Sequence and characterization of an insertion sequence, IS711, from Brucella ovis

Characterization of three predicted zinc exporters in Brucella ovis identifies ZntR-ZntA as a powerful zinc and cadmium efflux system not required for virulence and unveils pathogenic Brucellae heterogeneity in zinc homeostasis

Brucella ovis causes non-zoonotic ovine brucellosis of worldwide distribution and is responsible for important economic losses mainly derived from male genital lesions and reproductive fails. Studies about the virulence mechanisms of this rough species (lacking lipopolysaccharide O-chains) are underrepresented when compared to the main zoonotic Brucella species that are smooth (with O-chains). Zinc intoxication constitutes a defense mechanism of the host against bacterial pathogens, which have developed efflux systems to counterbalance toxicity. In this study, we have characterized three potential B. ovis zinc exporters, including the ZntA ortholog previously studied in B. abortus. Despite an in-frame deletion removing 100 amino acids from B. ovis ZntA, the protein retained strong zinc efflux properties. Only indirect evidence suggested a higher exporter activity for B. abortus ZntA, which, together with differences in ZntR-mediated regulation of zntA expression between B. ovis and B. abortus, could contribute to explaining why the ΔzntR mutant of B. abortus is attenuated while that of B. ovis is virulent. Additionally, B. ovis ZntA was revealed as a powerful cadmium exporter contributing to cobalt, copper, and nickel detoxification, properties not previously described for the B. abortus ortholog. Deletion mutants for BOV_0501 and BOV_A1100, also identified as potential zinc exporters and pseudogenes in B. abortus, behaved as the B. ovis parental strain in all tests performed. However, their overexpression in the ΔzntA mutant allowed the detection of discrete zinc and cobalt efflux activity for BOV_0501 and BOV_A1100, respectively. Nevertheless, considering their low expression levels and the stronger activity of ZntA as a zinc and cobalt exporter, the biological role of BOV_0501 and BOV_A1100 is questionable. Results presented in this study evidence heterogeneity among pathogenic Brucellae regarding zinc export and, considering the virulence of B. ovis ΔzntA, suggest that host-mediated zinc intoxication is not a relevant mechanism to control B. ovis infection.

Genomic distribution of the insertion sequence IS711 reveal a potential role in Brucella genome plasticity and host preference

The Insertion Sequence 711 (IS711) is linked to the Brucella genus. Mapping the genomic distribution of IS711 can help understand this insertion element's biological and evolutionary role. This work aimed to delineate the genomic distribution of the IS711 element and to study its association with Brucella evolution. A total of 124 genomes representing 9 Brucella species were searched using BLASTn sequence alignment tool to identify complete and truncated copies of IS711. Based on the genomic context, each IS711 locus was assigned a code using the initial letters of its neighboring genes. Various tools were used to annotate the neighboring genes and determine the shared synteny around orthologous IS711 loci. The tool Islandviewer 4 was used to scan for genomic islands. The Codon Tree method was used to build phylogenetic trees of B. melitensis, B. abortus, and B. suis genomes. The phylogenetic trees of the three species were analyzed, taking into account the genomic distribution patterns of IS711. The result of IS711 frequency analysis showed a relatively conserved number of copies/genome for the different species and for some biovars. The analysis showed that Brucella species with a relatively low IS711 copy number (4-8 copies/genome) are linked to domestic animals as primary hosts and have potential for zoonotic transmission. However, species with a relatively higher copy number (12-30 copies/genome) are less zoonotic and tend to be linked with wild animals as primary hosts. Analyzing the genomic distribution map of IS711 loci showed several unique patterns of IS711 distribution that are correlated with the evolution of Brucella species and biovars. The results also showed that 46.2% of the conserved IS711 elements are located within genomic islands. Based on our results and previous data, we postulate a model explaining the IS711 role in Brucella evolution. We assume that during the transition from a free-living to an intracellular lifestyle, a descendant of the Brucella genus had acquired a progenitor sequence of the IS711. Subsequently, a burst in IS711 transposition occurred. This parasitic expansion can be deleterious and has to be counteracted by evolutionary forces to prevent lineage extension and to promote adaptation to host. Similar to other plasmid-free pathogenic α-Proteobacteria bacteria, the balance of expansion and reduction of insertion elements could be one of the mechanisms to control genome reduction and streamlining. We hypothesize that the IS711-mediated genomic changes and other small sequence nucleotide changes in specific orthologous genes could significantly contribute to Brucella's evolution and adaptation to different animal hosts.

Molecular characterization of Brucella spp. from seropositive herds of cattle farmed at the wildlife-livestock-human interface in Rwanda

Seroprevalence studies showed that brucellosis is prevalent in cattle in Rwanda with no recent study on the characterization of Brucella spp. Therefore, this study aimed to characterize Brucella spp. in seropositive herds of cattle farmed at the wildlife–livestock–human interface. Whole blood samples (n = 118), milk (n = 41), and vaginal swabs (n = 51) were collected from 64 seropositive herds. All samples (n = 210) were inoculated onto modified Centro de Investigacion y Tecnologia Agroalimentaria (CITA) selective medium. Cultures were analyzed to detect Brucella spp. using 16S−23S ribosomal DNA interspacer region (ITS) PCR, the Brucella cultures were speciated using AMOS and Bruce-ladder PCR assays. Brucella spp. were detected in 16.7% (35/210) of the samples established from the samples using ITS-PCR. The AMOS PCR assay identified mixed Brucella abortus and B. melitensis (n = 6), B. abortus (n = 7), and B. melitensis (n = 1) from cultures from blood samples; mixed B. abortus and B. melitensis (n = 1) and B. abortus (n = 4) from cultures from milk samples; mixed B. abortus and B. melitensis (n = 6), B. abortus (n = 8), and B. melitensis (n = 1) from cultures from vaginal swabs. Bruce-ladder PCR assay confirmed B. abortus and B. melitensis cultures. The isolation of Brucella spp. was significantly associated with districts, with the Nyagatare district having more isolates than other districts (p = 0.01). This study identified single or mixed B. abortus and B. melitensis infections in cattle samples in Rwanda, which emphasizes the need to improve brucellosis control at the wildlife–livestock–human interface and raise the awareness of cattle keepers, abattoir workers, laboratory personnel, and consumers of cattle products.

Animal Brucellosis: Seropositivity rates, Isolation and Molecular Detection in Southern and Central Ethiopia

INTRODUCTION

Brucellosis is a neglected bacterial zoonosis with serious veterinary and public health importance throughout the world. A cross-sectional study on animal brucellosis was conducted aiming to estimate seroprevalence and molecular detection.

METHODS

Blood samples were collected from a total of 4274 individual animals (cattle, small ruminants and camel) from 241 herds/flocks for serology and PCR. Serum samples were tested using multispecies I-ELISA. Blood clots from seropositive animals were also tested for brucellosis via PCR. Additionally, 13 vaginal swab samples were collected from animals (2 from bovine and 11 from small ruminants) with recent abortion history for bacterial isolation and molecular detection.

RESULTS

The overall individual animal and herd level seroprevalence was 3.95% (169/4274) and 18.26% (44/241) respectively. The animal level seroprevalence at species level was 1.58% (47/2982), 8.89% (97/1091) and 12.44% (25/201) in bovine, small ruminants (sheep and goat) and camel, respectively. Herd level seroprevalence were 5.43% (10/184), 52.08% (25/48) and 100% (9/9) in bovine, small ruminant and camel, respectively. The animal level seroprevalence of bovine from intensive and extensive systems was 1.10% (31/2808) and 2.87% (5/174) respectively. Blood clots tested for brucellosis via PCR were negative by RT-PCR. Brucella species was isolated from 6/13 (46.15%) vaginal swab samples cultured on Brucella selective agar, and shown to be B. melitensis using Real-Time PCR.

