of isolates of Escherichia coli causing edema disease. Classical edema disease has not previously been described in Denmark, but between February 1994 and November 1995 cases appeared in 51 pig herds, among which direct or indirect trading contacts were confirmed for 36 of the herds. A total of 213 isolates from pigs with edema disease in Denmark and other countries and 23 E. coli O139 isolates from pigs with diarrhea or healthy pigs were analyzed to characterize their O serogroups, HindIII ribotypes, and pulsed-field gel electrophoresis (PFGE) types, and 183 of the isolates were also analyzed for their plasmid profiles. The resulting PFGE types of the isolates from pigs with edema disease were examined by cluster analysis. Ten isolates from three herds could not be typed with the available O antisera, whereas all other isolates were of serotype O139. However, all isolates from pigs with edema disease belonged to the same HindIII ribotype, which was not observed among the isolates from pigs with diarrhea or healthy pigs. All isolates from Danish pigs with edema disease except for three isolates originating from two herds belonged to the same or closely related XbaI PFGE types; the other three isolates were assigned to possibly related types. Isolates from pigs with edema disease in different countries belonged to different PFGE types. All isolates from Danish pigs with edema disease grouped together in one cluster, in contrast to isolates from other countries, which did not form any clusters. E. coli strains of serogroup O139 from pigs with diarrhea or isolated from the feces of healthy Danish pigs were very different. Plasmid profiles differed largely among isolates. However, among the isolates from Danish pigs with edema disease, one type predominated within herds. The present study indicated that most, if not all, of the observed cases of edema disease in Denmark were part of the same outbreak. The combination of PFGE typing and ribotyping was useful for studying the possible clonal relationship among strains, whereas plasmid profiling was less informative.

Biological relationship between F18ab and F18ac fimbriae of enterotoxigenic and verotoxigenic Escherichia coli from weaned pigs with oedema disease or diarrhoea

Comparative fimbrial expression and adhesion studies were made on enterotoxigenic and verotoxigenic E. coli (ETEC and VTEC) strains isolated from cases of porcine postweaning diarrhoea or oedema disease. F107(F18ab) fimbriae--monitored by polyclonal and monoclonal antibodies and by electron microscopy--were poorly expressed on most VTEC strains. In contrast, 2134P(F18ac) fimbriae were more readily detected on most ETEC strains. The F18ac strains adhered in vivo to ligated intestinal loops in weaned pigs while the F18ab strains did not adhere or adhered weakly. Similarly, the F18ac strains adhered to isolated intestinal brush borders in weaned pigs but the F18ab strains (except for the F107 reference E. coli) did not adhere or adhered weakly in vitro. Neither the F18ab nor F18ac strains adhered to brush borders from newborn pigs. In vitro adhesion of F18ab and F18ac strains was mannose resistant and receptors for F18 seemed to differ from receptors for K88(F4). It is concluded that the antigenic variants of F18 fimbriae (F18ab and F18ac) are biologically distinct. F18ab fimbriae are expressed poorly both in vitro and in vivo and are frequently linked with the production of SLT-IIv and serogroup O139, while F18ac are more efficiently expressed in vitro and in vivo and most often are linked with enterotoxin (STa, STb) production, and serogroups O141, O157.

Fine surface structure of enterotoxemic Escherichia coli O139:K12 strains associated with swine edema disease

The fine structure of the cell surface of seven enterotoxemic Escherichia coli (ETEEC) O139:K12 strains isolated from piglets with edema disease were examined electron microscopically using both the negative-staining method and the freeze-substitution fixation method. Densely packed, fine fibers were observed; they consisted of a capsule layer approximately 25 nm thick around the cell surfaces of strains 107/86, IW-2, ED-3, ED-43, and ED-61, all of which have a capacity to adhere strongly to HEp-2 cells. In contrast, no such structure was observed on the surface of strains RK-O139 or ED-1, both of which adhere only weakly to HEp-2 cells. These results suggest that the capsule structure might be associated with the ability to adhere to HEp-2 cells and, as a result, also potentially play some role in ETEEC infection.

