Expression and plasmid transfer of genes coding for the fimbrial antigen F107 in porcine Escherichia coli strains

Wild Boars as Reservoir of Highly Virulent Clone of Hybrid Shiga Toxigenic and Enterotoxigenic Escherichia coli Responsible for Edema Disease, France

Edema disease is an often fatal enterotoxemia caused by specific strains of Shiga toxin–producing Escherichia coli (STEC) that affect primarily healthy, rapidly growing nursery pigs. Recently, outbreaks of edema disease have also emerged in France in wild boars. Analysis of STEC strains isolated from wild boars during 2013–2019 showed that they belonged to the serotype O139:H1 and were positive for both Stx2e and F18 fimbriae. However, in contrast to classical STEC O139:H1 strains circulating in pigs, they also possessed enterotoxin genes sta1 and stb, typical of enterotoxigenic E. coli. In addition, the strains contained a unique accessory genome composition and did not harbor antimicrobial-resistance genes, in contrast to domestic pig isolates. These data thus reveal that the emergence of edema disease in wild boars was caused by atypical hybrid of STEC and enterotoxigenic E. coli O139:H1, which so far has been restricted to the wildlife environment.

Supplementation with Lactobacillus paracasei or Pediococcus pentosaceus does not prevent diarrhoea in neonatal pigs infected with Escherichia coli F18

Infectious diarrhoea is a worldwide problem in newborns. Optimal bacterial colonisation may enhance gut maturation and protect against pathogenic bacteria after birth. We hypothesised that lactic acid bacteria (LAB) administration prevents pathogen-induced diarrhoea in formula-fed newborns. Newborn caesarean-delivered, colostrum-deprived term piglets on parenteral nutrition for the first 15 h, were used as models for sensitive newborn infants. A commercially available probiotic strain, Lactobacillus paracasei F19 (LAP, 2·6×108 colony-forming units (CFU)/kg per d) and a novel LAB isolate, Pediococcus pentosaceus (PEP, 1·3×1010 CFU/kg per d), were administered for 5 d with or without inoculation of the porcine pathogen, Escherichia coli F18 (F18, 1010 CFU/d). This resulted in six treatment groups: Controls (n 9), LAP (n 10), PEP (n 10), F18 (n 10), F18-LAP (n 10) and F18-PEP (n 10). The pathogen challenge increased diarrhoea and density of F18 in the intestinal mucosa (P<0·05). LAB supplementation further increased the diarrhoea score, relative to F18 alone (P<0·01). Intestinal structure and permeability were similar among groups, whereas brush border enzymes were affected in variable intestinal regions with decreased activities in most cases after F18 and LAB inoculation. Bacterial density in colon mucosa increased after F18 inoculation (P<0·05) but was unaffected by LAB supplementation. In colon contents, acetic and butyric acids were increased by PEP (P<0·05). The LAB used in this study failed to reduce E. coli-induced diarrhoea in sensitive newborn pigs. In vulnerable newborns there may be a delicate balance among bacterial composition and load, diet and the host. Caution may be required when administering LAB to compromised newborns suffering from enteric infections.

α1,2-Fucosyllactose Does Not Improve Intestinal Function or Prevent Escherichia coli F18 Diarrhea in Newborn Pigs

OBJECTIVES

Infectious diarrhea, a leading cause of morbidity and deaths, is less prevalent in breastfed infants compared with infants fed infant formula. The dominant human milk oligosaccharide (HMO), α-1,2-fucosyllactose (2'-FL), has structural homology to bacterial adhesion sites in the intestine and may in part explain the protective effects of human milk. We hypothesized that 2'-FL prevents diarrhea via competitive inhibition of pathogen adhesion in a pig model for sensitive newborn infants.

METHODS

Intestinal cell studies were coupled with studies on cesarean-delivered newborn pigs (n = 24) without (control) or with inoculation of enterotoxigenic Escherichia coli F18 (7.5 × 10/day for 8 days) fed either no (F18) or 10 g/L 2'-FL (2FL-F18).

