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Use of Brucella canis antigen for detection of ovine serum antibodies against Brucella ovis.

Brucella ovis causes a genital disease of sheep manifested by epididymitis in rams and placentitis in ewes producing reduced fertility in the flock. Clinical diagnosis is not sensitive enough and bacteriological testing is not feasible for detection of the disease in large numbers of animals. Indirect methods of serological testing are preferred for routine diagnosis, of which agar gel immunodiffusion (AGID), complement fixation (CF) and ELISA tests are recommended as the most efficient. Since B. ovis shares antigenic components with Brucella canis, it would seem that either strain could be used as antigen with the same results; however, the advantage of the B. canis (M-) strain variant is that it can be used to develop a satisfactory antigen for agglutination tests. We present data on AGID and IELISA tests using B. ovis antigen and rapid screening agglutination test (RSAT), 2-mercapto-ethanol RSAT (2ME-RSAT) and IELISA using B. canis antigen. We tested 225 animals. The cut-off values were adjusted by ROC analysis using 51 negative and 32 positive sera; the IELISA-B. canis cut-off value was 39 (%P) and IELISA-B. ovis, 51 (%P), with 100% sensitivity and specificity. Of the 32 positive sera from the infected flock RSAT detected 32 (100%), 2ME-RSAT 29 (91%) and AGID 31 (97%). Of the 142 sera from suspicious flocks, 46 were negative and 56 positive in all the tests; 16 were positive by RSAT, IELISA-B. canis and IELISA-B. ovis, 20 positive only with RSAT and 2 positive only by both IELISAs. RSAT is a very sensitive screening test that, because of its simplicity and easy interpretation, following a study in larger sample, could replace AGID as a screening test for diagnosis of ovine brucellosis caused by B. ovis. The IELISA-B. canis or IELISA-B. ovis could be used as confirmatory tests, since they show equal specificity and sensitivity.

Agglutination Tests↗

Outer-membrane protein- and rough lipopolysaccharide-specific monoclonal antibodies protect mice against Brucella ovis.

Brucella ovis, a naturally virulent rough Brucella species, is the aetiological agent of ram epididymitis. The identification of protective antigens is necessary to obtain a safe, specific subcellular vaccine. Monoclonal antibodies (MAbs) directed at both brucella outer-membrane proteins (OMPs) and rough lipopolysaccharide (R-LPS) in a mouse protection test were used to identify potential targets for humoral immunity. Mixtures of MAbs directed at the 16.5-, 25-27-, 31-34- and 36-38-kDa OMPs conferred significant protection 7 days after challenge with reference strain B. ovis 63/290 compared with controls receiving either saline or an anti-brucella O-polysaccharide MAb. Furthermore, an anti-R-LPS MAb tested alone conferred protection at a level comparable with that obtained with the mixture of anti-OMP MAbs. The combination of protective OMP MAbs with the anti-R-LPS MAb was also strongly protective. One combination of OMP MAbs, which bound intensely to B. ovis in vitro, was ineffective. These results indicate that B. ovis OMPs and R-LPS are targets for protective antibodies and that they can be regarded as candidates for ram epididymitis subcellular vaccines.

Animals↗

Immunochemical studies of oligosaccharides obtained from the lipopolysaccharide of Brucella ovis.

Brucella ovis rough lipopolysaccharide (R-LPS) was studied with respect to its heterogeneity, chain length, sugar composition and immunological activity. R-LPS was mildly hydrolysed and oligosaccharides were recovered in the upper phase after partition with chloroform-methanol. Gel-filtration of the upper phase in a column of Bio-Gel P-2 yielded oligosaccharides of 2, 4, 6 and 7 monosaccharide units, 2-keto-deoxy-octulosonic acid (KDO), and monosaccharides. Strong acid hydrolysis followed by paper chromatography showed that the hexa- and heptasaccharides are both composed of glucose, KDO and an unidentified sugar while tetrasaccharide is composed of glucose, mannose and glucosamine. These three oligosaccharides were able to inhibit the LPS-antibody reaction in a solid phase radioimmunoassay, suggesting the oligosaccharides bear antigenic determinants of LPS.

Animals↗

Differentiation of Brucella ovis from Brucella abortus by gas-liquid chromatographic analysis of cellular fatty acids.

