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

Mapping the neutralizing epitopes of F18 fimbrial adhesin subunit FedF of enterotoxigenic Escherichia coli (ETEC)

K88 and F18 fimbrial enterotoxigenic Escherichia coli (ETEC) are the major causes of post-weaning diarrhea (PWD) in pigs. A vaccine that induces broad immunity to prevent K88 and F18 fimbrial ETEC bacterial attachment and colonization in pig small intestines and to neutralize enterotoxin enterotoxicity would be effective for PWD. Structure-based multiepitope-fusion-antigen (MEFA) technology using a backbone immunogen to present neutralizing epitopes of representing virulence factors capacitates development of broadly protective ETEC vaccines. Neutralizing epitopes have been identified from K88 fimbrial adhesin (FaeG) and enterotoxins but not F18 fimbrial adhesin. In this study, we in silico identified immunodominant epitopes from F18ac fimbrial subunit FedF which plays a critical role in F18 fimbrial adherence, genetically fused each epitope to a carrier, examined immunogenicity of each epitope fusion, and determined epitope-derived antibodies neutralizing activities against F18 fimbrial adherence. Data showed that seven immune-dominant epitopes were identified from FedF subunit. Fused to heterologous human ETEC adhesin subunit CfaB, epitope fusions induced anti-F18 antibodies in subcutaneously immunized mice. Moreover, antibodies derived from each fusion significantly blocked adherence of a F18-fimbrial E. coli bacteria to pig intestinal cell line IPEC-J2. While all seven epitopes exhibited neutralizing activity, results from this study identified FedF epitopes #3 (IPSSSGTLTCQAGT) and #7 (QPDATGSWYD) the most effective for antibodies against F18 fimbrial adherence, and suggested their future application in PWD vaccine development.

Animal Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is the most common cause of E. coli diarrhea in farm animals. ETEC are characterized by the ability to produce two types of virulence factors: adhesins that promote binding to specific enterocyte receptors for intestinal colonization and enterotoxins responsible for fluid secretion. The best-characterized adhesins are expressed in the context of fimbriae, such as the F4 (also designated K88), F5 (K99), F6 (987P), F17, and F18 fimbriae. Once established in the animal small intestine, ETEC produce enterotoxin(s) that lead to diarrhea. The enterotoxins belong to two major classes: heat-labile toxins that consist of one active and five binding subunits (LT), and heat-stable toxins that are small polypeptides (STa, STb, and EAST1). This review describes the disease and pathogenesis of animal ETEC, the corresponding virulence genes and protein products of these bacteria, their regulation and targets in animal hosts, as well as mechanisms of action. Furthermore, vaccines, inhibitors, probiotics, and the identification of potential new targets by genomics are presented in the context of animal ETEC.

CD14 in the TLRs signaling pathway is associated with the resistance to E. coli F18 in Chinese domestic weaned piglets

Escherichia coli F18 (E. coli F18) is mainly responsible for post-weaning diarrhea (PWD) in piglets. The genetic basis and regulatory mechanism of E. coli F18 resistance in Chinese domestic weaned piglets remain unclear. Meishan piglets were used as model animals to test their susceptibility to E. coli F18. By performing a comparative transcriptome study on duodenum tissues of sensitive and resistant pigs, we identified 198 differentially expressed genes (DEGs; 125 upregulated and 73 downregulated) in the resistant pigs. DEGs were predominately involved in immune system pathways, including the Toll-like receptor (TLR) signaling pathway. qPCR and western blot showed CD14, IFN-α, TLR4 and IL-1β, etc. in the TLR signaling pathway had significantly higher expression levels in lipopolysaccharide (LPS)-induced small intestinal epithelial cell lines (IPEC-J2) than those in normal IPEC-J2 cells. Immunohistochemical analysis showed the increased expression of CD14 gene in the E. coli F18-resistant individuals. After CD14 knockdown, the levels of cytokines IL-6 and IL-12 were significantly reduced in IPEC-J2 cell supernatants. The adhesion ability of F18ab strain with IPEC-J2 cells was significantly increased (p < 0.01). This study revealed the TLR signaling pathway, and especially CD14, probably plays an important role in resistance to E. coli F18 infection in Chinese domestic piglets.