RESULTS

In vitro studies revealed decreased pathogen adhesion to intestinal epithelial cells with 2'-FL (5 g/L; P < 0.001). F18 pigs showed more diarrhea than control pigs (P < 0.01). Administration of 2'-FL to F18 pigs failed to prevent diarrhea, although the relative weight loss tended to be reduced (-19 vs -124 g/kg, P = 0.12), higher villi were observed in the distal small intestine (P < 0.05), and a trend toward increased proportion of mucosa and activities of some brush border enzymes in the proximal small intestine. In situ abundance of α-1,2-fucose and E coli was similar between groups, whereas sequencing showed higher abundance of Enterobacteriaceae in F18, Enterococcus in control and Lachnospiraceae in 2FL-F18 pigs.

CONCLUSIONS

2'-FL inhibited in vitro adhesion of E coli F18 to epithelial cells, but had limited effects on diarrhea and mucosal health in newborn pigs challenged with E coli F18.

Fimbriae: Classification and Biochemistry

Proteinaceous, nonflagellar surface appendages constitute a variety of structures, including those known variably as fimbriae or pili. Constructed by distinct assembly pathways resulting in diverse morphologies, fimbriae have been described to mediate functions including adhesion, motility, and DNA transfer. As these structures can represent major diversifying elements among Escherichia and Salmonella isolates, multiple fimbrial classification schemes have been proposed and a number of mechanistic insights into fimbrial assembly and function have been made. Herein we describe the classifications and biochemistry of fimbriae assembled by the chaperone/usher, curli, and type IV pathways.

Polymerase chain reaction-based method for the typing of F18 fimbriae and distribution of F18 fimbrial subtypes among porcine Shiga toxin-encoding Escherichia coli in Germany

Edema disease is an enterotoxemic disorder of weaned piglets that represents a significant threat to pig husbandry worldwide. The causative Escherichia coli strains are highly adapted to the porcine host and characterized by the production of Shiga toxin type 2e (Stx2e) and adhesive F18 fimbria. The current study assessed the occurrence of F18 fimbrial subtypes in 241 porcine stx2e(+) fedA(+) E. coli strains in Germany, including 116 Shiga toxin-encoding E. coli (STEC) and 125 Shiga toxin E. coli/enterotoxigenic E. coli (STEC/ETEC) isolates. In addition, a novel multiplex polymerase chain reaction (PCR) was developed in order to improve the typing system in terms of costs, time, and discriminative power. Utilizing the novel F18 typing PCR, 93 E. coli strains (38.5%) tested positive for the F18ab fimbrial subtype and 147 strains (61.0%) for the F18ac fimbrial subtype, while 1 strain remained nontypeable. Six strains were classified as F18ac using the F18 typing PCR, but were classified as F18ab using the F18-restriction fragment length polymorphism assay. Nucleotide sequencing of the FedA gene revealed that 5 of these strains encoded F18ac fimbriae, while the FedA of 1 strain did not cluster with F18ab or with F18ac amino acid sequences. The F18 fimbrial subtype was significantly associated with the pathovar of the E. coli strains, as 73.2% of the STEC isolates harbored F18ab genes whereas 93.6% of the STEC/ETEC isolates proved F18ac positive. In conclusion, the novel F18 typing PCR allows a specific identification of the F18 fimbrial subtype. The genetic and phenotypic heterogeneity of F18 fimbriae in porcine E. coli strains should be considered in the development of new vaccines and diagnostic tools.

Prevalence of enterotoxigenic Escherichia coli virulence genes from scouring piglets in Zimbabwe

World-wide, enterotoxigenic Escherichia coli (ETEC) and verotoxigenic E. coli (VTEC)-induced diarrhea are economically important for porcine producers. Our aim was to investigate the prevalence of toxin and fimbrial genes among E. coli isolated from diarrheic piglets from randomly selected piggeries in Zimbabwe. We used multiplex PCR for screening STa, STb, LT, and Stx-2e toxins. Subsequently F4, F5, F6, F18 and F41 fimbriae genes were screened in toxin positive isolates. Toxin positive strains lacking tested fimbriae genes were characterized using transmission electron microscopy, agglutination and agglutination inhibition tests. Approximately 32% of the 1,984 isolates tested positive for STa, STb, LT or Stx-2e genes. Of these, approximately 81% had F4, F5, F6, F18 or F41 fimbriae genes. The remaining toxin positive strains lacked tested fimbriae genes and appeared to either express F1-like fimbriae, or lacked fimbriae. The data constitute an important framework for implementation of prevention measures, such as using relevant fimbriae-based vaccines against ETEC induced diarrhea or VTEC-induced edema.