The cellular fatty acid composition of Brucella ovis and Brucella abortus strains was determined by gas-liquid chromatography. Both species were characterized by the presence of fatty acids 16:0, 17:0, 17:0 cyclopropane, 18:0, 18:1, and 19:0 cyclopropane; B. ovis also contained some 15:0. There were differences in the relative proportions of the fatty acids present, and it was possible to differentiate B. ovis from B. abortus on the basis of the absence of 15:0, lower concentrations of 17:0 and 18:1, and higher concentrations of 19:0 cyclopropane in B. abortus. The data indicate that analysis of cellular fatty acid composition by gas-liquid chromatography can be used for the identification of B. ovis and its differentiation from B. abortus.

Brucella↗

Comparative analyses of proteins extracted by hot saline or released spontaneously into outer membrane blebs from field strains of Brucella ovis and Brucella melitensis.

Sheep infected with Brucella ovis produce antibody responses to the rough lipopolysaccharide and to proteins present in hot saline (HS) extracts of B. ovis (J. I. Riezu-Boj, I. Moriyón, J. M. Blasco, C. M. Marín, and R. Díaz, J. Clin. Microbiol. 23:938-942, 1986). The distribution and antigenic relatedness of proteins in HS extracts and in outer membrane blebs were established by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting for 41 strains of B. ovis and 26 strains of Brucella melitensis of diverse geographic origin. Five major groups of proteins were identified in HS extracts of B. ovis that had been freed of rough lipopolysaccharide: proteins of 43 kilodaltons (kDa), group A (25.5 to 32.0 kDa), group B (21.5 to 22.5 kDa); group C (18.0 to 19.5 kDa), and group D (13.0 to 15.5 kDa). Group A, B, C, and D proteins were also present in blebs. The profiles of proteins in HS extracts or blebs from strains of both Brucella species were very similar. Cross-reactions were demonstrated among HS extracts and blebs of all strains tested in immunoblots performed with an antiserum against the HS extract of a reference strain of B. ovis. Evidence was also provided of an antigenic relationship between group 3 proteins of the outer membrane and some of the proteins in groups A, B, and C. The conservation of these antigens and their immunogenicity in infected animals provide promise that they may serve as components of an effective subcellular vaccine for ovine brucellosis.

Animals↗

Antigenic relationship of Brucella ovis and Brucella melitensis.

Immune sera were prepared in rabbits by the injection of living and acetone-killed cells of Brucella ovis and smooth and rough B. melitensis. The use of whole-cell antigens in agglutination and agglutinin-absorption tests revealed little relationship between B. ovis and smooth B. melitensis, although there was extensive cross-agglutination between B. ovis and rough B. melitensis. The use of water-soluble antigens prepared from ultrasonically treated cells of the three strains revealed extensive cross-reactions in indirect hemagglutination, agar gel precipitation, and immunoelectrophoresis tests, as well as in allergic skin tests in rabbits. The most definitive results were obtained with the immunoelectrophoresis technique. B. ovis antigen produced at least 11 lines with its homologous serum. All were removed by absorption of the serum with rough B. melitensis antigen. All but three were removed by absorption with smooth B. melitensis antigen. Smooth B. melitensis antigen produced 11 lines with its homologous serum, and all but 3 were removed by absorption with B. ovis antigen. Rough B. melitensis produced nine lines with its homologous serum, and eight were removed by B. ovis antigen. The extensive cross-reactions between soluble antigens of B. ovis and B. melitensis are added evidence that B. ovis belongs in the genus Brucella.

Animals↗

Differentiation of Brucella abortus bv. 1, 2, and 4, Brucella melitensis, Brucella ovis, and Brucella suis bv. 1 by PCR.

Several PCR assays which identify the genus Brucella but do not discriminate among species have been reported. We describe a PCR assay that comprises five oligonucleotide primers which can identify selected biovars of four species of Brucella. Individual biovars within a species are not differentiated. The assay can identify three biovars (1, 2, and 4) of B. abortus, all three biovars of B. melitensis, biovar 1 of B. suis, and all B. ovis biovars. These biovars include all of the Brucella species typically isolated from cattle in the United States, a goal of the present research. The assay exploits the polymorphism arising from species-specific localization of the genetic element IS711 in the Brucella chromosome. Identity is determined by the size(s) of the product(s) amplified from primers hybridizing at various distances from the element. The performance of the assay with U.S. field isolates was highly effective. When 107 field isolates were screened by the described method, there was 100% agreement with the identifications made by conventional methods. Six closely related bacteria (Agrobacterium radiobacter, Agrobacterium rhizogenes, Ochrobactrum anthropi, Rhizobium leguminosarum, Rhizobium meliloti, and Rhodospirillum rubrum) and two control bacteria (Bordetella bronchiseptica and Escherichia coli) tested negative by the assay.