CONCLUSION

Overall, seropositivity for camels was higher than what has been reported previously. Also, there was a notable difference in this study in cattle seroprevalence when comparing extensive with intensive systems, with the extensive system having much greater seropositivity.

Ultrasensitive Detection of Pathogenic Bacteria by Targeting High Copy Signature Genes

Bacterial load in clinical samples is relatively low and difficult to detect. Improvements in assay sensitivity will greatly reduce false negative results and contribute to more accurate diagnoses. In the present study, we present a new strategy to improve the sensitivity of a nucleic acid assay by detecting the presence of a multi-copy gene. By using Brucella as a test model, we screened the genome and identified IS711 as a multiple copy gene. Distribution analysis of insertion sequence IS711 among different species and strains showed that each of the strains have 5 to 13 copies of IS711. Compared with the BMEI1001, BMEI0775 and BMEI0027, the assays of high copy genes IS711 showed higher sensitivity and is an ideal high copy signature gene for Brucella. Detection of clinical samples with assays targeting the signature genes showed that IS711 exist in higher concentrations than BMEI1001, BMEI0775 and BMEI0027. In addition, IS711 assay is more sensitive than other signature genes assay. Analysis of several other pathogenic bacteria successfully identified high copy number genes that could be used as signature genes. Therefore, this strategy of targeting high copy signature genes represents a universal strategy for the ultrasensitive detection of bacteria.

The Retrospective on Atypical Brucella Species Leads to Novel Definitions

The genus Brucella currently comprises twelve species of facultative intracellular bacteria with variable zoonotic potential. Six of them have been considered as classical, causing brucellosis in terrestrial mammalian hosts, with two species originated from marine mammals. In the past fifteen years, field research as well as improved pathogen detection and typing have allowed the identification of four new species, namely Brucella microti, Brucella inopinata, Brucella papionis, Brucella vulpis, and of numerous strains, isolated from a wide range of hosts, including for the first time cold-blooded animals. While their genome sequences are still highly similar to those of classical strains, some of them are characterized by atypical phenotypes such as higher growth rate, increased resistance to acid stress, motility, and lethality in the murine infection model. In our review, we provide an overview of state-of-the-art knowledge about these novel Brucella sp., with emphasis on their phylogenetic positions in the genus, their metabolic characteristics, acid stress resistance mechanisms, and their behavior in well-established in cellulo and in vivo infection models. Comparison of phylogenetic classification and phenotypical properties between classical and novel Brucella species and strains finally lead us to propose a more adapted terminology, distinguishing between core and non-core, and typical versus atypical brucellae, respectively.

Brucella ceti sequence type 23, 26, and 27 infections in North American cetaceans

Brucella ceti infection is associated with a variety of disease outcomes in cetaceans globally. Multiple genotypes of B. ceti have been identified. This retrospective aimed to determine if specific lesions were associated with different B. ceti DNA sequence types (STs). Characterization of ST was performed on 163 samples from 88 free-ranging cetaceans, including common bottlenose dolphin Tursiops truncatus (T.t.; n = 73), common short-beaked dolphin Delphinus delphis (D.d.; n = 7), striped dolphin Stenella coeruleoalba (n = 3), Pacific white-sided dolphin Lagenorhynchus obliquidens (n = 2), sperm whale Physeter macrocephalus (n = 2), and harbour porpoise Phocoena phocoena (n = 1), that stranded along the coast of the US mainland and Hawaii. ST was determined using a previously described insertion sequence 711 quantitative PCR. Concordance with 9-locus multi-locus sequence typing was assessed in a subset of samples (n = 18). ST 26 was most commonly identified in adult dolphins along the US east coast with non-suppurative meningoencephalitis (p = 0.009). Animals infected with ST 27 were predominately perinates that were aborted or died shortly after birth with evidence of in utero pneumonia (p = 0.035). Reproductive tract inflammation and meningoencephalitis were also observed in adult T.t. and D.d. with ST 27, though low sample size limited interpretation. ST 23 infections can cause disease in cetacean families other than porpoises (Phocoenidae), including neurobrucellosis in D.d. In total, 11 animals were potentially infected with multiple STs. These data indicate differences in pathogenesis among B. ceti STs in free-ranging cetaceans, and infection with multiple STs is possible.

Brucella Genomics: Macro and Micro Evolution

Brucella organisms are responsible for one of the most widespread bacterial zoonoses, named brucellosis. The disease affects several species of animals, including humans. One of the most intriguing aspects of the brucellae is that the various species show a ~97% similarity at the genome level. Still, the distinct Brucella species display different host preferences, zoonotic risk, and virulence. After 133 years of research, there are many aspects of the Brucella biology that remain poorly understood, such as host adaptation and virulence mechanisms. A strategy to understand these characteristics focuses on the relationship between the genomic diversity and host preference of the various Brucella species. Pseudogenization, genome reduction, single nucleotide polymorphism variation, number of tandem repeats, and mobile genetic elements are unveiled markers for host adaptation and virulence. Understanding the mechanisms of genome variability in the Brucella genus is relevant to comprehend the emergence of pathogens.

Validation of real-time PCR technique for detection of Mycobacterium bovis and Brucella abortus in bovine raw milk

Brucellosis and tuberculosis are diseases of great economic impact in cattle herds and are controlled by governmental programs in many countries. The validation of a diagnostic technique is fundamental for its application in official control programs of these diseases. The aim of the present study was to validate a polymerase chain reaction in real time (qPCR) for detection of Mycobacterium bovis and Brucella abortus in samples of artificially contaminated raw milk. The technique was evaluated using tests of analytical sensitivity and specificity, repeatability, internal reproducibility, and robustness. Initially, five DNA extraction methodologies were tested, and the DNeasy Mericon Food Kit-Qiagen and the Maxwell® 16 Tissue DNA Purification Kit-Promega presented the best analytical specificity of all the commercial kits tested and were used exclusively in subsequent tests. The lowest limits of detection obtained in the qPCR were 2.3 pg for M. bovis DNA and 20.7 fg for B. abortus DNA. The repeatability and reproducibility associated with the robustness indicate that the evaluated methods are applicable as rapid tools for the official in vivo diagnosis of bovine tuberculosis and brucellosis in raw milk from dairy herds in Brazil.

Evaluation of real-time PCR as an alternative for potency testing of Brucella abortus vaccines

The aim of the research was to evaluate real-time PCR (qPCR) as an alternate method for quantitative detection of Brucella abortus strain 544 (S544) in the spleen of mice for potency testing of live B. abortus strain 19 (S19) vaccine. IS711 and eryC gene-based qPCR were optimized for calculating copy number. The copy number was further correlated with live Brucella count in the spleen by standard plate count (SPC) method. The mice were immunized with S19 and challenged with S544 on 30th Day post-immunization. The spleen of mice was collected at 15th, 21st, and 30th days post challenge (DPC) for estimation of S19 and S544 load via SPC as well as qPCR. The noteworthy difference was observed between immunized and unimmunized group by both methods at all time points. The maximum correlation between SPC and qPCR method was observed at 15th DPC in both immunized and unimmunized group. Repeated experiments at 15th DPC gave the parallel significant difference between immunized and unimmunized group by both methods. Thus novel, risk-free qPCR method can be used for the indirect culture-free potency evaluation of S19 vaccine in order to preclude the cultivation of zoonotic Brucella organisms from spleen samples.

