Strain RB51 Research Articles

Prevention of lethal experimental infection of C57BL/6 mice by vaccination with Brucella abortus strain RB51 expressing Neospora caninum antigens

Bovine abortions caused by the intracellular protozoal parasite Neospora caninum are a major concern to cattle industries worldwide. A strong Th1 immune response is required for protection against N. caninum. Brucella abortus strain RB51 is currently used as a live, attenuated vaccine against bovine brucellosis. Strain RB51 can also be used as an expression vector for heterologous protein expression. In this study, putative protective antigens of N. caninum MIC1, MIC3, GRA2, GRA6 and SRS2, were expressed individually in B. abortus strain RB51. The ability of each of the recombinant RB51 strains to induce N. caninum-specific immunity was assessed in C57BL/6 mice. Mice were immunised by two i.p. inoculations, 4 weeks apart. Five weeks after the second immunisation, spleen cells from the vaccinated mice secreted high levels of IFN-γ and IL-10 upon in vitro stimulation with N. caninum whole cell lysate antigens. N. caninum-specific antibodies of both IgG1 and IgG2a subtypes were detected in the serum of the vaccinated mice. Mice in the vaccinated and control groups were challenged with 2×107N. caninum tachyzoites i.p. and observed for 28days after vaccination. All unvaccinated control mice died within 7days. Mice in the MIC1 and GRA6 vaccine groups were completely protected while the mice in the SRS2, GRA2 and MIC3 vaccinated groups were partially protected and experienced 10–50% mortality. The non-recombinant RB51 vector control group experienced an average protection of 69%. These results suggest that expression of protective antigens of N. caninum in B. abortus strain RB51 is a novel approach towards the development of a multivalent vaccine against brucellosis and neosporosis.

Specific T lymphocyte citotoxicity induced by Cu/Zn superoxide dismutase from Brucella abortus RB51 (B124)

Abstract Brucellosis is an infectious disease affecting animals and humans, caused mainly by B. abortus. Although several vaccines have been developed, B. abortus strain RB51 is the most used for cattle, but is not useful for humans since it causes severe granulomas. To develop a vaccine for humans, Cu-Zn superoxide dismutase (SOD Cu/Zn) has been identified as an antigen which induces T-cell mediated immunity in mice vaccinated with live Escherichia coli expressing B. abortus SOD Cu/Zn or a plasmid DNA carrying the gene sodC. The aim of this work was to demonstrate the induction by SOD Cu/Zn from B. abortus RB51 of specific cytotoxic T lymphocytes (CTL) recognizing in vitro macrophages infected with B. abortus strain RB51 or 2308. The protein was extracted from recombinant E. coli-pBAD-SOD and purified in a Ni-agarose column, and then by FPLC in a molecular weight exclusion column. Fractions corresponding to 20–22 KDa were collected and mice were immunized intramuscularly with three doses of 25 μg of SOD Cu/Zn each. T lymphocytes purified from spleen with an anti CD90 coupled to magnetic beads, were tested in an in vitro cytotoxicity assay, using J774A.1 cell line infected with B. abortus strain RB51 or 2308 as target. CTL activation was evident in both cases, since macrophages infected with any bacterial strain were killed as demonstrated by neutral red dye uptake or lactate dehydrogenase release assays. These results demonstrated that the protein by itself is able to prime pCTL to kill macrophages infected with B. abortus, no matter its virulence. Grants from CONACyT 44837-Q and SIP 20060688 and 20070239.

The role of the vacB gene in the pathogenesis of Brucella abortus

Brucella species are important zoonotic pathogens affecting a wide variety of mammals. Therefore, the identification of new Brucella virulence factors is of great interest in understanding bacterial pathogenesis and immune evasion. In this study, we have identified Brucella abortus vacB gene that presents 2343 nucleotides and 781 amino acids and it shows 39% identity with Shigella flexneri vacB gene that encodes an exoribonuclease RNase R involved in bacterial virulence. Further, we have inactivated Brucella vacB by gene replacement strategy generating a deletion mutant strain. In order to test the role of Brucella vacB in pathogenesis, BALB/c and interferon regulatory factor-1 (IRF-1) knockout (KO) mice received Brucella vacB mutant, the virulent parental strain 2308 or the vaccine strain RB51 and the bacterial CFU numbers in spleens and mous survival were monitored. Our results demonstrated that the B. abortus ΔvacB mutant and the wild type strain 2308 showed similar CFU numbers in BALB/c mice. Additionally, IRF-1 KO mice that received either the vacB mutant or S2308 strain died in 12–14 days postinfection; in contrast, all animals that received the RB51 vaccine strain survived for 30 days postinoculation. In summary, this study reports that the vacB gene in B. abortus has no impact on bacterial pathogenesis.

