Major histocompatibility complex class I and II expression on macrophages containing a virulent strain of Brucella abortus measured using green fluorescent protein-expressing brucellae and flow cytometry

Immune responses appropriate for control of an intracellular pathogen are generated in mice infected with Brucella abortus, shown by the ability of T cells to adoptively transfer resistance to naive mice. The infection nevertheless persists for months. It was hypothesized that one factor in maintaining the infection despite the presence of immune T cells was suboptimal expression of major histocompatibility complex (MHC) molecules on macrophages containing brucellae. This would allow B. abortus to elude detection by the host's immune system. To test this, B. abortus organisms expressing green fluorescent protein (GFP-Brucella) were constructed and three-color flow cytometry used to evaluate MHC expression on macrophages following in vitro or in vivo infection. When infected in vitro, the levels of MHC class I and class II expression on J774 macrophages containing GFP-Brucella were the same or higher than on macrophages without GFP-Brucella in the same cultures. Similarly, the MHC expression was higher on GFP(+) peritoneal exudate cells following infection or phagocytosis of heat-killed GFP-Brucella than it was on uninfected peritoneal exudate cells. Following in vivo infection of mice the level of MHC class I and II expression on GFP(+) cells in their spleens (the main site of infection) also tended to be as high as or higher than that on the GFP-negative cells. The only in vivo GFP(+) cells that showed a decreased MHC expression was a population of splenic Mac1(+) cells recovered from interferon-gamma gene-disrupted mice at the time of their death due to an overwhelming number of bacteria per spleen. Overall, it was concluded that decreased MHC expression is not a general principle associated with brucella infection of macrophages and thus not likely to contribute to maintenance of the chronic infection.

Re-examination of the role of the Brucella melitensis HtrA stress response protease in virulence in pregnant goats

Based on previously reported studies describing the experimental infection of pregnant goats with B. melitensis strain RWP5, we proposed that the HtrA protease plays an important role in the virulence of B. melitensis in its natural ruminant host. Subsequent studies, however, have shown that RWP5 is actually an htrA cycL double mutant. In order to definitively evaluate the role of the B. melitensis htrA in virulence, we constructed an authentic htrA mutant and examined this strain in pregnant goats. The findings of these studies indicate that the contribution of the htrA gene product to the virulence of B. melitensis in its natural host is not as great as was previously proposed.

Brucella abortus HtrA functions as an authentic stress response protease but is not required for wild-type virulence in BALB/c mice

A second mutation has recently been identified in the previously described Brucella abortus htrA mutant PHE1. As a result of this finding, a new B. abortus htrA mutant, designated RWP11, was constructed to evaluate the biological function of the Brucella HtrA protease. RWP11 is more sensitive to oxidative killing in vitro and less resistant to killing by cultured murine neutrophils and macrophages than the virulent parental strain 2308 but is not attenuated in BALB/c mice through 4 weeks postinfection. The in vitro phenotype of B. abortus RWP11 is consistent with the proposed function of bacterial HtrA proteases as components of a secondary line of defense against oxidative damage. The in vivo phenotype of this mutant, however, indicates that, unlike the corresponding Salmonella and Yersinia proteins, Brucella HtrA does not play a critical role in virulence in the mouse model.

Attenuation and immunogenicity of a Brucella abortus htrA cycL double mutant in cattle

PHE1 is a htrA cycL double gene deletion mutant of virulent Brucella abortus strain 2308 (S2308) which has previously been evaluated in the murine and caprine models of bovine brucellosis. This report describes the results of studies conducted with this mutant in the natural bovine host. Six sexually mature, non-gravid heifers were inoculated via the conjunctival sac with 1 x 10(10) colony forming units (CFU) of either the parental S2308 or the htrA cycL gene deletion mutant, PHE1. At 4, 7 and 11 days post-inoculation, PHE1 was found to colonize the bovine host at lower levels than S2308. In a second experiment, eight heifers in mid-gestation were infected with 1 x 10(7) CFU of either strain via the conjunctival sac. The virulent S2308 caused abortions or weak calves in 4/4 cows, while all four cows infected with PHE1 had healthy calves. Furthermore, PHE1 exhibited decreased resistance to killing by cultured bovine neutrophils and macrophages compared to the parental strain. These studies demonstrate that the B. abortus htrA cycL gene deletion mutant PHE1 is highly attenuated in the bovine host when compared to the virulent parental S2308.

