Effectiveness of vaccination in controlling ovine footrot.
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Efficacy of reducing footrot by use of a commercial vaccine was evaluated over 2 yr with 223 ewes from five crossbred genotypes. Ewes were assigned randomly within genotype, age and initial footrot status to a 2 x 3 factorial array of vaccination in the 1st yr and fall vaccination, winter vaccination or control in the 2nd yr. The flock contained a single Bacteroides nodosus serotype (XV) known to be highly cross-reactive with one of the vaccine serotypes (British serotype H). Vaccination reduced footrot incidence by 61% (P less than .01) in the 1st yr and by 45% (P less than .01) in the 2nd yr. Vaccination of previously uninfected ewes did not significantly reduce the rate of new infection, but vaccination of infected ewes reduced re-infection by 92% (P less than .01). Vaccination in the 1st yr failed to produce any carryover or additive protection in the 2nd yr. Genotypes differed in both footrot incidence (P less than .05) and footrot reduction following vaccination (P less than .05), but the effect was inconsistent between years. Vaccination increased serum antibody titers in both years (P less than .01). Among vaccinates in the 1st yr, infected ewes had lower titer levels than uninfected ewes (P less than .01), but no correlation between titer level and incidence was observed in the 2nd yr. (+info)
Expression of the pilin gene from Bacteroides nodosus in Escherichia coli.
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Bacterial plasmids that direct the expression in Escherichia coli of the pilin of Bacteroides nodosus were constructed. The quantity of pilin produced was greater than that of the pilin synthesized by B. nodosus, but no surface structural pili were present; pilin was found associated with the inner membrane of E. coli. Vaccination of sheep with E. coli containing pilin elicited increases in agglutinating and enzyme-linked immunosorbent assay antibody titers, which in turn were lower than the titers in sheep immunized with pilin from B. nodosus. The E. coli-produced pilin vaccine initially appeared to delay the progression of infection in immunized sheep after a challenge with virulent homologous B. nodosus, but at a later time the severity of foot rot was similar to that in sheep vaccinated with a placebo. (+info)
Expression of pili from Bacteroides nodosus in Pseudomonas aeruginosa.
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The pili of Bacteroides nodosus, the causative agent of ovine footrot, constitute the major host-protective immunogen against homologous serotypic challenge. The pilin gene from B. nodosus 198 has been cloned and morphologically expressed as extracellular pili in Pseudomonas aeruginosa by using a plasmid-borne, thermoregulated expression system. B. nodosus pilin could not be detected in cultures of P. aeruginosa grown at 32 degrees C, but after induction at 37 degrees C, B. nodosus pili were expressed on the cell surface of P. aeruginosa to the virtual exclusion of the host cell pili. Pili harvested from induced P. aeruginosa cultures were used to immunize sheep against footrot. The serum agglutinating antibody titers of vaccinated sheep were comparable to those of sheep receiving pili from B. nodosus. Subsequent challenge of the sheep with B. nodosus 198 indicated that the recombinant- DNA-derived pili vaccine and the B. nodosus pili vaccine provided similar levels of protection against footrot. (+info)
Surface structure of Bacteroides nodosus in relation to virulence and immunoprotection in sheep.
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A comparative electron microscopic study was made of virulent ovine strains, benign ovine strains, bovine strains and culture variants of Bacteroides nodosus using negative staining, thin section and freeze-fracture etch techniques. The plasma membrane, peptidoglycan layer and outer membrane structures were similar in all the organisms, but there were marked differences in the presence of pili, diffuse polar material and additional layer. The variations in these surface structures were examined in relation to the virulence and immunoprotection of B. nodosus towards foot-rot in sheep. Only organisms with abundant pili caused virulent foot-rot; diffuse polar material and perhaps the additional layer may also be associated with virulence, but conclusive evidence was lacking. It appeared that pili and one or more unknown cell components, possibly diffuse polar material but not the additional layer, were necessary for immunoprotection. (+info)
Isolation of the gene encoding pilin of Bacteroides nodosus (strain 198), the causal organism of ovine footrot.
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The gene for pilin, the monomeric protein subunit from which the pilus of Bacteroides nodosus is constructed, has been isolated. Isolation was achieved by cloning the fragmented genome of B. nodosus in Escherichia coli RR1 using the plasmid vector pBR322. Pilin-producing colonies were identified by screening with a colony immunoassay using antiserum from a sheep immunized against purified pili from B. nodosus strain 198, and were further characterized by immunoblot analysis. Final confirmation of the presence of the pilin gene was by nucleotide sequence data which translated to the known pilin amino acid sequence. (+info)
Proteinase isoenzyme patterns of Bacteroides nodosus: distinction between ovine virulent isolates, ovine benign isolates and bovine isolates.
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Bacteroides nodosus isolates from ovine virulent footrot and ovine benign footrot and bovine isolates of low virulence for sheep were distinguishable from each other by their proteinase isoenzyme patterns after polyacrylamide gel electrophoresis. Variants of low virulence were not always distinguishable from their virulent parent strains. The molecular weights of the isoenzymes ranged from 70000 to 129000. The relationship of isoenzyme patterns to virulence is discussed. (+info)
Differentiation of Bacteroides nodosus biotypes and colony variants in relation to their virulence and immunoprotective properties in sheep.
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To obtain a wider definition of variation in the virulence of Bacteroides nodosus and in the protective potency of B. nodosus vaccines, we made a comparison of the in vitro characteristics of isolates from clinical infections of sheep and cattle and of certain colony variants observed previously. Three basic colony types were distinguished: papillate or beaded (B)-type colonies were produced by fresh isolates from advanced ovine foot rot; mucoid (M)-type colonies were formed by isolates from noninvasive B. nodosus infections of the interdigital skin of sheep and cattle, and also by cultures of some primary B-type colonies passaged nonselectively in vitro; and circular (C)-type colonies were formed by B. nodosus that eventually predominated in repeatedly passaged liquid subcultures. Each type could be maintained by selective agar subculturing; one strain was thus passaged 40 times as the B-type colony, at which point the organisms induced severe foot rot in experimentally infected sheep. Cultures of M-type colonies were uniformly less pathogenic and those of C-type colony organisms were avirulent. In vitro changes from prototype B-type colonies to M- and C-variants were nonreversible in these experiments, were accelerated in liquid cultures, and wee accompanied by a diminution in elastase activity of the organisms and in their immunoprotective properties against homologous challenge. Strains differed in their stability to these changes; therefore the choice of an appropriate strain and colony type may be an important consideration in studies of B. nodosus virulence and in the development of effective vaccines. (+info)
Serotypic and biochemical characterization of Bacteroides nodosus isolates from Oregon.
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Ninety-seven Bacteroides nodosus isolates were characterized by the tube agglutination test. Fourteen serotypes were identified including isolates that were serologically similar to Australian serotypes A, B and C. One additional isolate remains untyped and possibly represents another serotype. The isolates were cultured from 20 different flocks. Multiple isolates were obtained from 15 of the flocks and 13 of these had two to seven different B. nodosus serotypes. Eleven B. nodosus isolates representing one Australian and ten Oregon serotypes were nonfermentative in various carbohydrates and did not produce indole. These isolates all exhibited proteolytic activity. The prototype strains of 12 of the 14 serotypes demonstrated virulence as assessed by an elastase production assay. (+info)