Cloning of Brucella abortus gene and characterization of expressed 26-kilodalton periplasmic protein: potential use for diagnosis

Brucella spp. are the causative agents of brucellosis in many different hosts, including humans. Most of the serological methods of diagnosis are based on the detection of antilipopolysaccharide antibodies, which makes the differentiation of vaccinated animals from infected animals difficult. By using molecular biology techniques, a gene that encodes a 26-kDa protein (BP26) was isolated from a Brucella abortus S19 genome lambda gt11 library. This protein is in the periplasm of B. abortus and in transformed Escherichia coli. It is exported to the periplasm via a preprotein of 29 kDa with a signal sequence of 28 amino acids. The nucleotide and amino acid sequences of this gene and protein did not show any similarity with those of previously sequenced genes. The use of this protein in Western blotting allowed the differentiation between vaccinated bovines from infected bovines and the detection of infected rams: on the other hand, sera from human patients with active brucellosis were positive, while sera from human patients with chronic brucellosis or without clinical signs were nonreactive. BP26 might be of value as an antigen for serological diagnosis of brucellosis in different mammals.

Serological crossreactivity between Brucella abortus and Yersinia enterocolitica 0:9 II the use of Yersinia outer proteins for the specific detection of Yersinia enterocolitica infections in ruminants

Yersinia outer protein (YOP) preparations from Y. enterocolitica and Y. pseudotuberculosis were used as antigens in immunoblots for the detection of Yersinia infections in experimentally and naturally infected ruminants. Sera from 9 groups of animals were used: (1) 51 sera from cattle which were false-positive in the standard brucellosis serological tests, (2) 52 sera from brucellosis-negative cattle, (3) 51 sera from a deer herd in which 16 animals were positive in the brucellosis tests and Yersina species were isolated from 5 animals, (4) 50 sera from a deer herd in which sera from all animals were negative in the brucellosis tests, (5) 107 sera from brucellosis-negative cattle which were received from throughout New Zealand, (6) 30 sera from cattle naturally infected with B. abortus and from which B. abortus was isolated, (7) 55 sera from cattle naturally infected with B. abortus, (8) 26 sera from cattle experimentally infected with B. abortus, with mostly high titres in the conventional brucellosis tests, and (9) sera taken weekly from 3 cattle experimentally infected with Y. enterocolitica 0:9. In all 3 Y. enterocolitica 0:9 experimentally infected animals the antibody reactivity against major YOPs in the Y. enterocolitica and in the Y. pseudotuberculosis YOP preparation correlated well with the strength in the classical brucellosis tests and with the staining of smooth lipopolysaccharides (SLPS) in blots, thus confirming the usefulness of YOPs for the detection of Yersinia infections. Sera from naturally infected cattle and deer herds, regardless of whether they were false positive or negative in the brucellosis tests, showed high frequencies of staining in YOP blots (53-58% in cattle and 80-100% in deer), indicating a high prevalence of field infections with Yersinia species in New Zealand. In two of the three sera groups from B. abortus infected animals, antibodies against YOPs were detected with high frequency, showing that dual infections may be common and may interfere with differential serological testing.

Morphometric analysis of CD4+, CD8+, and gamma/delta+ T-lymphocytes in lymph nodes of cattle vaccinated with Brucella abortus strains RB51 and 19

T-lymphocyte subpopulations were examined in vivo by computer-assisted morphometry of superficial cervical lymph nodes of cattle vaccinated with Brucella abortus. Twenty-four 8-month-old Hereford heifers were injected subcutaneously in the axillary area with 1 x 10(10) live B. abortus strain RB51 (SRB51, n = 12) or strain 19 (S19, n = 6) suspended in 2 ml of saline. Six control heifers were injected with sterile saline. Lymph nodes were collected at 1, 2, 4, 6, 10 and 12 weeks postvaccination. Both SRB51 and S19 were cultured from lymph nodes, but SRB51 persisted for a longer period after vaccination (10 weeks) than S19 (6 weeks). Cryostat sections were incubated with monoclonal antibody to CD4 (IL-A11), CD8 (IL-A51), or gamma/delta (IL-A29) bovine T-cell surface antigen and processed for immunoperoxidase staining. Numbers of stained lymphocytes in randomly selected fields were calculated using image-analysis software. There were no significant differences in the number (P = 0.07) or relative proportions (P = 0.22) of CD4+, CD8+, and gamma/delta+ lymphocytes in SRB51, S19, and control lymph nodes. There was a statistically significant difference in the distribution of the three T-cell subsets (P = 0.001). The CD4+ cells were most closely grouped and the gamma/delta+ cells had the most widely scattered distribution, regardless of vaccination status. The results support other studies indicating lymphocyte depletion is not a sequela of infection with B. abortus vaccine strains given to conventionally reared cattle.