Evolution of the chaperone/usher assembly pathway: fimbrial classification goes Greek

Many Proteobacteria use the chaperone/usher pathway to assemble proteinaceous filaments on the bacterial surface. These filaments can curl into fimbrial or nonfimbrial surface structures (e.g., a capsule or spore coat). This article reviews the phylogeny of operons belonging to the chaperone/usher assembly class to explore the utility of establishing a scheme for subdividing them into clades of phylogenetically related gene clusters. Based on usher amino acid sequence comparisons, our analysis shows that the chaperone/usher assembly class is subdivided into six major phylogenetic clades, which we have termed alpha-, beta-, gamma-, kappa-, pi-, and sigma-fimbriae. Members of each clade share related operon structures and encode fimbrial subunits with similar protein domains. The proposed classification system offers a simple and convenient method for assigning newly discovered chaperone/usher systems to one of the six major phylogenetic groups.

Rapid identification of virulence genes in enterotoxigenic Escherichia coli isolates associated with diarrhoea in Queensland piggeries

OBJECTIVE

To identify virulence genes in enterotoxigenic E coli (ETEC) isolates associated with diarrhoea in neonatal, 1 to 3 week-old and weaned pigs in southeast Queensland.

DESIGN

Multiplex PCR and serotyping were applied to E coli isolates obtained over a 5-year period (1998-2002) from cases diagnosed at Toowoomba Veterinary Laboratory.

PROCEDURE

A total of 126 isolates from 25 different Queensland piggeries were tested for haemolytic activity on 5% sheep blood agar and by multiplex PCR for the presence of five commonly recognised fimbrial (F4, F5, F6, F41 and F18) and three enterotoxin genes (STa, STb, LT). A subset of 62 representative isolates were serotyped by slide agglutination. For comparative purposes, multiplex PCR was also performed on the DNA of 31 ETEC isolates from 9 serotypes originating from piggeries in southern New South Wales.

RESULTS

A total of 113 (89.7%) of the isolates from Queensland possessed ETEC virulence genes, including 14 of 15 isolates from neonatal pigs (93.3%), 18 of 23 isolates from 1 to 3 week old pigs (78.3%) and 81 of 88 isolates from weaned pigs (92.1%). F4:STa:STb:LT (serotype O149) was the most prevalent pathotype in neonatal and 1-3 week old pigs and F4:STa:STb:LT (serotype O149) and F18:STa:STb:LT (serotype O141) were most prevalent in weaned pigs. In comparison, isolates obtained from neonatal pigs from New South Wales belonged to a more diverse range of pathotypes and serotypes.

CONCLUSION

Multiplex PCR was a rapid and specific method for detecting the presence of ETEC virulence genes in porcine E coli isolates. For isolates obtained from cases of suspected colibacillosis in Queensland, growth of a heavy pure culture of haemolytic E coli was a sensitive prognostic indicator of the presence of ETEC virulence genes in the isolate. ETEC pathotypes and serotypes remained stable in Queensland piggeries over the five-year study period and appear to have changed little over the last three decades.

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).

Association between the porcine Escherichia coli F18 receptor genotype and phenotype and susceptibility to colonisation and postweaning diarrhoea caused by E. coli O138:F18

Porcine postweaning Escherichia coli enteritis is a cause of significant morbidity and mortality in pigs worldwide, and effective prevention remains an unsolved problem. This study examined the correlation between susceptibility of pigs to experimental infection with an E. coli F18 strain and the porcine intestinal F18 receptor genotypes. Thirty-one pigs classified as either belonging to the susceptible or the resistant genotype were inoculated with cultures of an E. coli O138:F18 isolated from a pig with postweaning diarrhoea. Susceptibility to colonisation and diarrhoea was assessed by clinical observations, faecal shedding of the challenge strain, histopathology and microscopic adhesion tests. Ten of 14 (71.4%) genetically susceptible pigs and one of 17 (5.9%) resistant pigs developed diarrhoea attributable to the challenge strain. There was no difference in susceptibility between homozygotic and heterozygotic susceptible pigs. Faecal shedding of the challenge strain correlated with the genetic receptor profile. Twenty pigs examined immunohistochemically revealed focal to extensive small intestinal mucosal colonisation by E. coli O138:F18 in nine of 10 susceptible and three of 10 resistant pigs. Results of in vitro adhesion assays performed with F18 cells on enterocyte preparations from 24 pigs, showed complete concordance with the F18 genotypes. In conclusion, this study showed a high correlation between the porcine intestinal F18 receptor genotypes and susceptibility to disease. However, pigs of the resistant F18 receptor genotype were not entirely protected against intestinal colonisation by E. coli F18.