Base Sequence↗

Experimental Brucella ovis infection in mouflon (Ovis musimon).

Brucella ovis was isolated for the first time in Italy in 1994 from the genital organs of two domestic rams. In subsequent years bacteriologic and serologic investigations demonstrated an increasing distribution of this disease in domestic sheep. Mouflon (Ovis musimon) occur in several hilly and mountainous areas of Italy where they can potentially contact domestic sheep. To determine if this species may have a role in the epidemiology of B. ovis, four male and four female mouflon, serologically negative for B. ovis and other Brucella spp., were infected intra-conjunctivally with B. ovis strain BG1/94. Physical examinations, including collection of blood samples for serology and bacteriology, were performed weekly. The animals were euthanized 8 mo postinoculation (p.i.). Samples of retropharyngeal, parotid, and iliac lymph nodes; bone marrow; kidneys; spleen; epididymis; testicle; bulbourethral glands; seminal vesicles; uterus; and oviducts were collected from each animal as appropriate for histopathology and bacteriology. At the time of euthanasia none of the animals exhibited obvious clinical signs of brucellosis. The animals seroconverted 2 wk p.i. and became seronegative 24 wk p.i. Bacterial cultures, including hemocultures, were negative. No lesions due to B. ovis infection were revealed by histologic examinations. Brucella ovis probably did not infect mouflon and this wild sheep is not likely to play a role in the epidemiology of contagious epididymitis caused by B. ovis.

Animals↗

Restriction endonuclease analysis of Brucella ovis and other Brucella species.

Brucella ovis DNA was analysed by using 11 different restriction endonucleases. The most clearly resolved DNA fragment patterns were obtained after digestion with the enzyme Hind III. When DNA preparations from 35 strains of B. ovis were digested with this enzyme, the fragment patterns appeared to be identical. The patterns obtained after Hind III digestion of DNA from one strain each of B. abortus, B. canis and B. melitensis were more similar to each other than to the B. ovis pattern.

Animals↗

Studies of antigens for complement fixation and gel diffusion tests in the diagnosis of infections caused by Brucella ovis and other Brucella.

Sonically treated and saline-extracted antigens of Brucella ovis, B. canis, B. abortus, and B. melitensis were compared in gel diffusion, complement fixation, and serum absorption tests. All the sonically extracted antigens showed cross-reactions with sera from animals infected or immunized with these species, whereas the saline-extracted antigens were specific for the surface of the rough or smooth colonial phase of the species or strain. The saline-extracted antigens of B. ovis and B. melitensis were both eluted as a single peak in the void volume by Sephadex G-200 column chromatography, in gel diffusion had staining characteristics of lipoproteins, but in immunoelectrophoresis showed distinct mobility patterns. Serological activity for both gel diffusion and complement fixation tests was demonstrated in the immunoglobulin G-containing fraction of sera taken from sheep 12 to 412 days after infection with B. ovis. The gel diffusion test with saline extract of B. ovis is as sensitive as the complement fixation test for the diagnosis of ram epididymitis and is more practical.

Absorption↗

Comparison of lipopolysaccharide and outer membrane protein-lipopolysaccharide extracts in an enzyme-linked immunosorbent assay for the diagnosis of Brucella ovis infection.

Brucella ovis hot saline extracts and petroleum ether-chloroform-phenol lipopolysaccharide were compared in an enzyme-linked immunosorbent assay for the diagnosis of B. ovis ram epididymitis. Hot saline extracts detected greater numbers of infected rams. Chemical characterization of the antigens showed that, although both contained lipopolysaccharide, hot saline extracts also contained outer membrane proteins. These proteins were active as antigens in Western blot tests with sera of infected rams, and therefore they explained the better diagnostic results obtained with hot saline extracts. However, compared with lipopolysaccharide, hot saline extracts showed a higher degree of cross-reactivity with sera from smooth B. melitensis-infected animals. This observation might be explained by the presence of B. ovis outer membrane proteins in hot saline extracts which lack the specificity necessary for serological identification of the Brucella species present.