Evaluation of PCR and indirect enzyme-linked immunosorbent assay on milk samples for diagnosis of brucellosis in dairy cattle

A study was performed to evaluate the previously described PCR (C. Romero, C. Gamazo, M. Pardo, and I. López-Goñi, J. Clin. Microbiol. 33:615-617, 1995) for the diagnosis of brucellosis in dairy cattle. Milk samples from 56 Brucella milk culture-positive cattle and from 37 cattle from Brucella-free herds were examined for Brucella DNA by PCR and for specific antibodies by an indirect enzyme-linked immunosorbent assay (ELISA). The specificities of both tests were 100% when testing the milk samples from Brucella-free cattle. The milk samples from 49 infected cattle were positive by PCR (87.5% sensitivity), and 55 were positive by ELISA (98.2% sensitivity). A PCR-positive sample was negative by ELISA, and 7 ELISA-positive samples were PCR negative, yielding an observed proportion of agreement of 0.91 for the two tests. Although the results suggest that ELISA is a better screening test than PCR, the combined sensitivity of the two assays was 100%, and their simultaneous application could be more useful than one test alone for a rapid screening of brucellosis in dairy cattle.

Serological crossreactivity between Brucella abortus and Yersinia enterocolitica 0:9 I immunoblot analysis of the antibody response to Brucella protein antigens in bovine brucellosis

Sera from three groups of Brucella abortus infected cattle were examined in immunoblots with the following antigens: sodium dodecyl sulfate/mercapto ethanol (SDS/ME) extracts of two rought B. abortus strains (45/20 and RB51) and rough B. ovis, smooth lipopolysaccharides (SLPS) from B. abortus strain 99 and Y. enterocolitica 0:9, and a cytoplasmic extract from smooth B. abortus strain 19-S. The sera groups were: (1) 26 sera from animals, experimentally infected with B. abortus strain 544, which were all positive in the conventional brucellosis serological tests; (2) 152 sera from naturally infected cattle herds with varying titres in the conventional brucellosis tests, and (3) 30 sera from naturally infected cattle with varying titres in the conventional brucellosis tests and from which B. abortus was cultured. B. abortus strain 99 and Y. enterocolitica serotype 0:9 SLPS staining showed up frequently in all sera groups and correlated well with the strength in the conventional brucellosis tests, confirming the immunodominance of SLPS in B. abortus infections. Another immunodominant component of 50-80 kDa was found in the rough B. abortus 45/20 antigen preparation but not in the B. abortus RB51 and in the B. ovis cell extracts. This component was also recognised by sera from Y. enterocolitica 0:9 infected cattle and is probably a protein-lipopolysaccharide complex. Although many of the sera from B. abortus infected cattle with high titres in the conventional brucellosis tests showed complex protein staining patterns in blots, no protein bands other than the 50-80 kDa bands were found to be immunodominant.

Serum sensitivity of field isolates and laboratory strains of Brucella abortus

OBJECTIVE

To evaluate the ability of bovine complement to kill a variety of field isolates and laboratory strains of Brucella abortus.

DESIGN

The experimental approach was to determine the sensitivity of B abortus isolates to killing by bovine serum, and to document the role of complement in brucellacidal activity.

SAMPLE POPULATION

Six laboratory isolates and 12 field isolates of B abortus were tested.

PROCEDURE

The ability of B abortus to survive exposure to undiluted bovine serum for 2 hours at 37 C was assessed. The role of complement in killing was determined by examining the ability of heat (56 C for 60 minutes) and cobra venom factor to obliterate the activity in serum, and by detecting binding of the ninth component of bovine complement to serum-sensitive target cells.