Safety of B. abortus rough mutant strain RB51 administration in Buffalo cows

The objective of this study was to determine if B. abortus rough mutant strain RB51 is eliminated in Buffalo milk. Five milk buffaloes were inoculated with the triple of the recommended calfhood dose (3.0 – 10.2 x 1010 cfu/ml) of B. abortus RB51 strain by subcutaneous route in the right axillary region. Milk samples were taken aseptically on a daily basis for the first 30 days and weekly for the second and third months. The samples were inoculated on Brucella Medium Base (BMB) (Oxoid) and Rifampin Brucellae Medium (RBM) and incubated under 10% CO2 at 37°C for 10 days. The suspicious colonies were recultured in BMB and RBM. PCR analysis was also performed on milk samples.There were no isolations of bacteria with characteristics of Brucella from any of the milk samples collected during 90 days of the study. However Brucella RB51 DNA was detected on day 2 and 3 post vaccination in one buffalo cow and on day 21 post vaccination in another buffalo cow.It was concluded that the strain used at this dose wasn’t eliminated by milk in Buffaloes inoculated during lactation, however PCR positive results underline the necessity of milk pasteurization in order to minimize food-chain exposure.

Immune Responses of Elk to Initial and Booster Vaccinations withBrucella abortusStrain RB51 or 19

Previous studies have suggested that currently available brucellosis vaccines induce poor or no protection in elk (Cervus elaphus nelsoni). In this study, we characterized the immunologic responses of elk after initial or booster vaccination with Brucella abortus strains RB51 (SRB51) and 19 (S19). Elk were vaccinated with saline or 10(10) CFU of SRB51 or S19 (n=seven animals/treatment) and booster vaccinated with a similar dosage of the autologous vaccine at 65 weeks. Compared to nonvaccinates, elk vaccinated with SRB51 or S19 had greater (P<0.05) antibody responses to SRB51 or S19 after initial vaccination and after booster vaccination. Compared to nonvaccinated elk, greater (P<0.05) proliferative responses to autologous antigen after initial vaccination occurred at only a few sample times in SRB51 (6, 14, and 22 weeks) and S19 (22 weeks) treatment groups. In general, proliferative responses of vaccinates to nonautologous antigens did not differ (P>0.05) from the responses of nonvaccinated elk. Gamma interferon production in response to autologous or nonautologous Brucella antigens did not differ (P>0.05) between controls and vaccinates after booster vaccination. Flow cytometric techniques suggested that proliferation occurred more frequently in immunoglobulin M-positive cells, with differences between vaccination and control treatments in CD4+ and CD8+ subset proliferation detected only at 22 weeks after initial vaccination. After booster vaccination, one technique ([3H]thymidine incorporation) suggested that proliferative responses to SRB51 antigen, but not S19 antigen, were greater (P<0.05) in vaccinates compared to the responses of nonvaccinates. However, in general, flow cytometric and other techniques failed to detect significant anamnestic responses to autologous or nonautologous Brucella antigens in S19 or SRB51 vaccinates after booster vaccination. Although some cellular immune responses were detected after initial or booster vaccination of elk with SRB51 or S19, our data suggest that responses tend to be transient and much less robust than previously reported in SRB51-vaccinated cattle (Bos taurus) or bison (Bison bison). These data may explain why the vaccination of elk with S19 and SRB51 induces poor protection against brucellosis.