The Brucella abortus CcrM DNA methyltransferase is essential for viability, and its overexpression attenuates intracellular replication in murine macrophages

The CcrM DNA methyltransferase of the alpha-proteobacteria catalyzes the methylation of the adenine in the sequence GAnTC. Like Dam in the enterobacteria, CcrM plays a regulatory role in Caulobacter crescentus and Rhizobium meliloti. CcrM is essential for viability in both of these organisms, and we show here that it is also essential in Brucella abortus. Further, increased copy number of the ccrM gene results in striking changes in B. abortus morphology, DNA replication, and growth in murine macrophages. We generated strains that carry ccrM either on a low-copy-number plasmid (strain GR131) or on a moderate-copy-number plasmid (strain GR132). Strain GR131 has wild-type morphology and chromosome number, as assessed by flow cytometry. In contrast, strain GR132 has abnormal branched morphology, suggesting aberrant cell division, and increased chromosome number. Although these strains exhibit different morphologies and DNA content, the replication of both strains in macrophages is attenuated. These data imply that the reduction in survival in host cells is not due solely to a cell division defect but is due to additional functions of CcrM. Because CcrM is essential in B. abortus and increased ccrM copy number attenuates survival in host cells, we propose that CcrM is an appropriate target for new antibiotics.

Similar requirements of a plant symbiont and a mammalian pathogen for prolonged intracellular survival

Brucella abortus, a mammalian pathogen, and Rhizobium meliloti, a phylogenetically related plant symbiont, establish chronic infections in their respective hosts. Here a highly conserved B. abortus homolog of the R. meliloti bacA gene, which encodes a putative cytoplasmic membrane transport protein required for symbiosis, was identified. An isogenic B. abortus bacA mutant exhibited decreased survival in macrophages and greatly accelerated clearance from experimentally infected mice compared to the virulent parental strain. Thus, the bacA gene product is critical for the maintenance of two very diverse host-bacterial relationships.

The Brucella abortus Lon functions as a generalized stress response protease and is required for wild-type virulence in BALB/c mice

The gene encoding a Lon protease homologue has been cloned from Brucella abortus. The putative Brucella abortus Lon shares > 60% amino acid identity with its Escherichia coli counterpart and the recombinant form of this protein restores the capacity of an Escherichia coli lon mutant to resist killing by ultraviolet irradiation and regulate the expression of a cpsB:lacZ fusion to wild-type levels. A sigma32 type promoter was identified upstream of the predicted lon coding region and Northern analysis revealed that transcription of the native Brucella abortus lon increases in response to heat shock and other environmental stresses. ATP-dependent proteolytic activity was also demonstrated for purified recombinant Lon. To evaluate the capacity of the Brucella abortus Lon homologue to function as a stress response protease, the majority of the lon coding region was removed from virulent strain Brucella abortus 2308 via allelic exchange. In contrast to the parent strain, the Brucella abortus lon mutant, designated GR106, was impaired in its capacity to form isolated colonies on solid medium at 41 degrees C and displayed an increased sensitivity to killing by puromycin and H2O2. GR106 also displayed reduced survival in cultured murine macrophages and significant attenuation in BALB/c mice at 1 week post infection compared with the virulent parental strain. Beginning at 2 weeks and continuing for 6 weeks post infection, however, GR106 and 2308 displayed equivalent spleen and liver colonization levels in mice. These findings suggest that the Brucella abortus Lon homologue functions as a stress response protease that is required for wild-type virulence during the initial stages of infection in the mouse model, but is not essential for the establishment and maintenance of chronic infection in this host.

The Brucella abortus host factor I (HF-I) protein contributes to stress resistance during stationary phase and is a major determinant of virulence in mice

Brucella abortus is a facultative intracellular pathogen that causes abortion and infertility in domestic animals and a severe debilitating febrile illness in humans. The mechanisms that this highly successful intracellular pathogen uses to adapt to, and survive within, the harsh intracellular environment of the host macrophage are presently unknown. Maintenance of the stationary phase growth state has been proposed to be critical for the virulence of several mammalian pathogens, but analysis of this relationship for the brucellae has not been undertaken. In order to evaluate this relationship, we examined the in vitro and in vivo characteristics of an isogenic hfq mutant constructed from virulent Brucella abortus 2308. In Escherichia coli, the hfq gene product is an RNA-binding protein that participates in the regulation of stationary phase stress resistance, at least partly by enhancing translation of the stationary phase-specific sigma factor RpoS. As expected, the Brucella abortus hfq mutant, designated Hfq3, showed increased sensitivity to H2O2, and decreased survival under acidic conditions (pH 4.0), during stationary phase growth compared with 2308. Hfq3 was also less able to withstand prolonged starvation than 2308. The Brucella abortus hfq mutant, unlike its parental strain 2308, fails to replicate in cultured murine macrophages, and is rapidly cleared from the spleens and livers of experimentally infected BALB/c mice. These findings suggest that the Brucella abortus hfq gene product makes an essential contribution to pathogenesis in mice, probably by allowing the brucellae to adapt appropriately to the harsh environmental conditions encountered within the host macrophage.