RESULTS

Isolates of B abortus that were resistant to the bactericidal activity of normal bovine serum were revealed. These included field isolates and laboratory strains. Furthermore, the study confirmed earlier reports that bovine serum-mediated killing of B abortus is caused by the complement cascade.

CONCLUSIONS

Some isolates of B abortus, like other gram-negative bacteria, were resistant to complement-mediating killing. Resistance was associated with smooth colony morphology. Isolates lacking detectable O antigen were serum sensitive.

Rates of seroconversion in the progeny of Brucella abortus seropositive and seronegative cattle and buffalo

The authors estimated the rates of development of serum antibodies against Brucella abortus, between January 1987 and December 1990, in female Jersey cattle and buffalo weaned from seropositive and seronegative dams, and used logistic regression analysis to examine the epidemiological relationship of these rates with the serum antibody status of dams. The offspring from both seropositive and seronegative dams were reared together in calf pens, while separate pens were used for bovine and buffalo calves. Each of the bovine calves was manually fed two litres of bulked milk (pooled from seronegative and seropositive cows) twice a day, in the morning and evening. The buffalo calves, however, were allowed to suckle their respective dams before and after manual milking of each buffalo, in the morning and evening. Bovine calves and buffalo calves were weaned at approximately six months of age and moved to sheds for young livestock. At maturity, the female offspring were artificially inseminated, and pregnancy was subsequently diagnosed by rectal palpation. The rate of seroconversion in the progeny of seropositive Jersey cattle was 26.4% (14 of 53 animals) compared to 14.3% (11 of 77 animals) in the progeny of seronegative cattle; this difference was non-significant (P = 0.1342). In buffalo, however, the rate of seroconversion in the progeny of seropositive dams (43.3% = 13/30) was significantly higher (P = 0.0002) than in the progeny of seronegative buffalo (8.8% = 6/68). The logistic regression analysis revealed that the progeny of seropositive buffalo were approximately 6.2 times more likely to have developed serum antibodies by the time of first calving than the progeny of seronegative buffalo (adjusted odds ratio [OR]) = 6.2; 95% confidence interval [CI] = 1.5, 36.4). This relationship was non-significant, however, for the progeny of seropositive cattle (adjusted OR = 2.1; 95% CI = 0.6, 7.4). The implications of these results and potential sources of bias are discussed.

Specific bovine brucellosis diagnosis based on in vitro antigen-specific gamma interferon production

In order to improve the specificity of the diagnosis of bovine brucellosis, we developed a test which can be regarded as an in vitro correlate of the delayed-type hypersensitivity test (DTH). A mixture of cytoplasmic proteins from Brucella melitensis B115 was used as a specific antigenic stimulus in bovine whole blood culture. Supernatants harvested at 18 to 24 h after the in vitro antigenic stimulus were assayed for their gamma interferon (IFN-gamma) content by using a commercial sandwich enzyme-linked immunosorbent assay kit. The IFN-gamma assay was evaluated with 10 heifers during the course (80 days) of an experimental infection and with 14 cows from an ongoing brucellosis outbreak. All of these animals were slaughtered, and pertinent organs were subjected to classical bacteriological analyses. In addition, we analyzed 23 field cases in which false-positive serological reactions occurred. The IFN-gamma results were compared with those of the standard DTH and a battery of serological assays, and they were correlated with bacteriological data. Both for the experimental infection and for the field brucellosis outbreak, the IFN-gamma assay detected infection in more animals than any combination of the serological tests, and it detected infection earlier than these tests. Finally, none of the samples from cows showing false-positive serological reactions was classified as positive by the IFN-gamma assay, attesting to its specificity and to its usefulness in interpreting ambiguous serological results. A rapid and convenient alternative to the DTH, the IFN-gamma assay appears to be an ideal method that is complementary to the serological diagnosis protocols.

