Identification of the virB operon genes encoding the type IV secretion system, in Colombian Brucella canis isolates

Prevalence and Genomic Characterization of Brucella canis Strains Isolated from Kennels, Household, and Stray Dogs in Chile

Canine brucellosis caused by Brucella canis is a zoonotic disease that causes reproductive alterations in dogs, such as infertility, abortion, and epididymitis. This pathogen is especially prevalent in South America, and due to the lack of official control programs and the growing trend of adopting dogs it constitutes a public health risk that must be addressed. The aim of this study was to determine the prevalence of B. canis infection in kennel, shelter, and household dogs and to characterize the genomic properties of circulating strains, including ure and virB operons and omp25/31 genes. Samples from 771 dogs were obtained, and the infection was detected by blood culture and/or serology in 7.0% of the animals. The complete ure and virB operons and the omp25/31 genes were detected. Interestingly, we found different single-nucleotide polymorphisms (SNPs) in some of the analyzed genes, which could mean a change in the fitness or virulence of these strains. This study provides further evidence about dogs as a source of B. canis strains that can infect people. This also highlights the need to implement official control programs, including the mandatory testing of dogs, especially stray dogs, before adoption.

Diagnosis of human and canine Brucella canis infection: development and evaluation of indirect enzyme-linked immunosorbent assays using recombinant Brucella proteins

Brucella canis, a Gram-negative coccobacilli belonging to the genus Brucellae, is a pathogenic bacterium that can produce infections in dogs and humans. Multiple studies have been carried out to develop diagnostic techniques to detect all zoonotic Brucellae. Diagnosis of Brucella canis infection is challenging due to the lack of highly specific and sensitive diagnostic assays. This work was divided in two phases: in the first one, were identified antigenic proteins in B. canis that could potentially be used for serological diagnosis of brucellosis. Human sera positive for canine brucellosis infection was used to recognize immunoreactive proteins that were then identified by performing 2D-GEL and immunoblot assays. These spots were analyzed using MALDI TOF MS and predicted proteins were identified. Of the 35 protein spots analyzed, 14 proteins were identified and subsequently characterized using bioinformatics, two of this were selected for the next phase. In the second phase, we developed and validated an indirect enzyme-linked immunosorbent assays using those recombinant proteins: inosine 5' phosphate dehydrogenase, pyruvate dehydrogenase E1 subunit beta (PdhB) and elongation factor Tu (Tuf). These genes were PCR-amplified from genomic DNA of B. canis strain Oliveri, cloned, and expressed in Escherichia coli. Recombinant proteins were purified by metal affinity chromatography, and used as antigens in indirect ELISA. Serum samples from healthy and B. canis-infected humans and dogs were used to evaluate the performance of indirect ELISAs. Our results suggest that PdhB and Tuf proteins could be used as antigens for serologic detection of B. canis infection in humans, but not in dogs. The use of recombinant antigens in iELISA assays to detect B. canis-specific antibodies in human serum could be a valuable tool to improve diagnosis of human brucellosis caused by B. canis.

Identification of Brucella abortus biovar 4 of bovine origin in Colombia

The objective of this study was to identify twelve Brucella abortus isolates of bovine origin from the department of Nariño in Colombia up to the biovar level. These isolates are included in the collection of the Germplasm Bank of Microorganisms of Animal Health Interest - Bacteria and Virus (BGSA-BV). The identification was carried out through conventional methods such as macro and microscopic morphological descriptions, enzymatic activity, biochemical profile, substrate use and sensitivity to dyes. Complementary genotypic characterization was carried out using multiplex PCR for B. abortus, Brucella melitensis, Brucella ovis, and Brucella suis-Erytritol (AMOS-ERY-PCR), RFLP-IS711, by southern blot hybridization, as well as by the multiple locus variable number of tandem repeat analysis (MLVA) using the ery gene and the insertion sequence IS711 and variable number of tandem repeats (VNTR) as molecular markers. The results of the phenotypic and molecular characterization allowed to identify twelve isolates as B. abortus biovar 4 as well as to differentiate field from vaccine strains. This is the first study on the phenotypic and molecular identification of B. abortus isolates in Colombia. It was concluded that the phenotypic and molecular identification of twelve isolates as B. abortus biovar 4 could be achieved using conventional and molecular techniques with enough resolution power. The identification of these isolates to the biovar level in taxonomic and epidemiological terms will allow the use of this genetic resource as reference strains in future research. This finding constitutes the basis for identifying biotypes not previously reported in the country that might be useful to support brucellosis survey programs in Colombia.