The siderophore 2,3-dihydroxybenzoic acid is not required for virulence of Brucella abortus in BALB/c mice

2,3-Dihydroxybenzoic acid (DHBA) is the only siderophore described for Brucella, and previous studies suggested that DHBA might contribute to the capacity of these organisms to persist in host macrophages. Employing an isogenic siderophore mutant (DeltaentC) constructed from virulent Brucella abortus 2308, however, we found that production of DHBA is not required for replication in cultured murine macrophages or for the establishment and maintenance of chronic infection in the BALB/c mouse model.

Identification and characterization of a 14-kilodalton Brucella abortus protein reactive with antibodies from naturally and experimentally infected hosts and T lymphocytes from experimentally infected BALB/c mice

A low-molecular-weight recombinant Brucella abortus protein reactive with antibodies from a variety of naturally and experimentally infected hosts and T lymphocytes from experimentally infected mice was identified and given the designation BA14K. The gene encoding BA14K was cloned and characterized, and the predicted amino acid sequence of this immunoreactive protein showed no significant homology with previously described proteins. Sequences homologous to the cloned fragment encoding BA14K were identified by Southern blot analysis of genomic DNAs from representatives of all of the currently recognized Brucella species. Studies employing BA14K should contribute to our efforts to better understand the antigenic specificity of protective immunity to brucellosis.

A Brucella melitensis high-temperature-requirement A (htrA) deletion mutant is attenuated in goats and protects against abortion

It has been previously demonstrated that a Brucella melitensis high-temperature-requirement A (htrA) deletion mutant is more susceptible to oxidative killing in vitro than the parental strain and is attenuated in mice. To evaluate the contribution of the B melitensis HtrA protease to virulence in ruminants, the capacity of the B melitensis htrA mutant RWP5 to produce abortion in goats was compared to that of the virulent parental strain 16M. Experimental infection with strain 16M caused abortion in eight of 12 pregnant nannies, while none of the 12 nannies inoculated with RWP5 aborted. Furthermore, intramuscular injection of fetuses in utero with RWP5 led to colonisation of the fetus with subsequent colonisation of the nanny, but no abortion was observed. Nannies vaccinated with RWP5 showed complete protection against abortion when challenged with 16M during the third trimester of pregnancy. However, these animals were not protected from colonisation by 16M. The results presented here clearly indicate that the B melitensis htrA gene product contributes to pathogenesis in goats, but the utility of B melitensis htrA mutants as vaccines in this host appears to be limited.

Cloning and nucleotide sequence analysis of a Brucella abortus gene encoding an 18 kDa immunoreactive protein

A DNA fragment encoding an approximately 18 kDa protein from Brucella abortus strain 2308 was cloned and expressed in Escherichia coli. This recombinant protein, designated BA18K, reacted in Western blot analysis with sera obtained from experimentally and naturally infected animals including mice, goats, dogs and humans. Restriction enzyme analysis of the plasmid (pBA28) encoding BA18K revealed the presence of an approximately 8.7 kbp Sau3A genomic DNA fragment within the vector and subsequent subcloning and Western blot analysis limited the region encoding BA18K to an approximately 3.0 kbp Pst 1 DNA fragment. DNA sequence analysis of this region identified an open reading frame capable of encoding a protein of 177 amino acids with a predicted relative molecular mass of 17529. Comparison of the deduced amino acid sequence of BA18K with those in the protein sequence databases yielded no homology with previously described proteins from other bacterial genera. These searches did, however, indicate that BA18K is identical to the previously described outer membrane protein (OMP) from B. abortus strain 544 designated Omp 19.

The HtrA stress response protease contributes to resistance of Brucella abortus to killing by murine phagocytes

Compared with virulent Brucella abortus 2308, the isogenic htrA mutant PHE1 shows decreased resistance to killing by cultured murine neutrophils and macrophages and significant attenuation during the early stages of infection in the BALB/c mouse model. These findings further define the contributions of the htrA gene product to the pathogenesis of B. abortus infections.