Comparative analysis of immune responses in cattle vaccinated with Brucella abortus strain 19 or strain RB51

Immune responses were measured for 12 weeks following vaccination of cattle with either Brucella abortus strain (S) 19 or SRB51. Cattle vaccinated with S19, but not with SRB51, produced antibodies that agglutinated B. abortus S1119 in the standard tube agglutination test. Cattle vaccinated with S19 or SRB51 produced antibodies to the surface antigens of SRB51 when measured by a dot enzyme-linked immunosorbent assay. Superficial cervical lymph node (LN) cells obtained by biopsy at 10 and 12 weeks from cattle given the S19 or SRB51 vaccine exhibited similar proliferative responses when incubated in vitro with gamma-irradiated B. abortus S2308. At 10 and 12 weeks after vaccination, LN cells obtained from cattle given S19 or SRB51 proliferated to 22 protein fractions (106-18 kDa proteins) of B. abortus S2308 that were isolated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Twelve of the same 22 fractions, which contained 49-27 kDa proteins, produced a stimulation index of greater than 10 when incubated with LN cells taken from S19-vaccinated or SRB51-vaccinated cattle. Two factions, which contained 27 kDa proteins of S2308, induced the highest proliferative response (stimulation index 25 or greater) by LN cells in cattle given either S19 or SRB51. These results suggest that cattle vaccinated with S19 or SRB51 have similar LN immune responses to S2308, but unlike S19, SRB51 does not induce positive results in the standard tube agglutination test used to diagnose brucellosis in cattle.

The use of divalent cation chelating agents (EDTA/EGTA) to reduce non-specific serum protein interaction in enzyme immunoassay

An indirect enzyme immunoassay (ELISA) for detection of bovine antibody to Brucella abortus was modified by the addition of divalent chelating agents to the serum diluent. This addition resulted in an increase in specificity from 96.0% in the regular assay to 99.4% in the modified procedure. Of the 15,715 sera initially tested by the indirect ELISA, 691 that had given positive reactions were selected for retesting in the indirect ELISA with EDTA/EGTA added. The buffered plate antigen test (BPAT) correctly identified 98.6% of the samples as negative. The addition of chelating agents did not alter the sensitivity of the indirect ELISA, which correctly classified 609 sera from animals from which B. abortus had been isolated as positive. The sensitivity of the BPAT was 97.8%.

Lymphocyte proliferation in response to immunodominant antigens of Brucella abortus 2308 and RB51 in strain 2308-infected cattle

Lymphocyte proliferation in response to proteins from the Brucella abortus strain 2308 (S2308) and the lipopolysaccharide (LPS) O-antigen-deficient mutant of S2308, strain RB51 (SRB51), was measured in S2308-infected cattle following abortion. Supramammary and superficial cervical lymph node lymphocytes from infected cattle proliferated most when incubated with 27- to 18-kDa proteins of S2308 or SRB51. Proteins of SRB51, which contained no LPS O antigens, induced lymphocyte proliferation similar to that induced by S2308 proteins, which contained LPS O antigens. These results indicate that 27- to 18-kDa proteins, but not LPS O antigens, of S2308 and SRB51 are immunodominant in S2308-infected cattle as assessed by lymphocyte proliferation assays.

Improvements to the competitive ELISA for detection of antibodies to Brucella abortus in cattle sera

This paper reports improvements in the competitive ELISA (cELISA) for the detection of serum antibodies to Brucella abortus through modification of the coating of antigen and of the enzyme labelling of the monoclonal antibody conjugate. The covalent linkage of poly-L-lysine to the o-polysaccharide antigen of Brucella abortus enhanced its binding to the polystyrene matrix which resulted in a more efficient and reliable cELISA. Optimal discrimination between vaccinated and infected cattle was achieved by adjustment of the ratio between the monoclonal antibody used in the cELISA and the horseradish peroxidase. Both modifications resulted in a refined, more efficient and reliable cELISA with potential as a routine serodiagnostic assay for Brucellosis.