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.

Automated 5' nuclease assay for detection of virulence factors in porcine Escherichia coli

This paper describes the development of a 5' nuclease assay for detection of virulence factor genes responsible for colonization factors and toxins in Escherichia coli isolated from pigs. Colonization factors were F4, F5, F6, F18, F41 and the outer membrane protein intimin. Toxins were heat stable (STa, STb, EAST1) and heat labile (LT) enterotoxins and the verocytotoxin variant 2e (VT2e). To correctly identify false negative results, an endogenous internal control targeting the E. coli 16 S rRNA gene was incorporated in each test tube. The assay was evaluated using a collection of E. coli reference strains which have previously been examined with phenotypical assays or DNA hybridization. Furthermore, the assay was evaluated by testing porcine E. coli field strains, previously characterized. The 5' nuclease assay correctly detected the presence of virulence genes in all reference strains. When testing field strains there was generally excellent agreement with results obtained by laboratories in Belgium and Germany. In conclusion, the 5' nuclease assay developed is a fast and specific tool for detection of E. coli virulence genes in the veterinary diagnostic laboratory.

Polyclonal sandwich ELISAs to detect F18 fimbriated Escherichia coli in pigs in Northern Ireland

F18 fimbriated Escherichia coli are a newly described cause of postweaning diarrhea in pigs. Polyclonal rabbit antisera were raised to the antigenic variants, F18ab and F18ac, of these fimbriae and were used to develop monospecific sandwich enzyme-linked immunosorbent assays (ELISAs). The ELISAs were standardized with type cultures characterized by polymerase chain reaction techniques (PCR) and then used to conduct a study of the prevalence of F18 fimbriated E. coli in pigs in Northern Ireland. A total of 176 isolates were tested by ELISA and PCR. Eight isolates were positive for F18 by ELISA, of which 2 were shown to be false positives by PCR and one was PCR positive but ELISA negative. Of the 6 confirmed ELISA positives, all produced VT2 toxin and 3 produced ST toxin. Four positives were from serogroups O138 and O139, previously associated with porcine diarrhea.

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.

Purification and characterization of the fimbria F18ac (2134P) isolated from enterotoxigenic Escherichia coli (ETEC)

The adhesin F18ac purified on Sepharose CL 4B column chromatography and SDS-PAGE stained with Coomassie Blue and Western blotting using specific anti-F18ac serum presented one band of approximately 17kDa. Gold immunolabeling revealed that the adhesin F18ac has a fimbrial structure on the bacterial surface. The first 27 amino acid residues of the N-terminal portion of the adhesin F18ac, showed 92.5% homology (25 amino acids) with the F107 (F18ab) fimbriae.

Active oral immunization of suckling piglets to prevent colonization after weaning by enterotoxigenic Escherichia coli with fimbriae F18

Immunoprophylaxis of porcine oedema disease and post-weaning diarrhoea caused by strains of Escherichia coli expressing fimbriae F18 is an unsolved problem. The study was designed to examine whether vaccination with a live F18ac vaccine of unweaned pigs born to sows with F18ac antibody in the colostrum requires preformed fimbriae in the vaccine, and whether protection against the heterologous fimbrial variant F18ab is induced as well. Genetically susceptible pigs were vaccinated orally on three consecutive days, beginning 10 days before weaning with 10(11) CFU of an F18ac culture. Challenge with a dose of 10(7) CFU of E. coli F18 on three consecutive days was initiated 9 or 11 days after weaning. Eighteen pigs given the fimbriated F18ac vaccine and challenged with a strain of the homologous fimbrial variant were protected against colonization; mean faecal viable counts of the challenge strain were >3 log10 lower than those from the 17 non-vaccinated control pigs. The vaccinated pigs developed a significant rise of F18ac IgA serum antibodies. The 23 pigs which had received the non-fimbriated vaccine showed no significant protection and exhibited much lower serum F18ac IgA ELISA reactivities. Eighteen pigs vaccinated with the fimbriated F18ac and challenged with an F18ab strain had faecal viable counts nearly as high as those from 16 non-vaccinated control pigs. It is concluded that only oral vaccines having preformed fimbriae induce protection limited to the homologous fimbrial variant.