Parenteral vaccination of domestic pigs with Brucella abortus strain RB51

To determine the immunogenicity and efficacy of Brucella abortus strain RB51 (SRB51) as a vaccine in domestic pigs. Sixty-eight 6-week-old crossbred domestic pigs and twenty-four 4-month-old gilts. In experiment 1, pigs were vaccinated IM (n = 51) with 2 x 10(10) CFUs of SRB51 or sham inoculated (17). Periodic blood samples were obtained to perform blood cultures, serologic evaluations, and cell-mediated immunity assays. Necropsies were performed at selected times between weeks 1 and 23 after vaccination to determine vaccine clearance. In experiment 2, gilts were similarly vaccinated (n = 18) or sham inoculated (8) and similar samples were obtained after vaccination. Gilts were bred and challenged conjunctivally with 5.0 x 10(7) CFUs of virulent Brucella suis strain 3B. Necropsies were performed on gilts and on fetuses or neonates after abortion or parturition, respectively. Bacterial cultures and serologic evaluations were performed on samples obtained at necropsy to determine vaccine efficacy. Humoral and cell-mediated immune responses did not differ between vaccinates and controls. After vaccination, SRB51 was not isolated from blood cultures of either group and was isolated from lymphoid tissues of 3 pigs at 2 weeks (n = 2) and 4 weeks (1) after vaccination. No differences were found in isolation of B suis or in seroconversion between vaccinated and control gilts and between their neonates or aborted fetuses. Parenteral vaccination with SRB51 does not induce humoral or cell-mediated immune responses. Vaccination with SRB51 did not protect gilts or their neonates and fetuses from virulent challenge with B suis.

Deletion of znuA Virulence Factor Attenuates Brucella abortus and Confers Protection against Wild-Type Challenge

znuA is known to be an important factor for survival and normal growth under low Zn(2+) concentrations for Escherichia coli, Haemophilus spp., Neisseria gonorrhoeae, and Pasteurella multocida. We hypothesized that the znuA gene present in Brucella melitensis 16 M would be similar to znuA in B. abortus and questioned whether it may also be an important factor for growth and virulence of Brucella abortus. Using the B. melitensis 16 M genome sequence, primers were designed to construct a B. abortus deletion mutant. A znuA knockout mutation in B. abortus 2308 (DeltaznuA) was constructed and found to be lethal in low-Zn(2+) medium. When used to infect macrophages, DeltaznuA B. abortus showed minimal growth. Further study with DeltaznuA B. abortus showed that its virulence in BALB/c mice was attenuated, and most of the bacteria were cleared from the spleen within 8 weeks. Protection studies confirmed the DeltaznuA mutant as a potential live vaccine, since protection against wild-type B. abortus 2308 challenge was as effective as that obtained with the RB51 or S19 vaccine strain.

Efficacy of strain RB51 vaccine in heifers against experimental brucellosis

With the goal of providing an additional tool for controlling bovine brucellosis in Brazil and evaluating the full calf dose in adult cattle, the efficacy of the rough Brucella abortus strain RB51 vaccine was tested in heifers. Thirty-three females of approximately 24 months of age were divided in two groups: one group ( n = 20) received the RB51 vaccine and the other group ( n = 13) were used as non-vaccinated control. Animals in the vaccinated group were split in two sub-groups. One sub-group ( n = 12) was vaccinated subcutaneously with 1.5 × 10 10 colony forming units (CFU) of RB51 at Day 0 of the experiment and the other sub-group ( n = 8) was vaccinated subcutaneously with 1.6 × 10 10 CFU of RB51 at 60 days of gestation (Day 260 of the experiment). All cattle were challenged between 6 and 7 months of pregnancy with 3 × 10 8 CFU of the virulent strain 2308 of B. abortus by the conjunctival route. Vaccination with RB51 vaccine did not result in the production of any antibodies against the O-side chain of lipopolysaccharide (LPS), as measured by conventional serological tests (rose bengal plate agglutination test (RBPAT), standard tube agglutination test (STAT), and 2-mercaptoethanol test (2ME)). A total of 25% cumulative incidence of abortions was found in the vaccinated group, whereas in the control group the cumulative incidence was 62%. B. abortus RB51 was not isolated from any sample, and no abortions were produced by RB51 vaccination of females at 60 days of pregnancy. The results indicate that vaccination with RB51 prevented 59.4% of abortions, 58.6% of cow infections, and 61.0% of fetal infections. The relative risk (RR) revealed that non-vaccinated animals have 2.462 (95% CI 1.029–5.889) times higher risk of aborting than RB51-vaccinated animals.