Serologic responses in diagnostic tests for brucellosis in cattle vaccinated with Brucella abortus 19 or RB51

Serologic responses in the particle concentration fluorescence immunoassay and the card, complement fixation, and tube agglutination tests were measured for 10 weeks after vaccination of cattle with either Brucella abortus 19 or the lipopolysaccharide O-antigen-deficient mutant, strain RB51. The responses of strain 19-vaccinated cattle were positive, whereas those of strain RB51-vaccinated cattle were negative, in all of the tests. These results indicate that cattle vaccinated with strain RB51 fail to produce antibodies that can be detected by conventional serologic tests that are used to diagnose bovine brucellosis.

Comparison of particle concentration fluorescence immunoassay to card and complement fixation tests using isolation of Brucella abortus as the standard

Serologic test data and bacteriologic culture results from 816 cattle were evaluated. Brucella abortus (field strain or strain 19) was isolated from 27.3% of the cows. Results of the card test, particle concentration fluorescence immunoassay (PCFIA), and complement fixation (CF) test were compared. Antibody titers were directly associated with B. abortus isolation, with the majority (64.7%) of field strain isolations having a PCFIA value of < or = 0.300 and a CF test result of at least 1+ at a 1:160 dilution. The specificity of the CF test was significantly higher than that of the PCFIA (at CF > or = 1:40 and PCFIA < or = 0.300).

Isolation of Brucella abortus ssb and uvrA genes from a genomic library by use of lymphocytes as probes

Brucella abortus proteins from virulent S2308 expressed from a pBluescript II SK- genomic library stimulated peripheral blood mononuclear (PBM) cell proliferation from cattle vaccinated with B. abortus S19. The method described here permits a rapid and directed approach to isolate genes encoding antigens of B. abortus that interact with lymphocytes primed to the living bacterium. The supernatants from the bacterial host JM109 (DE3) were cultured with freshly isolated bovine PBM cells. A total of 300 clones were evaluated. Ten clones were identified that stimulated T-lymphocyte proliferation. Among them, one clone with a 2.5-kb insert stimulated T-lymphocyte proliferation in all three animals, suggesting that the proteins encoded by genes within this fragment may represent immunodominant antigens. DNA sequencing of this clone reveals two large open reading frames (ORFs). ORF II has a high degree of similarity to the Escherichia coli ssb gene, which codes for the single-stranded DNA binding protein. ORF I, in the opposite direction to ORF II, shows similarity to the N terminus of the E. coli uvrA gene, which codes for one of the three subunits of the E. coli ABC excision nuclease. The observation that the PBM cells recognized and proliferated in response to proteins expressed from single clones provides a novel strategy to select bacterial antigens that may prove useful in designing alternative vaccines against brucellosis.

A serological survey of bovine brucellosis in the Molopo District of Bophuthatswana

A serological investigation was carried out in the Molopo district of Bophuthatswana to determine the prevalence of brucellosis titre in heifers and cows (n = 9,675) over 24 months of age, which were grazing on communal tribal and privately owned land. The Rose Bengal, micro serum agglutination and complement fixation (CFT) tests were used. Two hundred and two (2.1%) animals tested positive with a CFT titre of 30 (IU ml-1) or higher. Factors that could have contributed to the relatively low prevalence are discussed.

Antibody response to the 89-kDa outer membrane protein of Brucella in bovine brucellosis

The antibody response of cattle to the minor 89-kDa outer-membrane protein (OMP) of brucella was measured by indirect ELISA with the purified protein and compared with the antibody response to smooth lipopolysaccharide (S-LPS). Pre-incubating sera with sonicated cell extracts of Escherichia coli prevented the binding of antibodies from uninfected animals to the 89-kDa OMP, suggesting the presence of one or more cross-reactive epitopes on this protein. In cattle infected experimentally with Brucella abortus, the antibody response to the 89-kDa OMP was later and less intense than that to S-LPS. In naturally infected cattle, 68% of animals showing an antibody response to S-LPS also showed an antibody response to the 89-kDa OMP. Results indicate that specific epitopes of the 89-kDa OMP in combination with those of other OMPs could be useful for diagnosis of brucellosis in cattle.