In vitro and in vivo phenotypes resulting from deletion of the high temperature requirement A (htrA) gene from the bovine vaccine strain Brucella abortus S19

An htrA deletion mutant was created in the bovine vaccine strain, B. abortus S19, by replacing the majority of the htrA gene with a kanamycin resistance gene. Antibiotic selection for a double crossover event yielded kanamycin-resistant, ampicillin-sensitive colonies confirmed by Southern and western blot analysis to be HtrA deficient. The B. abortus S19 htrA mutant was significantly more susceptible than the parental strain to killing by H2O2 (P < 0.001) and O(2)- generated by the redox cycling agent paraquat (P < 0.05) in disk sensitivity assays. Deletion of the htrA gene from S19 produced a bimodal effect on the spleen colonization profile of this strain in BALB/c mice. At one week post-infection, the B. abortus S19 htrA mutant colonized the spleens of experimentally infected BALB/c mice at significantly lower levels (P < 0.01) than the parental strain. Enhanced clearance (P < 0.05) was also observed at later timepoints, i.e. 4 and 7 weeks post infection, however at 2 and 3 weeks post infection, the mutant and parental strains colonized the mice at equivalent levels. The temporal development of specific delayed type hypersensitivity and antibody responses in BALB/c mice infected with the mutant or parental strain were equivalent. These results suggest that the htrA gene product contributes to successful host colonization by S19. However, deletion of this gene does not radically alter the overall, characteristic spleen colonization profile of this vaccine strain in the BALB/c mouse model, nor compromise the capacity of this strain to elicit Brucella cellular or humoral immune responses in this experimental host.

Behaviour of a high-temperature-requirement A (HtrA) deletion mutant of Brucella abortus in goats

Previous studies have shown that high-temperature-requirement A (HtrA) mutants of Brucella abortus are more sensitive to oxidative killing in vitro, are less able to survive in cultured murine macrophages and are attenuated in BALB/c mice. To measure the effect of an HtrA mutation on the virulence of B abortus in ruminants, pregnant goats in late gestation were exposed to infection by the conjunctival route with B abortus 2308 or an isogenic htrA mutant, PHE1. Infection with either 2308 or PHE1 resulted in abortion, but the serological responses to infection were consistent with 2308 but variable with PHE1. Strain 2308 was recovered post mortem both from aborted fetuses and infected dams, whereas PHE1 was recovered from neither. Nevertheless, short term studies revealed that PHE1 could be recovered from infected goats for up to two weeks after infection, suggesting that although the HtrA mutation may change the colonising ability of B abortus, the virulence of the mutant in pregnant goats is not reduced.

Four new derivatives of the broad-host-range cloning vector pBBR1MCS, carrying different antibiotic-resistance cassettes

Four new antibiotic-resistant derivatives of the broad-host-range (bhr) cloning vector pBBR1MCS have been constructed. These new plasmids have several advantages over many of the currently available bhr vectors in that: (i) they are relatively small (< 5.3 kb), (ii) they possess an extended multiple cloning site (MCS), (iii) they allow direct selection of recombinant plasmid molecules in Escherichia coli via disruption of the LacZ alpha peptide, (iv) they are mobilizable when the RK2 transfer functions are provided in trans and (v) they are compatible with IncP, IncQ and IncW group plasmids, as well as with ColE1- and P15a-based replicons.

Selective humoral immune response of Balb/C mice to Brucella abortus proteins expressed by vaccinia virus recombinants

Genes encoding Brucella abortus Cu/Zn superoxide dismutase (SOD) and a 54 kDa Escherichia coli HtrA homologue were cloned into shuttle plasmids pUV-1 and pSC11, and transfected into vaccinia virus to develop recombinants vUBSOD and vSB54. Control vaccinia virus recombinants vUV-1 and vSC11, carrying only the beta-gal reporter gene but no B. abortus DNA were also developed. Recombinants were analyzed in Western blotting using a polyclonal B. abortus immune serum. vUBSOD expressed a protein of apparent molecular weight of 28 kDa, composed of the 20 kDa B. abortus Cu/Zn-SOD and a protein approximately 8 kDa encoded by a portion of the vaccinia virus TK gene. vSB54 expressed a 54 kDa protein corresponding to the 54 kDa HtrA homologue. Recombinants vUSV-1 and vSC11 did not express B. abortus proteins. Groups of mice were inoculated intraperitoneally with 10(7) TCID50 of 1 of the 4 different recombinant vaccinia viruses and 5 weeks later their sera were analyzed for antibodies against vaccinia virus and B. abortus proteins. Each group of mice responded with antibodies to vaccinia virus. Sera of vSB54-inoculated mice recognized the 54 kDa HtrA homologue. vUBSOD did not induce a humoral immune response. These results represent the first report on the expression of B. abortus proteins by vaccinia virus recombinants and the first demonstrated immune response against a B. abortus protein expressed by such a recombinant.