Increases of efficacy as vaccine against Brucella abortus infection in mice by simultaneous inoculation with avirulent smooth bvrS/ bvrR and rough wbkA mutants

The Brucella abortus S19 and RB51 strains are the most widely used live vaccines against bovine brucellosis. However, both can induce abortion and milk excretion, S19 vaccination interferes in serological tests, and RB51 is less effective. We have shown previously that a rough wbkA B. abortus mutant is attenuated and a better vaccine than RB51 in BALB/c mice, and that mutants in the two-component regulatory system bvrS/ bvrR are markedly attenuated while keeping a smooth lipopolysaccharide (S-LPS). In this work, we tested whether simultaneous inoculation with live bvrS increases wbkA vaccine efficacy in mice. Even at high doses, the bvrS mutant was cleared much faster from spleens than the wbkA mutant. The splenic persistence of the wbkA mutant increased when inoculated along with the bvrS mutant, but also with inactivated bvrS cells or with purified B. abortus S-LPS, strongly suggesting that S-LPS in the bvrS mutant played a determinant role in the wbkA persistence. When inoculated alone, both mutants protected against virulent B. abortus but less than when inoculated simultaneously, and the protection afforded by the combination was better than that obtained with B. abortus S19. Increased protection was also obtained after simultaneous inoculation of the wbkA mutant and inactivated bvrS cells or purified S-LPS, showing again the role played by the S-LPS in the bvrS cells. In mice, the bvrS– wbkA combination induced an antibody response reduced with respect to B. abortus S19 vaccination. Thus, the simultaneous use of live bvrS and wbkA B. abortus mutants seems a promising approach to overcome the problems of the S19 andRB51 vaccines.

Efecto de una dieta con bajo aporte de selenio sobre la respuesta inmune a la vacuna Brucella abortus Cepa RB51 en vacas lecheras

The effect of a diet with a low selenium (Se) content on the immune response to Brucella abortus Strain RB51 vaccine in dairy cows and in their serum inmunog...

Role in Virulence of aBrucella abortusProtein Exhibiting Lectin-Like Activity

Brucella abortus is a facultative, intracellular zoonotic pathogen which can cause undulant fever in humans and abortions in cattle. A 14-kDa protein of B. abortus was previously identified to be immunogenic in animals infected with Brucella spp. In this study, we discovered that the 14-kDa protein possessed immunoglobulin binding and hemagglutination properties that appeared to be based on the protein's lectin-like properties. Hemagglutination inhibition experiments suggested that the 14-kDa protein has affinity towards mannose. Disruption of the gene encoding the 14-kDa protein in virulent B. abortus strain 2308 induced a rough-like phenotype with an altered smooth lipopolysaccharide (LPS) immunoblot profile and a significant reduction in the bacterium's ability to replicate in mouse spleens. However, the mutant strain was stably maintained in mouse spleens at 2.0 to 2.6 log(10) CFU/spleen from day 1 to week 6 after intraperitoneal inoculation with 4.65 log(10) CFU. In contrast to the case for the smooth virulent strain 2308, in the rough attenuated strain RB51 disruption of the 14-kDa protein's gene had no effect on the mouse clearance pattern. These findings indicate that the 14-kDa protein of B. abortus possesses lectin-like properties and is essential for the virulence of the species, probably because of its direct or indirect role in the synthesis of smooth LPS.