Genotyping Brucella canis isolates using a highly discriminatory multilocus variable-number tandem-repeat analysis (MLVA) assay

Differentiation of Brucella canis from other Brucella species are mainly performed through PCR-based methods and multilocus variable-number tandem-repeat (VNTR) analysis (MLVA) procedures. Both PCR-based and MLVA methods are limited in discriminating B. canis strains. A new MLVA-13Bc method for B. canis genotyping was established by combining eight newly-developed VNTRs with five published ones. During 2010 and 2016, 377 B. canis PCR-positives were identified from 6,844 canine blood samples from 22 U.S. states, resulting in 229 B. canis isolates. The MLVA-13Bc method was able to differentiate each of these 229 isolates. The Hunter-Gaston Discriminatory Index of the individual VNTR loci ranged from 0.516 to 0.934 and the combined discriminatory index reached 1.000. Three major clusters (A, B and C) and 10 genotype groups were identified from the 229 B. canis isolates. Cluster A mainly contains genotype groups 1 and 2, and a few group 3 isolates; nearly all Cluster B isolates were from group 6; other genotype groups were classified into Cluster C. Our newly developed MLVA-13Bc assay is a highly discriminatory assay for B. canis genotyping, and can serve as a useful molecular epidemiological tool, especially for tracing the source of contamination in an event of a B. canis outbreak.

Ecological Genomics of the Uncultivated Marine Roseobacter Lineage CHAB-I-5

Members of the marine Roseobacter clade are major participants in global carbon and sulfur cycles. While roseobacters are well represented in cultures, several abundant pelagic lineages, including SAG-O19, DC5-80-3, and NAC11-7, remain largely uncultivated and show evidence of genome streamlining. Here, we analyzed the partial genomes of three single cells affiliated with CHAB-I-5, another abundant but exclusively uncultivated Roseobacter lineage. Members of this lineage encode several metabolic potentials that are absent in streamlined genomes. Examples are quorum sensing and type VI secretion systems, which enable them to effectively interact with host and other bacteria. Further analysis of the CHAB-I-5 single-cell amplified genomes (SAGs) predicted that this lineage comprises members with relatively large genomes (4.1 to 4.4 Mbp) and a high fraction of noncoding DNA (10 to 12%), which is similar to what is observed in many cultured, nonstreamlined Roseobacter lineages. The four uncultured lineages, while exhibiting highly variable geographic distributions, together represent >60% of the global pelagic roseobacters. They are consistently enriched in genes encoding the capabilities of light harvesting, oxidation of "energy-rich" reduced sulfur compounds and methylated amines, uptake and catabolism of various carbohydrates and osmolytes, and consumption of abundant exudates from phytoplankton. These traits may define the global prevalence of the four lineages among marine bacterioplankton.

Immunization with Brucella VirB proteins reduces organ colonization in mice through a Th1-type immune response and elicits a similar immune response in dogs

VirB proteins from Brucella spp. constitute the type IV secretion system, a key virulence factor mediating the intracellular survival of these bacteria. Here, we assessed whether a Th1-type immune response against VirB proteins may protect mice from Brucella infection and whether this response can be induced in the dog, a natural host for Brucella. Splenocytes from mice immunized with VirB7 or VirB9 responded to their respective antigens with significant and specific production of gamma interferon (IFN-γ), whereas interleukin-4 (IL-4) was not detected. Thirty days after an intraperitoneal challenge with live Brucella abortus, the spleen load of bacteria was almost 1 log lower in mice immunized with VirB proteins than in unvaccinated animals. As colonization reduction seemed to correlate with a Th1-type immune response against VirB proteins, we decided to assess whether such a response could be elicited in the dog. Peripheral blood mononuclear cells (PBMCs) from dogs immunized with VirB proteins (three subcutaneous doses in QuilA adjuvant) produced significantly higher levels of IFN-γ than cells from control animals upon in vitro stimulation with VirB proteins. A skin test to assess specific delayed-type hypersensitivity was positive in 4 out of 5 dogs immunized with either VirB7 or VirB9. As both proteins are predicted to locate in the outer membrane of Brucella organisms, the ability of anti-VirB antibodies to mediate complement-dependent bacteriolysis of B. canis was assessed in vitro. Sera from dogs immunized with either VirB7 or VirB9, but not from those receiving phosphate-buffered saline (PBS), produced significant bacteriolysis. These results suggest that VirB-specific responses that reduce organ colonization by Brucella in mice can be also elicited in dogs.