Genome-scale approach to study the genetic relatedness among Brucella melitensis strains

Brucellosis is an important zoonotic disease that affects both humans and animals. To date, laboratory surveillance is still essentially based on the traditional MLVA-16 methodology and the associated epidemiological information is frequently scarce. Our goal was to contribute to the improvement of Brucella spp. surveillance through the implementation of a whole genome sequencing (WGS) approach. We created a curated ready-to-use species-specific wgMLST scheme enrolling a panel of 2656 targets (http://doi.org/10.5281/zenodo.3575026) and used this schema to perform a retrospective analysis of the genetic relatedness among B. melitensis strains causing human infection in Portugal (a country where brucellosis is an endemic disease) from 2010 to 2018. The strains showed a phylogenetic clustering within genotype II (25 out of 36) and IV (4 out of 36), and shared clades with strains isolated from countries with which Portugal has intense food trading, tourism and similar eating habits, such as Spain, Italy and Greece. In addition, our results point to the identification of strong associations between B. melitensis strains, likely underlying missed "outbreaks" as 22 out of the 36 strains showed genetic linkage with others. In fact, the applied gene-by-gene approach grouped these strains into six genetic clusters each one containing putative epidemiological links. Nevertheless, more studies will be needed in order to define the appropriate range of cut-offs (probable non-static cut-offs) that best illustrate the association between genetic linkage and epidemiological information and may serve as alerts for the health authorities. The release of this freely available and scalable schema contributes to the required technological transition for laboratorial surveillance of brucellosis and will facilitate the assessment of ongoing and future outbreaks in order to prevent the transmission spread.

Monitoring the course of Brucella infection with qPCR-based detection

OBJECTIVES

To determine blood Brucella DNA loads between brucellosis patients and those without brucellosis.

METHODS

The patient group included 350 brucellosis patients. The control was composed of 200 subjects without brucellosis. The extracted DNA from blood was tested by quantitative polymerase chain reaction (qPCR). The cutoff value was determined by receiver operating characteristic curve analysis. A portion of the brucellosis patients were monitored by qPCR during therapy.

RESULTS

The detection limit of qPCR was between 1E+01cfu/μL and 1E+08cfu/μL. The standard curve R² reached 0.998. The cutoff value was 4E+01cfu/μL, which was determined by comparison of the patient group and the control. The qPCR assay had a specificity of 100% and a sensitivity of 93.14%. The monitoring results showed that the Brucella DNA load decreased in most patients during the first 4 weeks of treatment. One patient with bad treatment compliance showed a rebound.

CONCLUSIONS

The qPCR results were in accordance with the course of brucellosis in the clinic. The DNA load often reflects the situation of the Brucella-infected patient. The cutoff value provides an important reference of infection. This qPCR-based method can be used to assist in the diagnosis of brucellosis and to adjust the therapy.

Detection of Brucella spp. in milk from seronegative cows by real-time polymerase chain reaction in the region of Batna, Algeria

Aim:

The aim of this study was to detect Brucella spp. DNA in milk samples collected from seronegative cows using the real-time polymerase chain reaction (PCR) assay for diagnosis of brucellosis in seronegative dairy cows to prevent transmission of disease to humans and to reduce economic losses in animal production.

Materials and Methods:

In this study, 65 milk samples were investigated for the detection of Brucella spp. The detection of the IS711 gene in all samples was done by real-time PCR assay by comparative cycle threshold method.

Results:

The results show that of the 65 DNA samples tested, 2 (3.08%) were positive for Brucella infection. The mean cyclic threshold values of IS711 real-time PCR test were 37.97 and 40.48, indicating a positive reaction.

Conclusion:

The results of the present study indicated that the real-time PCR appears to offer several advantages over serological tests. For this reason, the real-time PCR should be validated on representative numbers of Brucella-infected and free samples before being implemented in routine diagnosis in human and animal brucellosis for controlling this disease.

Survey of Parasitic Bacteria in Bat Bugs, Colorado

Bat bugs (Cimex adjunctus Barber) (Hemiptera: Cimicidae) collected from big brown bats (Eptesicus fuscus Palisot de Beauvoir) in Colorado, United States were assessed for the presence of Bartonella, Brucella, and Yersinia spp. using molecular techniques. No evidence of Brucella or Yersinia infection was found in the 55 specimens collected; however, 4/55 (7.3%) of the specimens were positive for Bartonella DNA. Multi-locus characterization of Bartonella DNA shows that sequences in bat bugs are phylogenetically related to other Bartonella isolates and sequences from European bats.

Isolation & characterization of Brucella melitensis isolated from patients suspected for human brucellosis in India

Background & objectives:

Brucellosis is endemic in the southern part of India. A combination of biochemical, serological and molecular methods is required for identification and biotyping of Brucella. The present study describes the isolation and biochemical, molecular characterization of Brucella melitensis from patients suspected for human brucellosis.

Methods:

The blood samples were collected from febrile patients suspected to have brucellosis. A total of 18 isolates were obtained from 102 blood samples subjected to culture. The characterization of these 18 isolates was done by growth on Brucella specific medium, biochemical reactions, CO₂ requirement, H₂S production, agglutination with A and M mono-specific antiserum, dye sensitivity to basic fuchsin and thionin. Further, molecular characterization of the isolates was done by amplification of B. melitensis species specific IS711 repetitive DNA fragment and 16S (rRNA) sequence analysis. PCR-restriction fragment length polymorphism (RFLP) analysis of omp2 locus and IS711 gene was also done for molecular characterization.

Results:

All 102 suspected samples were subjected to bacteria isolation and of these, 18 isolates could be recovered on blood culture. The biochemical, PCR and PCR-RFLP and 16s rRNA sequencing revealed that all isolates were of B. melitensis and matched exactly with reference strain B. melitensis 16M.

Interpretation & conclusions:

The present study showed an overall isolation rate of 17.64 per cent for B. melitensis. There is a need to establish facilities for isolation and characterization of Brucella species for effective clinical management of the disease among patients as well as surveillance and control of infection in domestic animals. Further studies are needed from different geographical areas of the country with different level of endemicity to plan and execute control strategies against human brucellosis.

Molecular Survey of Bacterial Zoonotic Agents in Bats from the Country of Georgia (Caucasus)

Bats are important reservoirs for many zoonotic pathogens. However, no surveys of bacterial pathogens in bats have been performed in the Caucasus region. To understand the occurrence and distribution of bacterial infections in these mammals, 218 bats belonging to eight species collected from four regions of Georgia were examined for Bartonella, Brucella, Leptospira, and Yersinia using molecular approaches. Bartonella DNA was detected in 77 (35%) bats from all eight species and was distributed in all four regions. The prevalence ranged 6–50% per bat species. The Bartonella DNA represented 25 unique genetic variants that clustered into 21 lineages. Brucella DNA was detected in two Miniopterus schreibersii bats and in two Myotis blythii bats, all of which were from Imereti (west-central region). Leptospira DNA was detected in 25 (13%) bats that included four M. schreibersii bats and 21 M. blythii bats collected from two regions. The Leptospira sequences represented five genetic variants with one of them being closely related to the zoonotic pathogen L. interrogans (98.6% genetic identity). No Yersinia DNA was detected in the bats. Mixed infections were observed in several cases. One M. blythii bat and one M. schreibersii bat were co-infected with Bartonella, Brucella, and Leptospira; one M. blythii bat and one M. schreibersii bat were co-infected with Bartonella and Brucella; 15 M. blythii bats and three M. schreibersii bats were co-infected with Bartonella and Leptospira. Our results suggest that bats in Georgia are exposed to multiple bacterial infections. Further studies are needed to evaluate pathogenicity of these agents to bats and their zoonotic potential.