Adhesins of Enterotoxigenic Escherichia coli Strains That Infect Animals

The first described adhesive antigen of Escherichia coli strains isolated from animals was the K88 antigen, expressed by strains from diarrheic pigs. The K88 antigen was visible by electron microscopy as a surface-exposed filament that was thin and flexible and had hemagglutinating properties. Many different fimbriae have been identified in animal enterotoxigenic E. coli (ETEC) and have been discussed in this article. The role of these fimbriae in the pathogenesis of ETEC has been best studied with K88, K99, 987P, and F41. Each fimbrial type carries at least one adhesive moiety that is specific for a certain host receptor, determining host species, age, and tissue specificities. ETEC are the most frequently diagnosed pathogens among neonatal and post-weaning piglets that die of diarrhea. Immune electron microscopy of animal ETEC fimbriae usually shows that the minor subunits are located at the fimbrial tips and at discrete sites along the fimbrial threads. Since fimbriae most frequently act like lectins by binding to the carbohydrate moieties of glycoproteins or glycolipids, fimbrial receptors have frequently been studied with red blood cells of various animal species. Identification and characterization of the binding moieties of ETEC fimbrial adhesins should be useful for the design of new prophylactic or therapeutic strategies. Some studies describing potential receptor or adhesin analogues that interfere with fimbria-mediated colonization have been described in the article.

Alpha (1,2)-fucosyltransferase M307A polymorphism improves piglet survival

To confirm the beneficial effects of alpha (1,2)-fucosyltransferase (FUT1) M307 (A) on piglet survival on commercial farms, we performed PCR-RFLP analysis of FUT1 M307 in successfully marketed (n = 245) and disease affected/deceased pigs during weaning (n = 252) at a commercial farm. We also evaluated the FUT1 genotypes of 190 healthy pigs from three different genetic backgrounds. The distribution of genotypes differed between the successfully marketed and disease affected/deceased pig groups. The frequency of the A allele, associated with resistance to edema and post-weaning diarrhea, was higher in the post-weaning survival group (0.21) than in the non-survival group (0.16, P < 0.05). The odds ratio for piglet survival between AA and GG genotypes was 1.98; thus, piglet survival for individuals with the AA genotype was almost two-fold greater than for GG individuals. The FUT1 gene polymorphism can be used as an effective marker for selection programs to improve post-weaning piglet survival.

Study on the age-dependent tissue expression of FUT1 gene in porcine and its relationship to E. coli F18 receptor

Escherichia coli (E. coli) that produces adhesin F18 is the main pathogen responsible for porcine post-weaning diarrhea and edema disease. The receptor for E. coli F18 has not been described in pigs, however the alpha (1,2)-fucosyltransferase (FUT1) gene on chromosome 6 has been proposed as a candidate. The objective of this study, therefore, was to investigate the relationship between FUT1 gene expression and E. coli F18 receptor in Sutai pigs of different ages (8-, 18-, 30- and 35-day-old). FUT1 gene expression was detected in 11 pig tissues with the highest level in lung, and expressed consistently at the four time points. In most tissues, FUT1 gene expression levels decreased from days 8 to 18, then continually increased on days 30 and 35, with expression around weaning time higher than that on day 8. Gene ontology and pathway analysis showed that FUT1 was involved in 32 biological processes, mainly those integral to the membrane, or involved in glycosylation, as well as regulation of binding, interestingly participating in three pathways related to glycosphingolipid biosynthesis. From this analysis and the high linkage disequilibrium between the FUT1 gene and the E. coli F18 receptor locus, we can speculate that higher expression of the FUT1 gene in small intestine is beneficial to the formation of receptors to the E. coli F18 strain and is related to the sensitivity to the pathogen.

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.

Investigation of the relationship between SLA-1 and SLA-3 gene expression and susceptibility to Escherichia coli F18 in post-weaning pigs

Porcine post-weaning diarrhea and edema disease are principally caused by Escherichia coli strains that produce F18 adhesin. FUT1 genotyping and receptor binding studies divided piglets into E. coli F18-resistant and -sensitive groups, and the roles of SLA-1 and SLA-3 were investigated. SLA-1 and SLA-3 expression was detected in 11 pig tissues, with higher levels of SLA-1 in lung, immune tissues and gastrointestinal tract, and higher levels of SLA-3 also in lung and lymphoid tissues. Both genes were expressed higher in F18-resistant piglets, and their expression was positively correlated in different tissues; a negative correlation was observed in some tissues of F18-sensitive group, particularly in lung and lymphatic samples. Gene ontology and pathway analyses showed that SLA-1 and SLA-3 were involved in 37 biological processes, including nine pathways related to immune functions. These observations help to elucidate the relationship between SLA class I genes and E. coli F18-related porcine gastrointestinal tract diseases.