Immune responses and protection against infection and abortion in cattle experimentally vaccinated with mutant strains of Brucella abortus

Twenty-four 10-month-old Polled Hereford heifers were inoculated SC with live cells of one of the following strains of Brucella abortus: S19 delta 31K (n = 4), S19 delta SOD (n = 4), RB51 (n = 4), and strain 19 (n = 6); controls (n = 6) were given saline solution. Heifers given the deletion mutants S19 delta 31K and S19 delta SOD, and those given strain 19 developed antibody responses to B abortus and cutaneous reactions to brucellin. Heifers given strain RB51 did not develop antibodies that reacted in the standard tube agglutination test, but sera reacted in tests, using an antibody dot-blot assay containing RB51 antigen. The S19 delta 31K and S19 delta SOD strains of B abortus isolated from lymph node tissue after vaccination did not differ genetically from the master stock strain. All heifers were bred naturally at 16 to 17 months of age, and were challenge-exposed intraconjunctivally with virulent B abortus strain 2308 during the fifth month of pregnancy. All vaccinated heifers were protected (ie, none aborted and none had B abortus isolated from their tissues after parturition). Calves born from vaccinated dams were free of B abortus. Antibody responses in heifers after challenge exposure were an indicator of immunity. All 5 control heifers (nonvaccinated) developed serum antibodies after challenge exposure; 3 aborted, and 1 delivered a small, weak calf at 8.5 months of gestation. Thus live mutant strains of B abortus can induce protective immunity when given at 10 months of age, and strain RB51 is a strong candidate for further testing.

Modulation of the intracellular survival of Brucella abortus by tuftsin and muramyl dipeptide

Tuftsin, a physiologic bioactive peptide of animal origin, and muramyl dipeptide, a synthetic bioactive glycopeptide of microbial origin, are known to enhance several recognized macrophage functions and increase non-specific resistance of the host against a number of pathogens. The influence of these two bioactive peptides was studied in permissive bovine mammary macrophages that were unable to control the intracellular replication of Brucella abortus and restrictive bovine mammary macrophages that were able to effectively reduce the intracellular survival of B. abortus. Addition of tuftsin (Thr-Lys-Pro-Arg) or muramyl dipeptide significantly (P < 0.03) enhanced the ability of the permissive macrophages to control the intracellular replication of B. abortus strain 2308 and resulted in the functional conversion of the permissive macrophages into restrictive macrophages. Addition of tripeptide tuftsin fragment (Lys-Pro-Arg), a natural inhibitor of tuftsin, to the medium completely abrogated the effect of tuftsin (P < 0.03). No additive effect on the ability of the macrophages to control the survival of B. abortus resulted from the combination of tuftsin and muramyl dipeptide.

Comparison of Brucella abortus antigen preparations for in vitro stimulation of immune bovine T-lymphocyte cell lines

Three Brucella abortus antigen preparations were tested for stimulatory activity with immune bovine T-lymphocyte cell lines in vitro. A total of 32 polyclonal T-lymphocyte cell lines were derived from two steers each from four immunization groups: (1) B. abortus Strain 19 (S19) alone, (2) heat-killed B. abortus whole bacterial cells (HKC) alone, (3) S19 with recombinant human interleukin 2 (rHuIL-2), (4) HKC with rHuIL-2. Peripheral blood mononuclear cells were isolated at 2 and 9 weeks post immunization and cultured in vitro with either HKC antigen or B. abortus soluble antigen (BASA) with recombinant bovine interleukin 2 (rBoIL-2) to initiate four cell lines per steer. Sixteen of the resulting T-lymphocyte cell lines (from the S19 and S19+IL-2 groups) were tested through indirect immunofluorescence for expression of cell surface markers CD2, CD4, CD6, CD8, major histocompatibility complex (MHC) Class II molecules and a marker expressed on a subset of helper T-lymphocytes (Th) as well as sIgM, CD1 and a MHC Class II+ monocyte/macrophage marker. The T-lymphocyte cell lines were used to evaluate antigen-induced lymphoproliferative (LP) responses in a titration assay with HKC, BASA and gamma-irradiated B. abortus (gamma BA) antigens. The results indicate that most of the cells in many of the cell lines were typical activated T-lymphocytes as determined by surface marker expression and included cells positive for all T-lymphocyte markers tested. The cell lines contained no B-lymphocytes or mononuclear phagocytes. However, two cell lines contained significant populations (> 80%) of CD2-, CD4-, CD6-, CD8- cells that were both responsive to exogenous rBoIL-2 and were capable of exhibiting antigen-induced LP responses. In 22 of the 32 cell lines tested, gamma BA was superior to HKC at nearly every concentration tested in stimulating LP responses. This observation was independent of the immunization used to prime the T-lymphocytes in vivo. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed proteins with relative molecular masses common to all three antigen preparations as well as significant (P < 0.05) quantitative and qualitative differences in individual proteins between HKC and gamma BA. Together, the results suggest gamma BA may provide an in vitro antigenic stimulus which is deficient in HKC.