Prevalence of virulence factors of Escherichia coli strains isolated from diarrheic and healthy piglets after weaning

This study determined the prevalence of F4, F5, F6, F17 and F41 fimbriae and the genes for FedA (F18 fimbriae), LT and ST enterotoxins, and Shiga toxins Stx1, Stx2 and Stx2e among E. coli isolated from 372 weaned pigs with diarrhea and 46 healthy pigs of the same age. Agglutination tests showed that most isolates were negative for all five fimbrial antigens. The F4 antigen was found in 71 (19.1%) and the F5, F6, or F41 antigen was detected in 6.4% of isolates from diseased pigs. Genes for the F18 fimbriae were detected in 10 (2.7%) strains from diarrheic pigs and in 1 of 46 isolates from healthy pigs. Most isolates (213, 57.3%) from pigs with diarrhea were positive for LTI only or for LTI and STI or Stx2e toxin genes. Fifteen strains (13.7%) possessed only the STI or STII toxin genes. All F4-positive bacteria had genes for LTI or LTI and STI, whereas F18-positive isolates had genes for LTI, LTI/STI, or LTI/Stx2e. Of the strains isolated from diseased pigs, 264 (71.0%) were negative for the fimbrial antigens (genes) examined in this study. The fimbria-negative isolates frequently possessed genetic determinants for LTI (118, 31.7%) or for STII (16, 4.3%) enterotoxins.

The use of polymerase chain reaction for determination of virulence factors of Escherichia coli strains isolated from pigs in Poland

E. coli strains isolated from pigs with postweaning diarrhea or edema disease were tested by phenotypic and genotypic methods for the presence of virulence antigens and genes, respectively. The slide agglutination and ELISA analyses were used for determination of F4, F5, F6, F17, and F41 fimbriae whereas the prevalence of fimbrial fedA and toxin eltI, estI, estII, stx1, stx2 and stx2e genes were recorded by the means of PCR. Only F4 antigen (ac variant) was found in strains of the serogroup O149:K91 isolated from pigs with diarrhea. PCR analyses showed that the fedA gene encoding F18 fimbriae was present in 61.9% of strains isolated from pigs with diarrhea and in 84.2% of strains isolated from pigs with edema disease. The eltI genes encoding heat-labile toxin I (LTI) were present only in 9 out of 21 strains recovered from pigs with diarrhea. Shiga toxin 2 variant (stx2e) genes were found in six isolates from edema disease and also in one strain from diarrhea. The PCR test used in the study was a sensitive and valuable method for determination of virulence factors of E. coli strains.

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.

Genetic diversity among Escherichia coli isolates carrying f18 genes from pigs with porcine postweaning diarrhea and edema disease

Multilocus enzyme electrophoresis was applied to detect allelic variation and multilocus genotypes (electrophoretic types [ETs]) among 43 Escherichia coli isolates from weaned pigs suffering from edema disease or from diarrhea. ETs were analyzed in relation to O serogroups and virulence genes (sta, stb, lt, stx2, and f18) by DNA hybridization. Genomic diversity was the lowest in serogroup O138, while virulence genes (stx2 and f18) were the most uniform in serogroup O139. In general, the serogroups or toxin and F18 fimbria types were not related to selected ETs, suggesting that the toxin and f18 fimbria genes in E. coli isolates from pigs with postweaning diarrhea or edema disease occur in a variety of chromosomal backgrounds.

Differentiation of F18ab+ from F18ac+ Escherichia coli by single-strand conformational polymorphism analysis of the major fimbrial subunit gene (fedA)

Toxin-producing Escherichia coli expressing F18 fimbriae colonizes the small intestines of weaned pigs and causes diarrhea, edema disease, or both. The F18 family is composed of two antigenic variants, F18ab and F18ac. Because many strains do not express F18 fimbriae in vitro, identification and differentiation of these two variants are difficult. Single-strand conformational polymorphism (SSCP) analysis is a rapid method for identifying genetic mutations and polymorphisms. The F18 major fimbrial subunit genes (fedA) of 138 strains were amplified by PCR, and genetic differences were detected by SSCP analysis. The SSCP analysis of the fedA gene differentiated F18ab+ strains from F18ac+ strains. Most strains classified as F18ab+ by SSCP analysis contained Shiga toxin 2e and enterotoxin genes. Most strains classified as F18ac+ by SSCP analysis contained only enterotoxin genes. The SSCP analysis was a useful method for predicting the antigenicity of F18+ E. coli and could also be used for analysis of other virulence genes in E. coli and other pathogenic bacteria.