Relationship between the expression level of SLA-DQA and Escherichia coli F18 infection in piglets

The expression of SLA-DQA was assayed by Real-time PCR to analyze the differential expression between ETEC F18-resistant and -sensitive post-weaning piglets, and then to compare the expression levels of SLA-DQA in 11 different tissues from 8-, 18-, 30- and 35-day-old ETEC F18-resistant piglets, which aimed at discussing the role of SLA-DQA in resistance to ETEC F18. The results showed that SLA-DQA is broadly expressed in 11 tissues with the highest expression level in lymph nodes, and a relatively higher expression level in lung, spleen, jejunum, and duodenum. In tissues of lymph node, lung, spleen, jejunum, and duodenum, the mRNA expression of SLA-DQA in resistant individuals was significantly higher than that in sensitive ones (P<0.05). In most tissues, the expression of SLA-DQA increased from 8 to 18 and 30 days (weaning day), and increased persistently to 35 days of post-weaning. Expression levels of SLA-DQA on 35 days in most tissues were significant higher than that on 8, 18 and 30 days (P<0.05). The results demonstrated that the resistance to ETEC F18 in post-weaning piglets is related to up-regulation of mRNA expression of SLA-DQA to a certain extent. The analysis suggested that SLA-DQA may be not the direct immune factor that resisted the Escherichia coli F18, but perhaps enhanced humoral immunity and cell immunity to reduce the transmembrane signal transduction of ETEC F18 bacterial LPS and then led to the resistance to ETEC F18 in piglets.

Detecção de cepas patogênicas pela PCR multiplex e avaliação da sensibilidade a antimicrobianos de Escherichia coli isoladas de leitões diarréicos

Avaliou-se a freqüência dos genes de fímbrias (K88, K99, 987P, F18 e F41) e toxinas (LT, Stb, StaP e Stx2e) de cepas de E. coli isoladas de leitões com diarréia usando a técnica de PCR multiplex com primers específicos para esses genes, e estudou-se o padrão de sensibilidade das cepas patogênicas pelo método de difusão em disco ao florfenicol, ceftiofur sódico, colistina, fosfomicina, neomicina, norfloxacina, sulfa + trimetoprim, doxiciclina, tetraciclina e lincomicina. Foram utilizadas 144 amostras de E.coli isoladas de leitões com diarréia, provenientes de granjas localizadas no estado de Minas Gerais. Dessas, 42 (29,2%) foram positivas para pelo menos um dos fatores de virulência testados. Dentre essas 42 amostras, 23 (54,8%) apresentaram genes de fímbria e toxina, sete (16,6%) apresentaram somente genes de toxinas e 12 (28,6%) amostras somente genes de fímbria. O resultado do teste de sensibilidade aos antimicrobianos demonstrou que o florfenicol (89,5 %) e o ceftiofur sódico (84,2%) foram as drogas de melhor eficácia in vitro sobre cepas de E. coli com fatores de virulência.

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.

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.

Expression of mucin-type glycoprotein K88 receptors strongly correlates with piglet susceptibility to K88(+) enterotoxigenic Escherichia coli, but adhesion of this bacterium to brush borders does not

Three antigenic variants of the K88 fimbrial adhesin exist in nature, K88ab, K88ac, and K88ad. Enterotoxigenic Escherichia coli (ETEC) strains that produce these fimbriae cause life-threatening diarrhea in some but not all young pigs. The susceptibility of pigs to these organisms has been correlated with the adherence of bacteria to isolated enterocyte brush borders. Whether that correlation holds for multiple K88 variants and over a broad genetic base of pigs is unknown and was the impetus for this study. We also desired to examine the correlation of the expression of a porcine intestinal brush border mucin-type glycoprotein (IMTGP) which binds K88ab and K88ac with the susceptibility of piglets to K88(+) ETEC. Of 31 neonatal gnotobiotic pigs inoculated with K88ab+ or K88ac+ ETEC, 13 developed severe diarrhea, became dehydrated, and died or became moribund. Another pig became severely lethargic but not dehydrated. In vitro brush border adherence analysis was not possible for 10 of the severely ill pigs due to colonization by challenge strains. However, of the 17 pigs that did not become severely ill, 8 (47%) had brush borders that supported the adherence of K88ab+ and K88ac+ bacteria in vitro, suggesting a poor correlation between in vitro brush border adherence and piglet susceptibility to K88(+) ETEC. By contrast, the expression of IMTGP was highly correlated with susceptibility to K88(+) ETEC. Of the 12 pigs that produced IMTGP, 11 developed severe diarrhea. The other pig that produced IMTGP became lethargic but not severely diarrheic. Only 2 of 18 pigs that did not produce IMTGP became severely diarrheic. Colonizing bacteria were observed in histologic sections of intestines from all pigs that expressed IMTGP except for the one that did not develop severe diarrhea. However, colonizing bacteria were observed in histologic sections from only one pig that did not produce IMTGP. The bacterial concentration in the jejuna and ilea of pigs expressing IMTGP was significantly greater (P < 0.005) than that in pigs not expressing IMTGP. These observations suggest the IMTGP is a biologically relevant receptor for K88ab+ and K88ac+ E. coli or a correlate for expression for such a receptor.