Brucella abortus is Prevalent in Both Humans and Animals in Bangladesh

To determine the role of different Brucella (B.) spp. in Bangladesh, 62 animal samples and 500 human sera were tested. Animal samples from cattle, goats and sheep (including milk, bull semen, vaginal swabs and placentas) were cultured for Brucella spp. Three test-positive human sera and all animal samples were screened by Brucella genus-specific real-time PCR (RT-PCR), and positive samples were then tested by IS711 RT-PCR to detect B. abortus and B. melitensis DNA. Only B. abortus DNA was amplified from 13 human and six animal samples. This is the first report describing B. abortus as the aetiological agent of brucellosis in occupationally exposed humans in Bangladesh. Of note is failure to detect B. melitensis DNA, the species most often associated with human brucellosis worldwide. Further studies are required to explore the occurrence of Brucella melitensis in Bangladesh.

Brucella papionis sp. nov., isolated from baboons (Papio spp.)

Two Gram-negative, non-motile, non-spore-forming coccoid bacteria (strains F8/08-60(T) and F8/08-61) isolated from clinical specimens obtained from baboons (Papio spp.) that had delivered stillborn offspring were subjected to a polyphasic taxonomic study. On the basis of 16S rRNA gene sequence similarities, both strains, which possessed identical sequences, were assigned to the genus Brucella. This placement was confirmed by extended multilocus sequence analysis (MLSA), where both strains possessed identical sequences, and whole-genome sequencing of a representative isolate. All of the above analyses suggested that the two strains represent a novel lineage within the genus Brucella. The strains also possessed a unique profile when subjected to the phenotyping approach classically used to separate species of the genus Brucella, reacting only with Brucella A monospecific antiserum, being sensitive to the dyes thionin and fuchsin, being lysed by bacteriophage Wb, Bk2 and Fi phage at routine test dilution (RTD) but only partially sensitive to bacteriophage Tb, and with no requirement for CO2 and no production of H2S but strong urease activity. Biochemical profiling revealed a pattern of enzyme activity and metabolic capabilities distinct from existing species of the genus Brucella. Molecular analysis of the omp2 locus genes showed that both strains had a novel combination of two highly similar omp2b gene copies. The two strains shared a unique fingerprint profile of the multiple-copy Brucella-specific element IS711. Like MLSA, a multilocus variable number of tandem repeat analysis (MLVA) showed that the isolates clustered together very closely, but represent a distinct group within the genus Brucella. Isolates F8/08-60(T) and F8/08-61 could be distinguished clearly from all known species of the genus Brucella and their biovars by both phenotypic and molecular properties. Therefore, by applying the species concept for the genus Brucella suggested by the ICSP Subcommittee on the Taxonomy of Brucella, they represent a novel species within the genus Brucella, for which the name Brucella papionis sp. nov. is proposed, with the type strain F8/08-60(T) ( = NCTC 13660(T) = CIRMBP 0958(T)).

Natural IS711 insertion causing omp31 gene inactivation in Brucella ovis

The present report describes an atypical Brucella ovis strain (Bo10) isolated from the epididymis and testis of an infected ram. Macroscopic and microscopic lesions characteristic for the infection, including positive Brucella immunostaining, were observed within lesions in the genital organs. Compared to other isolates, strain Bo10 required an additional day (a total of 96 hr) of incubation to form visible colonies, showed a distinct carbon source utilization profile, agglutinated only weakly with rough (R) serum, but showed a high capacity for autoagglutination. Isolate Bo10 failed to produce the 1,071-bp fragment in the outer membrane protein (omp) 31 gene-based part of the "Bruce-ladder" multiplex polymerase chain reaction system but did produce a 1,915-bp amplicon, thus presenting a profile similar to Brucella abortus. Sequence analysis of the 1,915-bp fragment revealed an 842-bp long insertion sequence (IS)711 transposon element inserted into the promoter region of the omp31 gene, immediately upstream from the ribosome binding site (-10 box/Pribnow box). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of a whole-cell lysate showed the absence in Bo10 of the approximately 31-kDa protein fragment associated with omp31. The results demonstrate a natural inactivation of omp31 and, consequently, the absence of the Omp31 protein in this B. ovis isolate. The novel location of IS711 within the genome of a naturally occurring B. ovis strain supports the hypothesis that IS711 could be an active transposon in this Brucella species.

Improved variation calling via an iterative backbone remapping and local assembly method for bacterial genomes

Sequencing data analysis remains limiting and problematic, especially for low complexity repeat sequences and transposon elements due to inherent sequencing errors and short sequence read lengths. We have developed a program, ReviSeq, which uses a hybrid method composed of iterative remapping and local assembly upon a bacterial sequence backbone. Application of this method to six Brucella suis field isolates compared to the newly revised B. suis 1330 reference genome identified on average 13, 15, 19 and 9 more variants per sample than STAMPY/SAMtools, BWA/SAMtools, iCORN and BWA/PINDEL pipelines, and excluded on average 4, 2, 3 and 19 variants per sample, respectively. In total, using this iterative approach, we identified on average 87 variants including SNVs, short INDELs and long INDELs per strain when compared to the reference. Our program outperforms other methods especially for long INDEL calling. The program is available at http://reviseq.sourceforge.net.

Brucella ceti and brucellosis in cetaceans

Since the first case of brucellosis detected in a dolphin aborted fetus, an increasing number of Brucella ceti isolates has been reported in members of the two suborders of cetaceans: Mysticeti and Odontoceti. Serological surveys have shown that cetacean brucellosis may be distributed worldwide in the oceans. Although all B. ceti isolates have been included within the same species, three different groups have been recognized according to their preferred host, bacteriological properties, and distinct genetic traits: B. ceti dolphin type, B. ceti porpoise type, and B. ceti human type. It seems that B. ceti porpoise type is more closely related to B. ceti human isolates and B. pinnipedialis group, while B. ceti dolphin type seems ancestral to them. Based on comparative phylogenetic analysis, it is feasible that the B. ceti ancestor radiated in a terrestrial artiodactyl host close to the Raoellidae family about 58 million years ago. The more likely mode of transmission of B. ceti seems to be through sexual intercourse, maternal feeding, aborted fetuses, placental tissues, vertical transmission from mother to the fetus or through fish or helminth reservoirs. The B. ceti dolphin and porpoise types seem to display variable virulence in land animal models and low infectivity for humans. However, brucellosis in some dolphins and porpoises has been demonstrated to be a severe chronic disease, displaying significant clinical and pathological signs related to abortions, male infertility, neurobrucellosis, cardiopathies, bone and skin lesions, strandings, and death.