Effect of oral egg antibody in experimental F18+ Escherichia coli infection in weaned pigs

The protection conferred by egg antibody specific for F18-fimbriae against infection with F18+ Escherichia coli was studied in controlled passive immunization trials involving weaned pigs. Parameters of protection consisted of body weight gain, frequency and severity of diarrhea and recovery of the challenge strain of F18+ E. coli. Weaned pigs at four weeks of age were challenge exposed once daily for three days by oral inoculation with 10(11) cfu of virulent F18+ E. coli followed by daily administration of antibody supplemented feed for 9 days starting from the first challenge day 0. Results showed a dose-dependent response to antibody treatment. The group of pigs given 1:50 titer of antibody in feed had less frequency of diarrhea (P < 0.01-0.05), higher rate of gain (P < 0.01) and lower isolation rate of challenge strain in rectal and intestinal swabs (P < 0.01) compared to non-treated control. In the same manner, the anti-F18 antibody significantly reduced adherence of F18+ E. coli to pig intestinal epithelial cells in vitro (P < 0.01). Results suggest that egg antibodies specific for the F18 fimbriae is a suitable immunotherapeutic agent for pigs infected with F18+ E. coli and that pigs can be protected from overt clinical disease and the subsequent reduced performance arising from infection with this pathogen.

Reduced intestinal colonisation with F18-positive enterotoxigenic Escherichia coli in weaned pigs fed chicken egg antibody against the fimbriae

Newly weaned pigs were fed a basal diet containing either egg antibody against fimbriae F18 at a high or low level, control egg powder or no egg, and challenged with enterotoxigenic Escherichia coli with fimbriae F18. The challenge was repeated after termination of the antibody treatment. Antibody-containing egg powder was produced by vaccination of hens with semi-purified fimbriae of the two variants F18ab and F18ac. Pigs eating egg powder with antibody against the same fimbrial variant were fully protected, even if the vaccine for the hens was produced with a different serotype devoid of enterotoxins. The effect was dose-dependent. The high dose of antibody against the heterologous variant of fimbriae F18 reduced colonisation at a level which was not significant. Ingestion of egg antibody partially suppressed the build-up of anti-colonisation immunity. Oral application of egg antibodies offers a promising approach for the prevention of infectious diseases of the digestive tract.

Role of fimbriae F18 for actively acquired immunity against porcine enterotoxigenic Escherichia coli

Enterotoxigenic (ETEC) and enterotoxaemic (ETEEC) Escherichia (E.) coli that express F18 (F107) fimbriate colonize the small intestine and cause diarrhoea and/or oedema disease in weaned pigs. So far, two antigenic variants of F18 can be distinguished with a common antigenic factor designated 'a' and two specific factors called 'b' and 'c'. In this study the existence of crosswise anti-colonization immunity between E. coli strains that express F18ab or F18ac fimbrial variants, respectively, was demonstrated. Weaned pigs of susceptible genotype with respect to susceptibility to adhesion of E. coli with fimbriae F18 were inoculated with E. coli strains 3064STM (0157:K-:H-:F18ab; resistant to streptomycin) and 8199RIF (0141ab:K-:H4:F18ac; resistant to rifampicin). The faecal shedding was compared subsequent to immunization and homologous or heterologous challenge. An enzyme-linked immunosorbent assay (ELISA) was applied to measure IgA, IgM and IgG antibodies against the F18ab and F18ac antigens in saliva, faeces, serum and intestinal wash samples. About 8 log CFU/g of the inoculated strains were found in faeces of all pigs following immunization as well as in non-immunized controls after challenge. Bacterial counts of the inoculated strains after challenge were between 2 and 5 log lower, without any difference between homologous and heterologous challenge. Intestinal colonization with fimbriated E. coli resulted in production of significantly increased levels of anti-fimbrial antibodies, especially IgA, in serum and intestinal wash samples. There were higher levels of homologous than of heterologous anti-fimbrial antibodies. Production of antibodies against F18a or against another common fimbrial antigen is probably responsible for crosswise anti-colonization immunity between E. coli strains with F18ab and F18ac fimbrial variants. Serum F18-specific IgA may be a useful indicator of a mucosal immune response directed against F18 fimbriae.