In vivo and in vitro stability of the broad-host-range cloning vector pBBR1MCS in six Brucella species

Previous studies have shown that the broad-host-range plasmid pBBR1MCS can be used for genetic complementation in Brucella abortus. To extend these observations, the in vivo and in vitro stability of pBBR1MCS was evaluated in the six currently recognized species of the genus Brucella. pBBR1MCS was readily introduced into all of the strains tested by electroporation and was stably maintained in broth cultures without antibiotic selection during five serial passages over a 10-day period. Furthermore, isolates of all six Brucella strains containing pBBR1MCS obtained from the spleens of BALB/c mice 1 week postinfection maintained the plasmid. Although pBBR1MCS maintains the mobilization locus present in the parental plasmid pBBR1CM, attempts to detect transfer of pBBR1MCS between Brucella strains by conjugation were unsuccessful. These results demonstrate the in vitro and in vivo stability of pBBR1MCS in Brucella spp. and reinforce the usefulness of this cloning vector for the genetic analysis of these organisms.

Characterization and genetic complementation of a Brucella abortus high-temperature-requirement A (htrA) deletion mutant

In order to evaluate the biological function of the Brucella abortus high-temperature-requirement A (HtrA) stress response protein homolog, the majority of the htrA gene was deleted from the chromosome of B. abortus 2308 via gene replacement. In contrast to the parental strain, the resulting htrA deletion mutant, designated PHE1, failed to grow on solid medium at 40 degrees C and demonstrated increased sensitivity to killing by H2O2 and O2- in disk sensitivity assays. BALB/c mice were infected with strains 2308 and PHE1 to assess the effect of the htrA mutation on virulence, and significantly fewer brucellae were recovered from the spleens of mice infected with PHE1 than from those of mice infected with 2308 at 1 week postinfection. Genetic complementation studies were performed to confirm the relationship between the htrA mutation and the phenotype observed for PHE1. Plasmid pRIE1 was constructed by inserting a 1.9-kb EcoRI fragment encoding the B. abortus htrA gene into the broad-host-range plasmid pBBR1MCS. Introduction of pRIE1 into PHE1 relieved the temperature- and H2O2-sensitive phenotypes of this mutant in vitro, and PHE1(pRIE1) colonized the spleens of BALB/c mice at levels equivalent to those of the parental 2308 strain at 1 week postinfection. These results support our previous proposal that the B. abortus htrA gene product functions as a stress response protein and further suggest that this protein contributes to virulence. These studies also demonstrate the utility of the broad-host-range plasmid pBBR1MCS for genetic complementation studies in Brucella spp., establishing a key reagent for more detailed genetic analysis of this important zoonotic pathogen.

Identification of an immunoreactive Brucella abortus HtrA stress response protein homolog

An 11-kb fragment of Brucella abortus genomic DNA cloned into the BamHI site of pUC9 expressed a 60-kDa protein in Escherichia coli DH5-alpha. Antibodies reactive with this 60-kDa protein were detected by Western blot (immunoblot) analysis in sera from mice, cattle, and goats experimentally infected with B. abortus, in sera from mice experimentally infected with Brucella melitensis, and in serum from a dog experimentally infected with Brucella canis. Similar results were seen with sera obtained from cattle and dogs with naturally acquired brucellosis. The gene encoding the 60-kDa Brucella protein was localized to a 2-kb EcoRI fragment which was also reactive in Southern blots with genomic DNA from other strains of B. abortus as well as with genomic DNA from B. melitensis and B. canis. Nucleotide sequence analysis of the cloned EcoRI fragment revealed an open reading frame encoding a protein with a predicted molecular mass of 51,847 Da and an isoelectric point of 5.15. Comparison of the deduced amino acid sequence of the immunoreactive Brucella protein with the SWISS-PROT protein sequence data base revealed that it shares > 40% amino acid sequence identity with the E. coli and Salmonella typhimurium HtrA stress response proteins. Computer-assisted analysis of this amino acid sequence also predicted that the putative Brucella HtrA homolog contains an export signal sequence and a serine protease active site, two structural features characteristic of previously described HtrA proteins. A potential sigma E type heat shock promoter sequence was detected upstream of the cloned Brucella htrA gene, and Northern (RNA) blot analysis demonstrated that exposure of B. abortus 2308 to heat shock conditions resulted in a transient elevation of htrA transcription. These results strongly suggest that the immunoreactive 60-kDa Brucella protein is a member of the HtrA class of stress response proteins.