Seroprevalence and risk factors for brucellosis in a high-risk group of individuals in Bangladesh

Brucellosis is an occupational hazard of livestock farmers, dairy workers, veterinarians, slaughterhouse workers, and laboratory personnel, all of whom are considered to belong to the high-risk occupational group (HROG). A study was undertaken to determine the seroprevalence of brucellosis, identify risk factors associated with brucellosis seropositivity, and detect Brucella at genus level using real-time polymerase chain reaction (PCR) among people in the HROG in the Dhaka division of Bangladesh. A sample of 500 individuals from the HROG was collected from three districts of Dhaka division of Bangladesh. A multiple random effects logistic regression model was used to identify potential risk factors. Two types of real-time PCR methods were applied to detect Brucella genus-specific DNA using serum from seropositive patients. The prevalence of brucellosis based on the three tests was observed to be 4.4% based on a parallel interpretation. The results of the multiple random effects logistic regression analysis with random intercept for district revealed that the odds of brucellosis seropositivity among individuals who had been in contact with livestock for more than 26 years was about 14 times higher as compared to those who had less than 5 years of contact with livestock. In addition, when the contact was with goats, the odds of brucellosis seropositivity were about 60 times higher as compared to when contact was with cattle only. Noticeable variation in brucellosis seropositivity among humans within the three districts was noted. All of the 13 individuals who tested positive for the serological tests were also positive in two types of real-time PCR using the same serum samples. Livestock farmers of brucellosis positive herds had a significantly higher probability to be seropositive for brucellosis. The study emphasized that contact with livestock, especially goats, is a significant risk factor for the transmission of brucellosis among individuals in the HROG.

A review of Brucella infection in marine mammals, with special emphasis on Brucella pinnipedialis in the hooded seal (Cystophora cristata)

Brucella spp. were isolated from marine mammals for the first time in 1994. Two novel species were later included in the genus; Brucella ceti and Brucella pinnipedialis, with cetaceans and seals as their preferred hosts, respectively. Brucella spp. have since been isolated from a variety of marine mammals. Pathological changes, including lesions of the reproductive organs and associated abortions, have only been registered in cetaceans. The zoonotic potential differs among the marine mammal Brucella strains. Many techniques, both classical typing and molecular microbiology, have been utilised for characterisation of the marine mammal Brucella spp. and the change from the band-based approaches to the sequence-based approaches has greatly increased our knowledge about these strains. Several clusters have been identified within the B. ceti and B. pinnipedialis species, and multiple studies have shown that the hooded seal isolates differ from other pinniped isolates. We describe how different molecular methods have contributed to species identification and differentiation of B. ceti and B. pinnipedialis, with special emphasis on the hooded seal isolates. We further discuss the potential role of B. pinnipedialis for the declining Northwest Atlantic hooded seal population.

Identification of new IS711 insertion sites in Brucella abortus field isolates

BACKGROUND

Brucellosis is a zoonosis caused by Brucella spp., a group of highly homogeneous bacteria. The insertion sequence IS711 is characteristic of these bacteria, and occurs in variable numbers and positions, but always constant within a given species. This species-associated polymorphism is used in molecular typing and identification. Field isolates of B. abortus, the most common species infecting cattle, typically carry seven IS711 copies (one truncated). Thus far, IS711 transposition has only been shown in vitro and only for B. ovis and B. pinnipedialis, two species carrying a high number of IS711 copies, but never in other Brucella species, neither in vitro nor in field strains.

RESULTS

We found several B. abortus strains isolated from milk and aborted fetuses that carried additional IS711 copies in two hitherto undescribed insertion sites: one in an intergenic region near to the 3' end of a putative lactate permease gene and the other interrupting the sequence of a marR transcriptional regulator gene. Interestingly, the second type of insertion was identified in isolates obtained repeatedly from the same herd after successive brucellosis outbreaks, an observation that proves the stability and virulence of the new genotype under natural conditions. Sequence analyses revealed that the new copies probably resulted from the transposition of a single IS711 copy common to all Brucella species sequenced so far.

CONCLUSIONS

Our results show that the replicative transposition of IS711 can occur under field conditions. Therefore, it represents an active mechanism for the emergence of genetic diversity in B. abortus thus contributing to intra-species genetic polymorphism.

Nucleotide polymorphism-based single-tube test for robust molecular identification of all currently described Brucella species

Among the numerous molecular methods described during the last 20 years to identify Brucella, multiplexed amplification methods offer the cheapest and simplest technical solution for molecular identification. However, one disadvantage of such methods is their need to undergo technical revalidation each time a new marker is added to the system. Moreover, polymorphic markers cannot be assessed at the single-nucleotide level in these assays. Since new Brucella species are continuously being described, open methodologies able to accommodate new markers while preserving all other system parameters have an obvious advantage. We present a ligase chain reaction (LCR)-based method that simultaneously assesses multiple genetic markers at the single-nucleotide level. Most of the selected markers originate from a multilocus sequence typing (MLST) database that has been extensively validated on hundreds of different Brucella strains. When assayed on both reference and field strains, the method yields characteristic capillary electrophoresis profiles for each of the 10 Brucella species described to date and displays discriminatory potential below the species level for some. Since the LCR methodology is insensitive to interference resulting from the use of multiple oligonucleotides in a single mixture, the way is open for smooth future updates of the proposed system. Such updates are inevitable, given the pending description of new Brucella species.

The genome sequence of Brucella pinnipedialis B2/94 sheds light on the evolutionary history of the genus Brucella

Background

Since the discovery of the Malta fever agent, Brucella melitensis, in the 19th century, six terrestrial mammal-associated Brucella species were recognized over the next century. More recently the number of novel Brucella species has increased and among them, isolation of species B. pinnipedialis and B. ceti from marine mammals raised many questions about their origin as well as on the evolutionary history of the whole genus.

Results

We report here on the first complete genome sequence of a Brucella strain isolated from marine mammals, Brucella pinnipedialis strain B2/94. A whole gene-based phylogenetic analysis shows that five main groups of host-associated Brucella species rapidly diverged from a likely free-living ancestor close to the recently isolated B. microti. However, this tree lacks the resolution required to resolve the order of divergence of those groups. Comparative analyses focusing on a) genome segments unshared between B. microti and B. pinnipedialis, b) gene deletion/fusion events and c) positions and numbers of Brucella specific IS711 elements in the available Brucella genomes provided enough information to propose a branching order for those five groups.

Conclusions

In this study, it appears that the closest relatives of marine mammal Brucella sp. are B. ovis and Brucella sp. NVSL 07-0026 isolated from a baboon, followed by B. melitensis and B. abortus strains, and finally the group consisting of B. suis strains, including B. canis and the group consisting of the single B. neotomae species. We were not able, however, to resolve the order of divergence of the two latter groups.

Brucellosis at the animal/ecosystem/human interface at the beginning of the 21st century

Following the recent discovery of new Brucella strains from different animal species and from the environment, ten Brucella species are nowadays included in the genus Brucella. Although the intracellular trafficking of Brucella is well described, the strategies developed by Brucella to survive and multiply in phagocytic and non-phagocytic cells, particularly to access nutriments during its intracellular journey, are still largely unknown. Metabolism and virulence of Brucella are now considered to be two sides of the same coin. Mechanisms presiding to the colonization of the pregnant uterus in different animal species are not known. Vaccination is the cornerstone of control programs in livestock and although the S19, RB51 (both in cattle) and Rev 1 (in sheep and goats) vaccines have been successfully used worldwide, they have drawbacks and thus the ideal brucellosis vaccine is still very much awaited. There is no vaccine available for pigs and wildlife. Animal brucellosis control strategies differ in the developed and the developing world. Most emphasis is put on eradication and on risk analysis to avoid the re-introduction of Brucella in the developed world. Information related to the prevalence of brucellosis is still scarce in the developing world and control programs are rarely implemented. Since there is no vaccine available for humans, prevention of human brucellosis relies on its control in the animal reservoir. Brucella is also considered to be an agent to be used in bio- and agroterrorism attacks. At the animal/ecosystem/human interface it is critical to reduce opportunities for Brucella to jump host species as already seen in livestock, wildlife and humans. This task is a challenge for the future in terms of veterinary public health, as for wildlife and ecosystem managers and will need a "One Health" approach to be successful.