Fimbrial colonisation factors F18ab and F18ac of Escherichia coli isolated from pigs with postweaning diarrhea and edema disease

During the last 5 years at least four new types of colonisation factors have been described in association with porcine postweaning diarrhea and edema disease strains of E. coli. Recently, evidence was presented that these fimbrial factors are closely related to each other, and therefore the common denomination F18 was proposed. Until now, two variants F18ab and F18ac were identified that can be distinguished by serology. Alternatively, to circumvent elaborate growth conditions for the optimal expression of F18 fimbriae in vitro, PCR and subsequent restriction enzyme digestion of the amplification product can be used to differentiate F18ab from F18ac positive isolates. Reports that studied the prevalence of F18 positive E. coli show that this factor is present in about 30% to more than 50% of the PWD or ED strains negative for F4, F5, F6 or F41. Susceptibility of pigs to colonisation depends on the availability of intestinal receptors, and is under the control of a chromosomal locus. In young pigs susceptibility increases with age. Intestinal infection with F18 positive E. coli induces protection against repeated colonisation with E. coli bearing the homologous or the heterologous fimbrial variant of F18. Finally, preliminary passive protection studies suggest that F18 antibodies inhibit the colonisation of the pig's intestine by F18ab and F18ac positive strains.

Prevalence of the fimbrial antigens F18 and K88 and of enterotoxins and verotoxins among Escherichia coli isolated from weaned pigs

Until recently, the fimbrial F18 antigen has been provisionally designated F107, 2134P, or 8813. Using the slide agglutination test, this antigen was shown to be present on 139 of 160 Escherichia coli strains of type O139:K82 and on all of the 146 K88-negative strains of the other pathogenic porcine serotypes. These strains were isolated from weaned pigs which in most cases had died from postweaning colibacillosis. All strains were haemolytic. With only three exceptions, they produced verotoxin and/or enterotoxin. The F18ab variant strongly predominated on the O139:K82 strains and was found on about half of the O138:K81 strains and a few O157 strains, whereas the other strains carried the F18ac variant. In serotypes which can carry either F18 or K88 fimbriae, closer clonal relationships between the strains associated with F18 and those associated with K88 were missing.

Designations F18ab and F18ac for the related fimbrial types F107, 2134P and 8813 of Escherichia coli isolated from porcine postweaning diarrhoea and from oedema disease

The relatedness of the fimbriae produced by eight E. coli strains including type strains with F107 fimbriae, 2134P pili and colonization factor 8813 (preliminary F18), was examined. These strains had been isolated principally from pigs which were affected with postweaning diarrhoea or with oedema disease. The fimbriae were analyzed by means of electron microscopy, slide agglutination, immunofluorescence, immunogold labelling, immuno-diffusion, immunoelectrophoresis and western blot, molecular genetic techniques, and in vitro adhesion. The fimbriae of all the strains were long flexible filaments with a diameter not larger than 4.6 nm showing a zig-zag pattern. Results obtained by the serological techniques confirmed that the fimbriae possessed a common antigenic determinant designated 'a' in addition to a variant-specific determinant designated 'b' or 'c'. Immunoelectron microscopy demonstrated that the determinants 'a' and 'b' or 'a' and 'c' were localized along the same fimbrium. In immunoelectrophoresis, fimbrial extracts of selected strains yielded a single precipitation line towards the cathode. One single major subunit of approximately 15 kDa was recognised in western blots by antisera against the common antigenic determinant and the variant specific determinants. All strains possessed sequences related to gene fedA, coding for the major subunit of fimbriae F107. Two types of fedA-related subunit genes were differentiated, corresponding to the 'ab' and 'ac' types of fimbriae as defined by serological methods. The results demonstrated that F107 fimbriae, 2134P pili and colonization factor 8813 are related, and that two serological variants can be distinguished. We propose designations F18ab (for F107), and F18ac (for 2134P and 8813) in analogy to the nomenclature of F4 fimbriae.