Induction of Antigen-Specific Th1-Type Immune Responses by Gamma-Irradiated RecombinantBrucella abortusRB51

Brucella abortus strain RB51 is an attenuated rough mutant used as the live vaccine against bovine brucellosis in the United States and other countries. We previously reported the development of strain RB51 as a bacterial vaccine vector for inducing Th1-type immune responses against heterologous proteins. Because safety concerns may preclude the use of strain RB51-based recombinant live vaccines, we explored the ability of a gamma-irradiated recombinant RB51 strain to induce heterologous antigen-specific immune responses in BALB/c mice. Exposure of strain RB51G/LacZ expressing Escherichia coli beta-galactosidase to a minimum of 300 kilorads of gamma radiation resulted in complete loss of replicative ability. These bacteria, however, remained metabolically active and continued to synthesize beta-galactosidase. A single intraperitoneal inoculation of mice with 10(9) CFU equivalents of gamma-irradiated, but not heat-killed, RB51G/LacZ induced a beta-galactosidase-specific Th1-type immune response. Though no obvious differences were detected in immune responses to B. abortus-specific antigens, mice vaccinated with gamma-irradiated, but not heat-killed, RB51G/LacZ developed significant protection against challenge with virulent B. abortus. In vitro experiments indicated that gamma-irradiated and heat-killed RB51G/LacZ induced maturation of dendritic cells; however, stimulation with gamma-irradiated bacteria resulted in more interleukin-12 secretion. These results suggest that recombinant RB51 strains exposed to an appropriate minimum dose of gamma radiation are unable to replicate but retain their ability to stimulate Th1 immune responses against the heterologous antigens and confer protection against B. abortus challenge in mice.

Photopolymerized hydrogel carriers for live vaccine ballistic delivery

Photopolymerized poly(ethylene glycol) (PEG)-crosslinked hydrogels were assessed for their ability to serve as a payload vehicle to deliver a viable bacterial vaccine ( Brucella abortus strain RB51 (RB51) to bison in Yellowstone National Park) ballistically using thermoplastic degradable Biobullets. PEG modified with degradable glycolide or lactide oligomers capped with photopolymerizable methacrylate groups served to crosslink the hydrogel vaccine carrier inside commercial hydroxypropylcellulose Biobullets. Release of 1 μm diameter model fluorescent particles from hydrogels followed known degradation trends for glycolide- and lactide-modified PEG hydrogels. All particles were released from PEG-co-glycolide hydrogels after ∼10 days and PEG-co-lactide hydrogels after ∼45 days following gel degradation. Minimal particle release was observed from pure PEG dimethacrylate hydrogels over 40 days. P. aeruginosa (strain PAO1) and RB51 live vaccines exhibit excellent viability following exposure to photopolymerization encapsulation within these gel matrices. Hydrogels photopolymerized into the payload chamber of Biobullets exhibit similar ballistic properties to commercially available Biobullets and penetrate and remain intact when fired intramuscularly into live elk for release of their gel payload in the host.

Immunologic responses of bison to vaccination with Brucella abortus strain RB51: Comparison of parenteral to ballistic delivery via compressed pellets or photopolymerized hydrogels

This study compared responses of bison calves to 10 10 CFU of Brucella abortus strain RB51 (SRB51) delivered by parenteral or ballistic methods. Two types of biobullet payloads were evaluated; compacted SRB51 pellets or SRB51 encapsulated in photopolymerized poly(ethylene glycol) hydrogels. Bison were vaccinated with saline, parenteral SRB51 alone, or in combination with Spirovac™, or ballistically with compressed SRB51 or hydrogel biobullets. Bison parenterally vaccinated with SRB51 had greater ( P < 0.05) immunologic responses when compared to control bison. Co-administration of Spirovac™ as an adjuvant did not influence immunologic responses. As compared to compressed SRB51 biobullets, ballistic vaccination with hydrogel biobullets increased cellular immune responses at some sampling times. Our data suggest that hydrogel formulations of SRB51 may be a superior alternative to compressed SRB51 tablets for ballistic vaccination of bison. Although preliminary, data suggests that immunologic responses of bison to SRB51 hydrogel bullets are similar to responses after parenteral vaccination with SRB51.

Existing and future vaccines against brucellosis in small ruminants

Conjunctival vaccination with Rev-1 is the best method available for controlling Brucella melitensis infection. The rough RB51 and VRTM1 strains do not interfere with diagnosis, but are ineffective in sheep or goats. Recombinant vaccine strains deleted in genes for relevant proteins associated to diagnostic tests are, for the moment, ineffective. DNA-based vaccines are not available. Inactivated vaccines in new generation adjuvants are being also investigated.