Rapid field detection assays for Bacillus anthracis, Brucella spp., Francisella tularensis and Yersinia pestis

Rapid detection is essential for timely initiation of medical post-exposure prophylactic measures in the event of intentional release of biological threat agents. We compared real-time PCR assay performance between the Applied Biosystems 7300/7500 and the RAZOR instruments for specific detection of the causative agents of anthrax, brucellosis, tularemia and plague. Furthermore, an assay detecting Bacillus thuringiensis, a Bacillus anthracis surrogate, was developed for field-training purposes. Assay sensitivities for B. anthracis, Brucella spp., Francisella tularensis and Yersinia pestis were 10-100 fg of target DNA per reaction, and no significant difference in assay performance was observed between the instrument platforms. Specificity testing of the diagnostic panels with both instrument platforms did not reveal any cross-reactivity with other closely related bacteria. The duration of thermocycling with the RAZOR instrument was shorter, i.e. 40 min as compared with 100 min for the Applied Biosystems 7300/7500 instruments. These assays provide rapid tools for the specific detection of four biological threat agents. The detection assays, as well as the training assay for B. thuringiensis powder preparation analysis, may be utilized under field conditions and for field training, respectively.

Medulloblastoma and Brucellosis - Molecular Evidence of Brucella sp in Association with Central Nervous System Cancer

Neurobrucellosis has been reported to cause lesions in a number of different locations in the central nervous system. Histologically or radiologically, these lesions were consistent with an infection. In response to parents who believed their child's brain tumor, histologically typical of medulloblastoma, was in reality neurobrucellosis, formalin-fixed paraffin-embedded tumor tissue from the medulloblastoma was sectioned, DNA extracted, and tested by polymerase chain reaction (PCR). Specific primer/probe sets, designed in our laboratory to target Brucella species, B. melitensis, B. abortus and B. suis, and designated OMP31, B-m, B-a and B-s, respectively, were used in TaqMan real-time PCR to amplify those gene targets in two separate blocks of the child's tumor. Sections from two blocks were positive only for Brucella species. Although the patient grew up in a European country known to harbor brucella in foods, such as unpasturized milk and cheese, the patient was seronegative for B. mellitensis, B. suis, and B. abortus. In an effort to test whether a relationship existed between the presence of brucella and medulloblastoma, 20 medulloblastomas were retrieved from the tissue repository of the AFIP. The above four primer/probe sets were again used to amplify brucella DNA. Five of 20 tumors (25%) contained Brucella species DNA by the OMP31 primer/probe set. None of the 20 medulloblastomas had specific sequences for B. mellitensis, B. suis, or B. abortus. Is chronic brucellosis similar to other infectious agents such as helicobacter that is associated with tumor formation?

Characterization of novel Brucella strains originating from wild native rodent species in North Queensland, Australia

We report on the characterization of a group of seven novel Brucella strains isolated in 1964 from three native rodent species in North Queensland, Australia, during a survey of wild animals. The strains were initially reported to be Brucella suis biovar 3 on the basis of microbiological test results. Our results indicated that the rodent strains had microbiological traits distinct from those of B. suis biovar 3 and all other Brucella spp. To reinvestigate these rodent strains, we sequenced the 16S rRNA, recA, and rpoB genes and nine housekeeping genes and also performed multiple-locus variable-number tandem-repeat (VNTR) analysis (MLVA). The rodent strains have a unique 16S rRNA gene sequence compared to the sequences of the classical Brucella spp. Sequence analysis of the recA, rpoB, and nine housekeeping genes reveals that the rodent strains are genetically identical to each other at these loci and divergent from any of the currently described Brucella sequence types. However, all seven of the rodent strains do exhibit distinctive allelic MLVA profiles, although none demonstrated an amplicon for VNTR 07, whereas the other Brucella spp. did. Phylogenetic analysis of the MLVA data reveals that the rodent strains form a distinct clade separate from the classical Brucella spp. Furthermore, whole-genome sequence comparison using the maximal unique exact matches index (MUMi) demonstrated a high degree of relatedness of one of the seven rodent Brucella strains (strain NF 2653) to another Australian rodent Brucella strain (strain 83-13). Our findings strongly suggest that this group of Brucella strains isolated from wild Australian rodents defines a new species in the Brucella genus.

Identification of an unusual Brucella strain (BO2) from a lung biopsy in a 52 year-old patient with chronic destructive pneumonia

Background

Brucellosis is primarily a zoonotic disease caused by Brucella species. There are currently ten Brucella spp. including the recently identified novel B. inopinata sp. isolated from a wound associated with a breast implant infection. In this study we report on the identification of an unusual Brucella-like strain (BO2) isolated from a lung biopsy in a 52-year-old patient in Australia with a clinical history of chronic destructive pneumonia.

Results

Standard biochemical profiles confirmed that the unusual strain was a member of the Brucella genus and the full-length 16S rRNA gene sequence was 100% identical to the recently identified B. inopinata sp. nov. (type strain BO1^T). Additional sequence analysis of the recA, omp2a and 2b genes; and multiple locus sequence analysis (MLSA) demonstrated that strain BO2 exhibited significant similarity to the B. inopinata sp. compared to any of the other Brucella or Ochrobactrum species. Genotyping based on multiple-locus variable-number tandem repeat analysis (MLVA) established that the BO2 and BO1^Tstrains form a distinct phylogenetic cluster separate from the other Brucella spp.

Conclusion

Based on these molecular and microbiological characterizations, we propose that the BO2 strain is a novel lineage of the newly described B. inopinata species.

Real-time PCR for identification of Brucella spp.: a comparative study of IS711, bcsp31 and per target genes

Culture is considered as the reference standard assay for diagnosis of Brucella spp. in humans and animals but it is time-consuming and hazardous. In this study, we evaluated the performances of newly designed real-time PCR assays using TaqMan probes and targeting the 3 following specific genes: (i) the insertion sequence IS711, (ii) bcsp31 and (iii) per genes for the detection of Brucella at genus level. The real-time PCR assays were compared to previously described conventional PCR assays targeting the same genes. The genus-specificity was evaluated on 26 Brucella strains, including all species and biovars. The analytical specificity was evaluated on a collection of 68 clinically relevant, phylogenetically related or serologically cross-reacting micro-organisms. The analytical sensitivity was assessed using decreasing DNA quantities of Brucella ovis, B. melitensis bv. 1, B. abortus bv. 1 and B. canis reference strains. Finally, intra-assay repeatability and inter-assay reproducibility were assessed. All Brucella species DNA were amplified in the three tests. However, the earliest signal was observed with the IS711 real-time PCR, where it varied according to the IS711 copy number. No cross-reactivity was observed in all three tests. Real-time PCR was always more sensitive than conventional PCR assays. The real-time PCR assay targeting IS711 presented an identical or a greater sensitivity than the two other tests. In all cases, the variability was very low. In conclusion, real-time PCR assays are easy-to-use, produce results faster than conventional PCR systems while reducing DNA contamination risks. The IS711-based real-time PCR assay is specific and highly sensitive and appears as an efficient and reproducible method for the rapid and safe detection of the genus Brucella.