Antibody response to Brucella outer membrane proteins in bovine brucellosis: immunoblot analysis and competitive enzyme-linked immunosorbent assay using monoclonal antibodies

Sera from Brucella-infected bovines were analyzed by immunoblotting by using sonicated cell extracts of B. melitensis or B. abortus and a competitive enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies against outer membrane proteins (OMPs) with molecular masses of 10, 16.5, 19, 25 to 27, 36 to 38, and 89 kDa. Antibody responses against OMPs were compared with antibody responses against smooth lipopolysaccharide. Immunoblot analysis indicated that the antibody response in infected animals was largely different from one animal to another. The antigens of concern were OMPs with molecular masses of 10, 16.5, 19, 25 to 27, 36 to 38, and 89 kDa and other proteins with molecular masses of between 40 and 80 kDa. According to the specificity of the competitive ELISA, OMPs useful for the detection of infected animals are the OMPs of 10, 16.5, 19, 25 to 27, and 36 to 38 kDa. A competitive ELISA with the anti-89 kDa monoclonal antibody was not specific. Results of the competitive ELISA confirmed the individual variability of the humoral immune response against OMPs. It therefore seems that a combination of several protein antigens is necessary for the development of an immunoassay with a sensitivity comparable to that of the smooth lipopolysaccharide ELISA.

Bacterial survival, lymph node changes, and immunologic responses of cattle vaccinated with standard and mutant strains of Brucella abortus

Forty-eight cattle were used in 4 experiments; 6-week-old calves in experiments 1-3 (n = 24) and 10-month-old heifers in experiment 4 (n = 24). In experiments 1-3, 7 groups of 3 calves each were inoculated SC with 5 strains of Brucella abortus: virulent strain 2308 (2 groups), vaccine strain 19 (2 groups), and mutant strains RB51. 19 delta 31K, and 19 delta SOD. Sera and lymph node tissues were examined at 2-week intervals for evidence of infection. At postinoculation (PI) week 12, 2 calves in each group were given dexamethasone for 5 days. Calves were then euthanatized and lymphoid tissue, spleen, liver, and bone marrow were examined for evidence of B abortus. Calves given strain 2308 had large numbers of bacteria in their lymph nodes, marked granulomatous lymphadenitis in the deep cortex, and loss of lymphoid cells in superficial cortical areas. In addition, they had high serum antibody titers at PI week 16. Calves given strain 19, or genetic mutants derived from strain 19, cleared bacteria from lymph nodes more rapidly, had less lymphoid destruction, and developed antibody titers that did not persist for 16 weeks. The RB51 strain (rough) was cleared most rapidly from lymphoid tissues and induced serum antibody responses only to the core of the lipopolysaccharide molecule. Treatment of calves with dexamethasone did not cause B abortus to reappear in tissues of any calves, nor did serum antibody titers increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of brucellosis in Kuwait by vaccination of cattle, sheep and goats with Brucella abortus strain 19 or Brucella melitensis strain Rev. 1

In Kuwait, approximately 12,000 dairy cows were vaccinated with a reduced dose of 3 x 10(9) Brucella abortus strain 19 and approximately 350,000 sexually mature sheep and goats with a reduced dose of 10(7) B. melitensis strain Rev. 1. Using the criteria of prevaccinal and postvaccinal incidences of antibodies, abortions, and human cases of brucellosis, the programme was very successful. Widespread vaccination of adult animals is the most effective method of controlling brucellosis among cattle, sheep and goats in many countries.