Serologic responses, biosafety and clearance of four dosages of Brucella abortus strain RB51 in 6–10 months old water buffalo ( Bubalus bubalis)

Thirty water buffalo were obtained from a brucellosis-free farm in order to evaluate antibody responses, bacterial clearance and safety to Brucella abortus strain RB51 vaccine in a dose response study. The animals were randomly divided into five treatment groups. Groups I–V received the recommended dose of RB51 vaccine (RD) once, RD twice 4 weeks apart, double RD once, double RD twice 4 weeks apart and saline once, respectively. Antibody responses to RB51 were monitored at 2, 4, 6, 8, 10, 12, 16 18, 22, 24 and 27 post-initial-inoculation weeks (PIW). Clearance of RB51 from the prescapular lymph node was evaluated at 2, 4, 6, 12, 18 and 24 PIW for groups 1, III and V and at 6, 8, 10, 16, 22 and 27 PIW for groups II and IV. To evaluate shedding of the RB51 strain, nasal, conjunctival, vaginal or preputial swabs were taken from all experimental animals at 1, 2, 3, 4, 6, 8 and 12 PIW. Sera taken at all PIW were negative for field strain B. abortus by both the buffered plate agglutination test (BPAT) and competitive enzyme-linked immunosorbent assay (c-ELISA). Antibody responses to RB51 were demonstrated in all vaccinates but not in the controls, up to 12 PIW, by complement fixation test (CFT) and the dot-blot assay with an 83.7% agreement for both tests. Clearance of RB51 occurred between 6 and 12 PIW in group I but less than 2 weeks after booster vaccinations in groups II and IV and between 4 and 6 PIW in group III. RB51 was not recovered at any time from swabs obtained from either RB51-vaccinates or non-vaccinates. The results of this study indicate that serologic responses to RB51 vaccination can be monitored by both CFT and dot-blot assay in water buffalo. Our data also indicates that RB51 vaccination does not interfere with brucellosis sero-surveillance and is safe (no serological and bacteriological evidence of spread to non-vaccinates, no adverse clinical signs or detectable abnormalities on haematology and serum biochemistry) for use in water buffalo.

Protective properties of rifampin-resistant rough mutants of Brucella melitensis.

Vaccination against Brucella infections in animals is usually performed by administration of live attenuated smooth B. abortus strain S19 and B. melitensis strain Rev1. They are proven effective vaccines against B. abortus in cattle and against B. melitensis and B. ovis in sheep and goats, respectively. However, both vaccines have the main drawback of inducing O-polysaccharide-specific antibodies that interfere with serologic diagnosis of disease. In addition, they retain residual virulence, being a cause of abortion in pregnant animals and infection in humans. To overcome these problems, one approach is to develop defined rough mutant Brucella strains lacking O antigen of lipopolysaccharide. B. abortus rough strain RB51, a rifampin-resistant mutant of virulent strain B. abortus 2308, is used as a vaccine against B. abortus infection in cattle in some countries. However, RB51 is not effective in sheep, and there is only preliminary evidence that it is effective in goats. In this study, we tested the efficacies of six rifampin-resistant rough strains of B. melitensis in protecting BALB/c mice exposed to B. melitensis infection. The protective properties, as well as both humoral and cellular immune responses, were assessed in comparison with those provided by B. melitensis Rev1 and B. abortus RB51 vaccines. The results indicated that these rough mutants were able to induce a very good level of protection against B. melitensis infection, similar to that provided by Rev1 and superior to that of RB51, without inducing antibodies to O antigen. In addition, all B. melitensis mutants were able to stimulate good production of gamma interferon. The characteristics of these strains encourage further evaluation of them as alternative vaccines to Rev1 in primary host species.