Phenotypic and molecular characterisation of Brucella isolates from marine mammals

Background

Bacteria of the genus Brucella are the causative organisms of brucellosis in animals and man. Previous characterisation of Brucella strains originating from marine mammals showed them to be distinct from the terrestrial species and likely to comprise one or more new taxa. Recently two new species comprising Brucella isolates from marine mammals, B. pinnipedialis and B. ceti, were validly published. Here we report on an extensive study of the molecular and phenotypic characteristics of marine mammal Brucella isolates and on how these characteristics relate to the newly described species.

Results

In this study, 102 isolates of Brucella originating from eleven species of marine mammals were characterised. Results obtained by analysis using the Infrequent Restriction Site (IRS)-Derivative PCR, PCR-RFLP of outer membrane protein genes (omp) and IS711 fingerprint profiles showed good consistency with isolates originating from cetaceans, corresponding to B. ceti, falling into two clusters. These correspond to isolates with either dolphins or porpoises as their preferred host. Isolates originating predominantly from seals, and corresponding to B. pinnipedialis, cluster separately on the basis of IS711 fingerprinting and other molecular approaches and can be further subdivided, with isolates from hooded seals comprising a distinct group. There was little correlation between phenotypic characteristics used in classical Brucella biotyping and these groups.

Conclusion

Molecular approaches are clearly valuable in the division of marine mammal Brucella into subtypes that correlate with apparent ecological divisions, whereas conventional bioyping is of less value. The data presented here confirm that there are significant subtypes within the newly described marine mammal Brucella species and add to a body of evidence that could lead to the recognition of additional species or sub-species within this group.

Demonstration of IS711 transposition in Brucella ovis and Brucella pinnipedialis

Background

The Brucella genome contains an insertion sequence (IS) element called IS711 or IS6501, which is specific to the genus. The copy number of IS711 varies in the genome of the different Brucella species, ranging from 7 in B. abortus, B. melitensis and B. suis to more than 30 in B. ovis and in Brucella strains isolated from marine mammals. At present, there is no experimental evidence of transposition of IS711, but the occurrence of this element with a high copy number in some species, and the isolation of Brucella strains with "ectopic" copies of IS711 suggested that this IS could still transpose.

Results

In this study we obtained evidence of transposition of IS711 from the B. ovis and B. pinnipedialis chromosomes by using the "transposon trap" plasmid pGBG1. This plasmid expresses resistance to tetracycline only if the repressor gene that it contains is inactivated. The strains B. melitensis 16 M, B. abortus RB51, B. ovis BOC22 (field strain) and B. pinnipedialis B2/94, all containing the plasmid pGBG1, were grown in culture media with tetracycline until the appearance of tetracycline resistant mutants (Tc^R). Tc^R mutants due to IS711 transposition were only detected in B. ovis and B. pinnipedialis strains.

Conclusion

Four different copies of IS711 were found to transpose to the same target sequence in the plasmid pGBG1. This demonstrated that IS711 are active in vivo, specially in Brucella species with a high number of IS711 copies as B. ovis and B. pinnipedialis.

Novel Brucella strain (BO1) associated with a prosthetic breast implant infection

We report the microbiological, biochemical, and molecular characterization of an unusual Brucella strain (BO1) isolated from a breast implant wound in a 71-year-old woman with clinical symptoms consistent with brucellosis. Initial phenotypic analysis, including biochemical and antimicrobial susceptibility testing, cellular fatty acid analysis, and molecular analysis based on DNA-DNA reassociation and the presence of multiple copies of IS711 element suggested that the isolate was a Brucella-like organism, but species determination using microbiological algorithms was unsuccessful. Furthermore, molecular data based on 16S rRNA gene sequencing and multilocus sequence analysis demonstrated that BO1 was an unusual Brucella strain and not closely related to any currently described Brucella species. However, comparison with equivalent sequences in Ochrobactrum spp. confirms that the isolate is much more closely related to Brucella than to Ochrobactrum spp., and thus the isolate likely represents an atypical and novel strain within the genus Brucella.

Intrinsic and selected resistance to antibiotics binding the ribosome: analyses of Brucella 23S rrn, L4, L22, EF-Tu1, EF-Tu2, efflux and phylogenetic implications

Background

Brucella spp. are highly similar, having identical 16S RNA. However, they have important phenotypic differences such as differential susceptibility to antibiotics binding the ribosome. Neither the differential susceptibility nor its basis has been rigorously studied. Differences found among other conserved ribosomal loci could further define the relationships among the classical Brucella spp.

Results

Minimum inhibitory concentration (MIC) values of Brucella reference strains and three marine isolates to antibiotics binding the ribosome ranged from 0.032 to >256 μg/ml for the macrolides erythromycin, clarithromycin, and azithromycin and 2 to >256 μg/ml for the lincosamide, clindamycin. Though sequence polymorphisms were identified among ribosome associated loci 23S rrn, rplV, tuf-1 and tuf-2 but not rplD, they did not correlate with antibiotic resistance phenotypes. When spontaneous erythromycin resistant (ery^R) mutants were examined, mutation of the peptidyl transferase center (A2058G Ec) correlated with increased resistance to both erythromycin and clindamycin. Brucella efflux was examined as an alternative antibiotic resistance mechanism by use of the inhibitor L-phenylalanine-L-arginine β-naphthylamide (PAβN). Erythromycin MIC values of reference and all ery^R strains, except the B. suis ery^R mutants, were lowered variably by PAβN. A phylogenetic tree based on concatenated ribosomal associated loci supported separate evolutionary paths for B. abortus, B. melitensis, and B. suis/B. canis, clustering marine Brucella and B. neotomae with B. melitensis. Though Brucella ovis was clustered with B. abortus, the bootstrap value was low.

Conclusion

Polymorphisms among ribosomal loci from the reference Brucella do not correlate with their highly differential susceptibility to erythromycin. Efflux plays an important role in Brucella sensitivity to erythromycin. Polymorphisms identified among ribosome associated loci construct a robust phylogenetic tree supporting classical Brucella spp. designations.

Brucella abortus detection by PCR assay in blood, milk and lymph tissue of serologically positive cows

Brucellosis is a highly infectious disease which is diagnosed using serological and microbiological methods. The objective of this study was to assess the viability of using conventional and real-time PCR assays as potential diagnostic tools for the detection of Brucella abortus in naturally infected cows. PCR assays that amplify various regions of the Brucella genome, IS711 genetic element, 31kDa outer membrane protein and 16S rRNA, were optimised using nine known Brucella strains. Real-time PCR was used to examine the detection efficiency of the IS711 assay which was estimated at 10 gene copies. Milk, blood and lymph tissue samples were collected from naturally infected animals. B. abortus was not detected in blood samples collected from naturally infected cows by conventional or real-time PCR, but was detected in a proportion of the culture-positive milk (44%) and lymph tissue (66% - retropharyngeal, 75% - supramammary) samples by the same methods. There was no difference between PCR and bacteriological detection methods. It is unlikely that conventional or real-time PCR will supersede current diagnostic methods for detection of B. abortus in clinical samples.