Identification and purification of a cpn60 heat shock protein homolog from Helicobacter pylori

Helicobacter pylori is associated with gastritis and peptic ulcer disease in humans. We have identified a homolog of the chaperonin cpn60 family of heat shock proteins in H. pylori, referred to as Hp54K. Hp54K, purified from water-extractable H. pylori proteins, migrated as a single band at 54 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Its native molecular mass was 740 kDa; thus, Hp54K apparently comprises a 14-mer. The N-terminal 33 residues of Hp54K exhibited 60.6, 57.6, 54.5, 54.5, 51.5, and 51.5% identity with corresponding sequences in the following cpn60 homologs: HtpB (Legionella pneumophila), P1 (human mitochondria), GroEL (Escherichia coli), BA60K (Brucella abortus), HypB (Chlamydia trachomatis), and the 65-kDa immunodominant protein of Mycobacterium bovis BCG, respectively. Hp54K was the only protein recognized in whole-cell preparations of H. pylori by immunoblotting using monospecific antisera against cpn60 homologs from L. pneumophila, E. coli, C. trachomatis, and M. bovis BCG. Antiserum against Hp54K recognized proteins with molecular masses of 50 to 60 kDa in a large number of gram-negative bacteria, consistent with the known highly conserved nature of cpn60 proteins. Hp54K is a major protein and is immunogenic in humans infected with H. pylori. Thus, Hp54K shares many similarities with known cpn60 homologs. On the basis of the proposed role of other cpn60 proteins in induction of chronic inflammation, immune cross-reactivity between Hp54K and gastric tissue may provide an important link between H. pylori infection and gastritis.

Brucella abortus deficient in copper/zinc superoxide dismutase is virulent in BALB/c mice

The gene encoding the Cu/Zn superoxide dismutase (SOD) of Brucella abortus strain 2308 was identified in a Brucella genomic library utilizing a combination of Western blotting and native gel electrophoresis. The Cu/Zn SOD gene was inactivated in vitro by ligation of a kanamycin resistance gene into the open reading frame encoding SOD. The plasmid born construct was introduced back into B. abortus by electroporation. Replacement of the wild-type Cu/Zn SOD by recombination was demonstrated by showing that both the KnR gene and the Cu/Zn SOD gene hybridized to the same band in a Southern analysis of genomic DNA. In addition, KnR strains were deficient in Cu/Zn SOD activity as assessed by lack of Cu/Zn SOD activity on a native gel and by lack of reactivity with specific serum in a Western analysis. Either strain 2308 or the Cu/Zn SOD deficient mutant injected intraperitoneally into BALB/c mice, exhibited no differences in their ability to colonize the spleen at 7 and 28 days post-inoculation. Thus, the inability to produce Cu/Zn SOD by B. abortus does not significantly impair its virulence in mice.

Molecular cloning and nucleotide sequence analysis of the gene encoding the immunoreactive Brucella abortus Hsp60 protein, BA60K

A recombinant 60 kDa Brucella abortus protein expressed in Escherichia coli was recognized in immunoblots by sera from mice experimentally infected with B. abortus and a dog experimentally infected with B. canis. Sera from humans and dogs with naturally acquired brucellosis also recognized this protein, which was designated BA60K. The gene encoding BA60K was localized within an 18 kb B. abortus genomic fragment and its direction of transcription determined by subcloning and maxicell analysis of selected restriction fragments. The nucleotide sequence of 1800 bases encompassing the predicted gene location was determined, revealing an open reading frame encoding a protein of 546 amino acids (predicted relative molecular mass of 57515). Solid phase micro-sequencing of BA60K eluted from two-dimensional polyacrylamide gels confirmed the predicted amino acid sequence. Comparison of the predicted amino acid sequence of BA60K with a protein sequence database revealed that BA60K shares 67.9% identity with the GroEL protein of E. coli, a member of the Hsp60 family of chaperonins. The immunodominant Hsp60 homologs from Legionella pneumophila, Chlamydia trachomatis and Mycobacterium tuberculosis were also found to share greater than 59% amino acid sequence identity with the BA60K protein. The identification of BA60K as a member of the Hsp60 family of chaperonins supports its role in stimulating a prominent host immune response during the course of Brucella infections. It also indicates that BA60K is an important candidate for studies aimed at identifying the antigens responsible for eliciting the protective immune response to brucellosis.