Animals↗

Serological comparison between Histophilus ovis, Actinobacillus seminis and Brucella ovis.

The serological relationships between 4 strains of Histophilus ovis, the neotype strain of Actinobacillus seminis and Brucella ovis were examined using a cross-absorption complement-fixation technique. It was found that the 4 strains of H. ovis were serologically homologous and that an incomplete relationship existed between these organisms and A. seminis. Anteriserums prepared against one strain of H. ovis and the strain of A. seminis gave a weak, apparently non-specific cross-reaction with Br. ovis antigen. The practical significance of these results is discussed.

Actinobacillus↗

Antimicrobial therapy for rams with Brucella ovis infection of the urogenital tract.

Rams shedding Brucella ovis in semen but without palpable abnormalities of the epididymides were treated with long-acting oxytetracycline for 15 days and dihydrostreptomycin for 7 days (n = 9) or conventional oxytetracycline and dihydrostreptomycin (n = 9) for 7 days. Nine rams were not treated. More treated rams were considered to have satisfactory breeding soundness examination results at posttreatment weeks 3, 7, 12, and 19. Nontreated rams continued to shed B ovis in semen. After treatment, B ovis was not recovered from 78% of rams given long-acting oxytetracycline and dihydrostreptomycin or from 89% of rams given conventional oxytetracycline and dihydrostreptomycin. At week 21, all rams were euthanatized, and specimens of the testes and epididymides were bacteriologically cultured for B ovis. Brucella ovis was not recovered from the testes of rams or from the epididymides from rams not shedding the organism in the semen. In one treated ram, B ovis was recovered from the semen but not from other tissues. All rams remained ELISA-positive, with the exception of 2 treated rams that ceased shedding B ovis in semen immediately after treatment was started; both these rams became ELISA-negative on the last examination at week 19.

Animals↗

Nucleotide sequence and expression of the gene encoding the major 25-kilodalton outer membrane protein of Brucella ovis: Evidence for antigenic shift, compared with other Brucella species, due to a deletion in the gene.

The nucleotide sequences encoding the major 25-kDa outer membrane protein (OMP) (omp25 genes) of Brucella ovis 63/290, Brucella melitensis 16M, Brucella suis 1330, Brucella canis RM6/66, and Brucella neotomae 5K33 (all reference strains) were determined and compared with that of Brucella abortus 544 (P. de Wergifosse, P. Lintermans, J. N. Limet, and A. Cloeckaert, J. Bacteriol. 177:1911-1914, 1995). The major difference found was between the omp25 gene of B. ovis and those of the other Brucella species; the B. ovis gene had a 36-bp deletion located at the 3' end of the gene. The corresponding regions of other Brucella species contain two 8-bp direct repeats and two 4-bp inverted repeats, which could have been involved in the genesis of the deletion. The mechanism responsible for the genesis of the deletion appears to be related to the "slipped mispairing" mechanism described in the literature. Expression of the 25-kDa outer membrane protein (Omp25) in Brucella spp. or expression from the cloned omp25 gene in Escherichia coli cells was studied with a panel of anti-Omp25 monoclonal antibodies (MAbs). As shown by enzyme-linked immunosorbent assay (ELISA) and immunoelectron microscopy, Omp25 was exported to the outer membrane in E. coli expressing either the truncated omp25 gene of B. ovis or the entire omp25 genes of the other Brucella species. Size and antigenic shifts due to the 36-bp deletion were demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting and by the differences in binding patterns in ELISA of the anti-Omp25 MAbs at the cell surface of E. coli cells harboring the appropriate gene and of cells of B. ovis and other Brucella species. In particular, MAbs directed against discontinuous epitopes of the entire Omp25 showed the absence of, or a significant reduction in, antibody reactivity with the B. ovis truncated Omp25. The results indicated that, as defined by the MAbs, exported Omp25 probably presents similar topologies in the outer membranes of E. coli and Brucella spp. and that the short deletion found in the omp25 gene of B. ovis has important consequences for the expression of surface B-cell epitopes which should be considered for the development of vaccines against B. ovis infection.

Amino Acid Sequence↗