Development of a new PCR assay to identify Brucella abortus biovars 5, 6 and 9 and the new subgroup 3b of biovar 3

One hundred twenty-nine Brucella field strains isolated from cattle in Cantabria, Spain, from March 1999 to February 2003, were analysed by using the AMOS-ERY PCR assay and by Southern blot hybridisation with a probe from insertion sequence IS711. Most of the field isolates produced only the ery band in the AMOS-ERY assay and showed a hybridisation pattern identical to that exhibited by reference strains of biovars 5, 6 and 9 of Brucella abortus, but different from strain Tulya, belonging to biovar 3 of B. abortus. However, typing of these strains by standard methods demonstrated that they belonged to biovar 3 of B. abortus. These results indicated that B. abortus biovar 3 was not genetically homogeneous and at least could be divided in two. In one class, that we called biovar 3a, would be the Tulya strain, while the local field strains would belong to biovar 3b. Cloning and nucleotide sequencing of a DNA fragment containing an IS711 copy exclusive of the B. abortus field strains from biovar 3b and reference strains from biovars 5, 6 and 9, revealed the existence of a 5.4 kb deletion close to an IS711 copy. Based on these data, we designed a new primer, which together with the IS711 AMOS primer produced a PCR fragment of 1.7 kb only from the isolates of biovars 3b, 5, 6 and 9 of B. abortus. No amplification products were produced with these primers from strains of the rest of species and biovars of Brucella and from bacteria phylogenetically close to Brucella analysed in this work. Addition of this primer to the AMOS-ERY PCR primer cocktail allows the positive distinction of B. abortus biovars 3b, 5, 6 and 9 from the rest of Brucella species and biovars.

Completion of the genome sequence of Brucella abortus and comparison to the highly similar genomes of Brucella melitensis and Brucella suis

Brucellosis is a worldwide disease of humans and livestock that is caused by a number of very closely related classical Brucella species in the alpha-2 subdivision of the Proteobacteria. We report the complete genome sequence of Brucella abortus field isolate 9-941 and compare it to those of Brucella suis 1330 and Brucella melitensis 16 M. The genomes of these Brucella species are strikingly similar, with nearly identical genetic content and gene organization. However, a number of insertion-deletion events and several polymorphic regions encoding putative outer membrane proteins were identified among the genomes. Several fragments previously identified as unique to either B. suis or B. melitensis were present in the B. abortus genome. Even though several fragments were shared between only B. abortus and B. suis, B. abortus shared more fragments and had fewer nucleotide polymorphisms with B. melitensis than B. suis. The complete genomic sequence of B. abortus provides an important resource for further investigations into determinants of the pathogenicity and virulence phenotypes of these bacteria.

Prevalence of Brucella pinnipediae in healthy hooded seals (Cystophora cristata) from the North Atlantic Ocean and ringed seals (Phoca hispida) from Svalbard

Investigations for Brucella-infections were conducted in 29 hooded seals (Cystophora cristata) caught between Svalbard and Greenland (North Atlantic Ocean; Greenland Sea) autumn 2002, and from 20 ringed seals (Phoca hispida) caught in Billefjord, Svalbard, spring 2003. All animals were apparently healthy and were caught in their natural habitat. Bacteriology on tissue samples from ringed seals was negative, whereas Brucella sp. were recovered in tissues from 11 of the 29 hooded seals (38%), with the highest tissue prevalence in spleen (9/29) and lung lymph nodes (9/24). Anti-Brucella antibodies were detected in sera from 9 hooded seals (31%) (EDTA-modified Slow Agglutination test of Wright, Rose Bengal test, Complement Fixation Test, and Protein-A ELISA). The bacterial isolates all belonged to the genus Brucella according to classical biotyping and PCR analysis based on Insertion Sequence IS711, and were shown to be typical marine mammal strains, based on the occurrence of an IS711 element downstream of the bp26 gene. Their dependency on CO2 for growth, and the presence of one copy each of the omp2a and omp2b gene finally classified them as Brucella pinnipediae. Furthermore, all the hooded seal isolates showed an A+ M+ agglutination profile, which is different from the profile of reference seal strain 2/94 (harbour seal, Phoca vitulina). Thus, these results indicate that B. pinnipediae may contain different biovars. The present results suggest that infection with B. pinnipediae is enzootic in this population. Since the hooded seal is commercially hunted and consumed in Norway, the pathological impact of such infections and their zoonotic potential should be further addressed.

Genetic diversity at alkB locus in Brucella abortus

DNA polymorphism of the alkB gene, a DNA repair gene, was assessed by PCR on Brucella abortus biovars 1 (strains 99, S19, 45/20, RB51 and 2308), 3 (Tulya strain), 5 (B3196 strain) and 6 (870 strain). A DNA repetitive element, named IS711, was detected in all studied biovars 1 and its complete nucleotide sequence was determined. We found that the element in alkB gene, bounded by 14 bp imperfect inverted repeats (IRs), is 840 bp long and appears to duplicate a consensus target site, CTAG. Analysing its nucleotide sequence of both forward and reverse strands, more than 10 open reading frames (ORFs) were found. Two potential transposase coding regions were chosen comparing all possible ORFs with the database. Comparing IS711 elements isolated from Brucella species, including both those characterized in our work and the published ones, differences in length and in nucleotide composition were observed among Brucella species, members of the same species and within the same strain. Our results confirm the heterogeneity of IS711 elements in Brucella genus and suggest the possibility to use this element to assess gene and genome diversity and to identify new molecular markers for Brucella species.

Classification of Brucella strains isolated from marine mammals by infrequent restriction site-PCR and development of specific PCR identification tests

Brucella strains have been isolated since the 1990s from a wide variety of marine mammals and represent potential zoonotic pathogens. They have distinctive phenotypic and molecular characteristics from the terrestrial mammal Brucella species, and two new species names have been previously proposed based on DNA polymorphism at the omp2 locus and their preferential host, i.e. Brucella cetaceae for cetacean isolates and Brucella pinnipediae for pinniped isolates. The results presented in this study on characterization of these strains by infrequent restriction site-PCR (IRS-PCR), taking into account the higher number of IS711 elements in their genome compared to terrestrial mammal Brucella species, supports this classification. The nucleotide sequences of specific DNA fragments detected by IRS-PCR were determined and used to develop PCR identification tests for either B. cetaceae or B. pinnipediae.

The Brucella genome at the beginning of the post-genomic era

The year 2002 began with the publication of the first complete genome sequence for a Brucella species, that of the two replicons of B. melitensis 16M. Hopefully in 2002, the complete genome of B. suis 1330, and, perhaps, a B. abortus strain will be published. This is the culmination of over 30 years investigation of the composition, structure, organisation and evolution of the Brucella genome. Brucella research must now adapt to the new challenges of the post-genomic era.

The genome of Brucella melitensis

The genome of Brucella melitensis strain 16M was sequenced and contained 3,294,931 bp distributed over two circular chromosomes. Chromosome I was composed of 2,117,144 bp and chromosome II has 1,177,787 bp. A total of 3,198 ORFs were predicted. The origins of replication of the chromosomes are similar to each other and to those of other alpha-proteobacteria. Housekeeping genes such as those that encode for DNA replication, protein synthesis, core metabolism, and cell-wall biosynthesis were found on both chromosomes. Genes encoding adhesins, invasins, and hemolysins were also identified.