Experimental infection of goat fetuses in utero with a stable, rough mutant of Brucella abortus

Fetuses of goats in their last trimester of pregnancy were experimentally infected with Brucella abortus strain RB51, a stable rough mutant deficient in the perosamine O-chain content of its lipopolysaccharide. RB51 maintained its rough phenotype in vivo and did not induce abortion. Infection with RB51 resulted in the production of significant levels of IgG type antibodies specific for B abortus cellular antigens distinct from the perosamine O-chain. These findings suggest that strain RB51 will be useful in the pregnant goat for studying the role of brucella antigens other than the lipopolysaccharide O-chain in the immune response to brucellosis.

Biological properties of RB51; a stable rough strain of Brucella abortus

A rifampin-resistant mutant of Brucella abortus, designated RB51, was derived by repeated passage of strain 2308 on Trypticase soy supplemented with 1.5% agar and varying concentrations rifampin or penicillin. The RB51 colonies absorbed crystal violet and RB51 cell suspensions autoagglutinated, indicating a rough type colonial morphology for this strain. No O-chain component was detected in lipopolysaccharide (LPS) extracted from RB51 on SDS-PAGE gels stained with silver. Western blot analysis with the monoclonal antibody BRU 38, which is specific for the perosamine homopolymer O-chain of smooth Brucella LPS, indicated that the LPS of RB51 is highly deficient in O-chain when compared with the parenteral smooth strain 2308 or rough strain 45/20. Biochemically, RB51 resembles parental strain 2308 in its ability to utilize erythritol. Intraperitoneal inoculation of RB51 into mice results in a splenic colonization which is cleared within four weeks post infection. RB51 does not revert to smooth colony morphology upon passage in vivo (mice) or in vitro. Mice infected with RB51 produce antibodies against B. abortus antigens including class 2 and 3 outer membrane proteins but not against the O-chain. Furthermore, rabbits, goats and cattle hyperimmunized with sonicates of RB51 develop antibodies to B. abortus cellular antigens but do not develop antibodies specific for the O-chain. Immunization of mice with 1 x 10(8) viable RB51 organisms confers significant protection against challenge with virulent B. abortus strain 2308.

Serum sensitivity and lipopolysaccharide characteristics in Bordetella bronchiseptica, B. pertussis and B. parapertussis

The viability of four strains of Bordetella bronchiseptica, two strains of B. pertussis and one strain of B. parapertussis exposed to hyperimmune and pre-colostrum porcine serum was examined. Viable cell numbers (cfu/ml) of the B. pertussis strains and a rough strain of B. bronchiseptica (CSU-P-1) decreased by 99% and 99.99%, respectively, after exposure for 1 h to porcine hyperimmune serum. In contrast, smooth B. bronchiseptica strains and the B. parapertussis strain showed no significant decrease in viable cell numbers after the same treatment. B. bronchiseptica strain CSU-P-1 also showed a 99% decrease in viable cell numbers after exposure to pre-colostrum porcine serum for 1 h whereas the other strains tested showed no decrease in viable numbers under the same conditions. Heating the hyperimmune and pre-colostrum serum at 56 degrees C for 30 min resulted in the loss of bactericidal activity suggesting the involvement of complement in both systems. Analysis of silver-stained SDS-PAGE profiles of lipopolysaccharide (LPS) extracted from the bacterial cells indicated that the smooth strains of B. bronchiseptica and the B. parapertussis strain possessed high mol. wt O-side chain-like material, whereas the B. pertussis strains and B. bronchiseptica strain CSU-P-1 did not. Gel filtration of acid-hydrolysed LPS samples indicated two distinct carbohydrate peaks for the strains with high mol. wt O-side chain-like material, whereas the other strains each yielded one distinct peak. Western-blot analysis indicated a positive reaction for anti-B. bronchiseptica antibodies to the high mol. wt O-side chain-like material of all serum-resistant strains used in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid identification of smooth Brucella species with a monoclonal antibody

