Development of intestinal antibodies against Escherichia coli antigens in piglets with experimental neonatal E. coli diarrhoea

Effects of feeding different roughage components to sows in gestation on bacteriological and immunological parameters in colostrum and immune response of piglets

In piglet production, Escherichia coli (E. coli) and the presence of lipopolysaccharides (LPS) were considered as predominant causative agents in the aetiology of important diseases of sows and piglets. The aim of the study was to assess the effects of feeding different roughage sources to sows in gestation on the microbiota and endotoxin concentration in colostrum and on the specific immune response of their piglets. In two trial runs, a total of 144 sows were assigned to one of the six dietary treatments: the Control group receiving a concentrate diet and five groups with a restrictive supply of the control diet in combination with straw (S), hay (H), clover grass silage (GS), maize silage (MS) or Jerusalem artichoke (JA). During lactation no roughage was offered. Colostrum samples were analysed for bacteriological and immunological parameters. Blood samples were taken from two piglets per corresponding litter to examine the concentration of C-reactive protein (CRP) and of specific antibodies to LPS of E. coli (strain J5). Roughage feeding had an effect neither on the total bacterial count nor on the content of E. coli in colostrum of sows. The concentration of LPS in colostrum was reduced in Group MS. The concentration of CRP in the colostrum samples was low and independent of the feeding regime (max. 9.3 µg/ml). However, the administration of roughage components rich in crude fibre (Groups H and S) decreased the level of CRP in colostrum significantly. The analysis of the specific immunoglobulin to LPS of E. coli (strain J5) showed a higher concentration of IgG-anti-LPS in blood serum of piglets from sows of Group JA. The results suggest that the inclusion of selected roughage components may have the potential to affect the immunocompetence of sows and their corresponding piglets.

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.

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.

In vivo emergence of enterotoxigenic Escherichia coli variants lacking genes for K99 fimbriae and heat-stable enterotoxin

Neonatal pigs were inoculated with porcine enterotoxigenic Escherichia coli 431, which carries genes for K99 fimbriae and STaP enterotoxin. Colonies of strain 431 were recovered from feces of pigs for up to 17 days after inoculation and tested for hybridization with gene probes for K99 and STaP. Variants of strain 431 that did not hybridize with the probes were considered to have lost the genes. Variants were recovered from 10 of 13 suckling pigs that survived the infection. Only 0.4% of the isolates recovered during the first 2 days after inoculation were variants. Of the isolates recovered 3 to 5 days after inoculation, 20 to 36% were variants. Variant colonies were detected more frequently among pigs in some litters than in others. The litter with the highest number of variant-shedding pigs had the dam with the highest titer of K99 antibody in her colostrum. Variants also occurred in colostrum-deprived, artificially reared pigs. However, the number of variants detected was lower and they occurred later in the course of the infection in colostrum-deprived pigs than in suckling pigs. More variants were detected and they were detected earlier in colostrum-deprived pigs fed anti-K99 monoclonal antibody than in controls fed anti-K88 monoclonal antibody. Loss of STaP appeared to be secondary to loss of K99 in that some variants lacked only K99 (K99- STaP+) and some lacked both genes (K99- STaP-), but none was of the K99+ STaP- type. Our results confirmed reports of gene loss from enterotoxigenic E. coli during infection. They are consistent with the hypothesis that variants emerge under in vivo selection pressure of K99 antibody and with the speculation that gene loss may be an important component of protection in vaccinated populations. However, the emergence of variants did not appear to play a major role in the recovery of individual pigs from clinical disease.