Evaluation of cell-mediated immune responses and bacterial clearance in 6–10 months old water buffalo ( Bubalus bubalis) experimentally vaccinated with four dosages of commercial Brucella abortus strain RB51 vaccine

Thirty water buffalo, obtained from a brucellosis-free farm, were used to evaluate cell-mediated immune responses and bacterial clearance in response to vaccination with Brucella abortus strain RB51 (RB51) in a dose-response study. The animals were randomly divided into five treatment groups. Groups I–V received the recommended dose (RD) of RB51 vaccine once, RD twice 4 weeks apart, double RD once, double RD twice 4 weeks apart and saline once, respectively. Cell-mediated immune response to RB51 was assessed by the histological examination of haematoxylin and eosin (H&E) stained sections of lymph nodes draining the sites of inoculation and by comparison of stimulation indices (SI) derived from gamma interferon (IFN-γ) assay. A mixture of cytoplasmic proteins from B. melitensis B115 (brucellergene) was used as a specific antigenic stimulus to peripheral blood mononuclear cells (PBMC) and lymph node mononuclear cells (LNMC) up to 22 post-initial-inoculation week (PIW). Supernatants harvested at 18–24 h after the in vitro antigenic stimulus were assayed for their IFN-γ content by using a commercial sandwich enzyme-linked immunosorbent assay (ELISA) kit. Clearance of RB51 was assessed by the sequential immunohistochemical examination of sections of draining lymph nodes post-inoculation. There was no observable expansion of the deep cortex of lymph nodes on H&E sections indicating poor T-cell stimulation. All group V (control) water buffalo PBMC ELISA values were negative (SI < 2.2) at all PIW sampling intervals. Overall PBMC IFN-γ assay detected vaccinates from treatment groups’ I–IV 67% (4/6), 83% (5/6), 33% (2/6) and 67% (4/6), respectively. LNMC IFN-γ assay was unimpressive and there was a negative correlation (−0.08) between the results of PBMC and LNMC of IFN-γ assay. Clearance of RB51 occurred between 4 and 6 PIW in treatment groups I and III and between 6 and 12 PIW in groups II and IV. RB51 was not detected in any of the control animals at sampling intervals post-inoculation.

Improved Expression Vector for Brucella Species

We constructed an improved vector pNSGroE for gene expression stud-ies in Brucella spp. It is derived from the broad host range cloning vector pBBR1MCS (1). This new plasmid has several advantages over pBBR1MCS or its derivatives pBBGroE (2): (i) it is smaller in size, 2.9 kb; (ii) it expresses proteins as His-tagged fusion for easy detection and purification; (iii) it car-ries the groE promoter for constitutive expression that is enhanced under con-ditions of stress in vitro and in vivo; and (iv) it has higher levels of heterologous protein expression. Our expression studies in Brucella abortus strain RB51 indicated that the level of heterologous protein expression is higher with pNS-GroE compared to pBBGroE vector. We have also demonstrated the ability of the new vector to express heterolo-gous fusion proteins stably in Brucella species. The smaller size of the new vector was achieved by combining only the very essential elements for replica-tion and expression [minimum origin of replication, promoter, antibiotic selection marker, and multiple cloning sites (MCS)] and removing all nones-sential elements in the original vector pBBR1MCS or pBBGroE (lacZ gene, mobilization gene, and 1 kb upstream of the groE promoter). The vector was constructed by excision of a 185-bp fragment containing the MCS of pRSETA vector (Invitrogen, Carlsbad, CA, USA) using XbaI and HindIII. This fragment was cloned into XbaI and HindIII sites of pGEM11 vector (Promega, Madison, WI, USA) to form construct A. The groE promoter of Brucella spp. was amplified from the genomic DNA of B. abortus strain 2308 using Platinum

Safety of Brucella abortus strain RB51 in black bears.

In two studies conducted from October 1999 to March 2000 and December 2000 to April 2001, adult black bears (Ursus americanus) were orally inoculated with 1.4-3.1 x 10(10) colony-forming units (CFU) of Brucella abortus strain RB51 (SRB51, n=12) or 2 ml of 0.15 M NaCl solution (saline, n=11). We did not detect a difference (P>0.05) in antibody titers to SRB51 in serum obtained before vaccination, at 8 wk after vaccination, or at necropsy at 21 or 23 wk after vaccination between SRB51-vaccinated and nonvaccinated bears. The SRB51 vaccine strain was recovered from tissues obtained at necropsy from one of six SRB51-vaccinated bears in study 1, but none of the six SRB51-vaccinated bears in study 2. Vaccination of black bears with SRB51 did not appear to influence (P>0.05) reproductive performance.