Toxigenic Escherichia coli in Spanish piggeries from 1986 to 1991

Four-hundred and fourteen faecal samples from pigs with diarrhoea, oedema disease or healthy pigs, were collected from 65 piggeries located in different areas of Spain from 1986 to 1991. A total of 1334 Escherichia coli cultures were isolated from the pigs and studied for production of heat-labile (LT) and heat-stable (STa) enterotoxins, verotoxin (VT) and for type 1 (CNF1) and type 2 (CNF2) cytotoxic necrotizing factors. Strains producing enterotoxins (P < 0.001) or verotoxin (P < 0.05) were associated with enteric diseases of pigs. In the majority (82.3%) of piglets with strains, producing verotoxin the strains were also positive for production of STa enterotoxin. The most frequent toxin detected was STa. Although we isolated strains producing CNF1 from 1.5% of sick pigs, they were not statistically associated (P < 0.7) with enteric disease. Pigs may constitute a natural reservoir of CNF1 producing E. coli strains in Spain; their presence in the porcine intestine may be of significance in public health because such strains have been associated with human extraintestinal infections.

Purification and partial immunochemical characterization of proteins of fimbriae F107 from Escherichia coli isolated from edema disease of pigs

The paper describes the isolation, purification and characterization of F107-fimbrial proteins, obtained by thermoelution from Escherichia coli 107/86. Isolation of the pure F107 protein was done by FPLC chromatography, employing Superose 12, Mono Q, and Phenyl-Superose columns. The highest purity of the F107 protein was achieved with Superose 12 HR 10/30. Purity checking by a HPLC system Waters 625 LC (Millipore) proved the absence of protein admixtures in a fraction from Superose 12. Analysis of the molar mass of F107 proteins by SDS PAGE revealed that F107 fimbriae consist of two proteins, one of M = 43 kDa (minor), and other of M = 18.9 kDa (major). Western blot analysis with rabbit polyclonal antiserum confirmed that the 18.9 kDa protein was the major characteristic unit of F107 fimbriae.

[Adherence to HEp-2 cells of enterotoxemic Escherichia coli O-group 139 from pigs with edema disease]

One hundred and one strains of enterotoxemic Escherichia coli (ETEEC) O-group 139 isolated from swine with edema disease were investigated for their adherence to HEp-2 cells in the presence of D-mannose. All strains adhered in large numbers to the cells (21 to 60 bacteria/cell). No correlation was found between the presence of F107 fimbria on the organisms and the adherence to the cells. Adhesion-inhibition tests showed that anti-K12 serum inhibited the adhesion ETEEC O-group 139 (an inhibition rate of 63 to 65%), but anti-F107 or anti-O139 sera did not. These results indicate that the capsular K12 antigen may be one of the pathogenic factors of ETEEC O-group 139.

Restriction fragment length polymorphism and virulence pattern of the veterinary pathogen Escherichia coli O139:K82:H1

Escherichia coli O139:K82:H1 strains originating from outbreaks and single cases of oedema disease in pigs were characterized by their genomic restriction fragment length polymorphism (RFLP), their virulence pattern, and by the occurrence as well as the genomic distribution of the determinants for hemolysin (hly) and verotoxins (shiga-like toxins; sltI, sltII). Whereas the RFLPs revealed considerable variation among the E. coli O139:K82:H1 isolates depending the origin and epidemic source of the strains, the virulence gene slt II was found to be present in nearly all strains in a particular chromosomal region. Similar to RFLPs, the plasmid profiles are useful for epidemiological analysis.

Characterization of Escherichia coli strains isolated from pigs with edema disease

Escherichia coli strains belonging to serogroups O 138 and O 139 isolated from pigs with edema disease, were characterized with respect to the presence of genes encoding Shiga-like toxin I, Shiga-like toxin II and Shiga-like toxin IIv (SLT I, SLT II and SLT IIv). Genes coding for the heat-stable and heat-labile enterotoxins (ST I and LT I) were also detected. Plasmid profiling, restriction enzyme digestion of total DNA, and ribotyping were performed for further characterization of the strains. The oligonucleotide probes applied in this study appeared to be useful tools for detecting genes coding cytotoxins and enterotoxins. DNA from 12 of 16 strains hybridized with two SLT II probes, and DNA from two SLT IIv encoding strains also hybridized with the ST I probe. DNA from one SLT IIv negative strain hybridized with the LT I probe. The results from plasmid profiling, restriction enzyme digestion, and ribotyping were compared with serogrouping in attempts to distinguish between the different E. coli edema disease isolates. Fourteen different plasmid profiles were identified, and as restriction patterns barely did, and ribotyping patterns did not, reveal any information useful for differentiation of the strains beyond serogroup level, plasmid profiling seemed to be the most suitable method for discrimination between the edema disease strains investigated here.