A colony blot enzyme-linked immunosorbent assay was developed for the rapid identification of smooth Brucella species, i.e., Brucella abortus, B. melitensis, and B. suis. Bacterial colonies from plates were blotted onto nitrocellulose disks, lysed by immersion in chloroform, and reacted with BRU 38, a rat monoclonal antibody with specificity for the O side chain of B. abortus. Reaction with anti-rat immunoglobulin G conjugated to horseradish peroxidase and development in 4-chloro-1-naphthol resulted in colonies of naturally occurring smooth Brucella species staining purple. Results could be obtained within 4 h after colonies were visible on plates and individual colonies could be detected. Yersinia enterocolitica serovar O:9 strains were the only other organisms tested which showed cross-reaction by using this procedure. Because of its speed, sensitivity, and specificity, this technique should be very useful for identifying smooth Brucella strains in diagnostic laboratories.

Virulence factors of Bordetella bronchiseptica associated with the production of infectious atrophic rhinitis and pneumonia in experimentally infected neonatal swine

Four strains of Bordetella bronchiseptica (CSU-P-1, 64-C-0406, 1120-A-83-013, and B205BT) with defined virulence for neonatal swine were examined, and an attempt was made to correlate the presence of certain in vitro phenotypic characteristics with the ability of a particular B. bronchiseptica strain to produce turbinate and lung lesions in piglets. All of the strains except CSU-P-1 colonized the nasal passages of the pigs heavily, and strains 1120-A-83-013 and B205BT produced moderate to severe nasal and lung lesions in experimentally infected piglets. All of the strains attached equally well to porcine tracheal ring explant cultures, and all of the strains except CSU-P-1 produced smooth, hemolytic colonies on Bordet-Gengou medium, agglutinated porcine erythrocytes, and possessed adenylate cyclase activity. Strains 1120-A-83-013 and B205BT produced considerably higher levels of dermonecrotic toxin activity than did strains CSU-P-1 and 64-C-0406. These results indicate that production of nasal and lung lesions in neonatal piglets by the B. bronchiseptica strains tested can be directly correlated with their level of dermonecrotic toxin production.

DNA homology studies of the catalase-negative campylobacters and "Campylobacter fecalis," an emended description of Campylobacter sputorum, and proposal of the neotype strain of Campylobacter sputorum

Twenty-three strains of catalase-negative campylobacters and five strains of "Campylobacter fecalis," which is catalase-positive, were examined by DNA hybridization experiments. These organisms formed four distinct DNA homology groups corresponding to Campylobacter sputorum, Campylobacter mucosalis, Campylobacter concisus, and a currently unnamed group referred to as the "catalase-negative or weak" (CNW) strains. The strains were further characterized to determine which phenotypic characteristics provide the most reliable identification at the species level. Campylobacter sputorum ssp. sputorum, C. sputorum ssp. bubulus, and "C. fecalis" could not be distinguished by DNA homology; consequently, it is proposed that these three taxa be considered as biovars of C. sputorum. The description of C. sputorum is emended accordingly. ATCC strain 35980 is proposed as the neotype strain of C. sputorum.

Improved biotyping schemes for Campylobacter jejuni and Campylobacter coli

Campylobacter jejuni (20 strains) and Campylobacter coli (12 strains) were assigned to four biovars for each species based on phenotypic tests that were easy to perform and interpret. The resulting biotyping schemes offer a greater degree of distinction among C. jejuni and C. coli strains than any of the other biotyping schemes previously described for these organisms.

Differential characteristics of catalase-positive campylobacters correlated with DNA homology groups

Eighty-four strains of catalase-positive campylobacters could be placed into seven distinct DNA homology groups (species), corresponding to Campylobacter fetus, "C. hyointestinalis," C. jejuni, C. coli, "C. laridis," "C. fecalis," and aerotolerant campylobacters. The biochemical and physiological characteristics of the strains were examined for their correlation with the homology groups. The characterization tests that provided the most reliable differentiation at the species and subspecies level were growth at 25 and 42 degrees C, sensitivity to cephalothin and nalidixic acid, growth in semisolid media containing 1% glycine and 3.5% NaCl, growth on plates containing 1.5% NaCl, growth in a semisolid minimal medium, anaerobic growth in the presence of 0.1% trimethylamine-N-oxide, hydrogen sulfide production in SIM medium and triple-sugar iron agar, hippurate hydrolysis, nitrite reduction, and growth on plates under an air atmosphere.