Characteristics of the Shiga-like toxin produced by Escherichia coli associated with porcine edema disease

Shiga-like toxin (SLT-IIv) from Escherichia coli strains associated with edema disease of pigs was characterized and compared with SLT-I, SLT-II, and the SLT of E. coli strain HI8 (SLT-HI8). SLT-IIv from an E. coli K12 in which the genes for SLT-IIv had been cloned was indistinguishable from SLT-IIv of wild strains of E. coli from edema disease. There was cross-neutralization among all SLTs except SLT-I. The different SLTs could be distinguished by heat lability, with the descending order of heat lability being SLT-IIv, SLT-II, SLT-I, and SLT-HI8. SLT-IIv and SLT-HI8 had lower cytotoxic titers on HeLa cells compared with Vero cells and were more active on MDBK cells than were the other SLTs. All SLTs were enterotoxic in rabbit but not in pig intestine and SLT-IIv was less enterotoxic than SLT-I. SLT-IIv had a lower LD50 in mice than did the other SLTs.

Effects of Escherichia coli Shiga-like toxins (verotoxins) in pigs

Escherichia coli K12 strains TB1(pCG5), with the genes for Shiga-like toxin IIv from an edema disease isolate of E. coli and TB1(pCG5-1), with the toxin genes inactivated by transposon mutagenesis, were used to test the hypothesis that Shiga-like toxin IIv was the same as edema disease principle. Ammonium sulfate precipitated culture supernatants from the pair of E. coli K12 strains and from a wild edema disease isolate of E. coli (E145) were tested for their ability to induce signs and lesions of edema disease in intravenously inoculated weaned pigs. Similar preparations from E. coli which produce Shiga-like toxins I and II were also tested. Preparations from E. coli TB1 (pCG5) and E145 contained high levels of Shiga-like toxin IIv and induced signs and lesions similar to those seen in edema disease, whereas preparations from E. coli TB1 (pCG5-1) failed to induce signs or lesions of edema disease. All Shiga-like toxin preparations produced delayed neurological signs, fibrinoid necrosis of arterioles and hemorrhages in the cerebellum of pigs. High doses of Shiga-like toxin IIv were associated with superficial necrosis of the colonic epithelium and vasculitis. Shiga-like toxins I and II resulted in kidney lesions but no enteric pathology. Shiga-like toxin II preparations had the lowest median lethal dose for pigs, Shiga-like toxin IIv was intermediate and Shiga-like toxin I was the least toxic.

Detection and identification of pathotypes of verocytotoxigenic Escherichia coli isolated from weaned piglets using gene probes for seven E. coli toxins

Seventy verocytotoxigenic (VTEC) and sixty-three non VTEC haemolytic Escherichia coli isolated from recently weaned piglets were examined by the colony hybridization assay using gene probes for three verocytotoxins: Edema disease principle (EDP) and Shiga-like toxins I and II (SLTI and SLTII). The results with the EDP and SLTII probes were identical. All VTEC hybridized with these two probes, while non VTEC did not. All 133 E. coli were negative for the SLTI probe. Hybridization of the plasmid content of 14 VTEC did not show any evidence for plasmid localization of the genes coding for the EDP. The 70 VTEC were also assayed with gene probes for heat-stable (STaP, STb) and heat-labile (LT, LTIIa) enterotoxins. Only the STb probe was hybridized by 36 of them. Most STb-positive isolates belonged to serotype O141: K85 biotypes 9 and 13 PC.

Edema disease-like brain lesions in gnotobiotic piglets infected with Escherichia coli serotype O157:H7

Gnotobiotic piglets inoculated with Escherichia coli serotype O157:H7 strains that produced Shiga-like toxin II developed brain lesions similar to those observed in edema disease of swine, including arteriolar necrosis and malacia. Loss of ability to produce Shiga-like toxin II resulted in loss of ability to cause brain lesions.

Verotoxin production among porcine strains of Escherichia coli and its association with oedema disease

Strains of Escherichia coli isolated from documented cases of disease in pigs and belonging to a wide range of pathogenic serotypes were tested for their ability to produce a heat labile verotoxin (VT). The strains isolated from oedema disease all produced VT, indicating that the cytotoxin detected by the vero-cell assay was identical to "oedema disease principle". Strains belonging to the serotypes associated with enterotoxic diarrhoea were VT-. Not all the strains belonging to the recognised oedema disease serotypes (O141:K85, O139:K82 and O138:K81) produced VT, but the VT- strains were not associated with outbreaks of clinical disease.