Gene discovery through genomic sequencing of Brucella abortus

An Overview of Brucellosis in Cattle and Humans, and its Serological and Molecular Diagnosis in Control Strategies

Brucellosis is one of the most common contagious and communicable zoonotic diseases with high rates of morbidity and lifetime sterility. There has been a momentous increase over the recent years in intra/interspecific infection rates, due to poor management and limited resources, especially in developing countries. Abortion in the last trimester is a predominant sign, followed by reduced milk yield and high temperature in cattle, while in humans it is characterized by undulant fever, general malaise, and arthritis. While the clinical picture of brucellosis in humans and cattle is not clear and often misleading with the classical serological diagnosis, efforts have been made to overcome the limitations of current serological assays through the development of PCR-based diagnosis. Due to its complex nature, brucellosis remains a serious threat to public health and livestock in developing countries. In this review, we summarized the recent literature, significant advancements, and challenges in the treatment and vaccination against brucellosis, with a special focus on developing countries.

Comparative genomic analysis between newly sequenced Brucella suis Vaccine Strain S2 and the Virulent Brucella suis Strain 1330

Background

Brucellosis is a bacterial disease caused by Brucella infection. In the late fifties, Brucella suis vaccine strain S2 with reduced virulence was obtained by serial transfer of a virulent B. suis biovar 1 strain in China. It has been widely used for vaccination in China since 1971. Until now, the mechanisms underlie virulence attenuation of S2 are still unknown.

Results

In this paper, the whole genome sequencing of S2 was carried out by Illumina Hiseq2000 sequencing method. We further performed the comparative genomic analysis to find out the differences between S2 and the virulent Brucella suis strain 1330. We found premature stops in outer membrane autotransporter omaA and eryD genes. Single mutations were found in phosphatidylcholine synthase, phosphorglucosamine mutase, pyruvate kinase and FliF, which have been reported to be related to the virulence of Brucella or other bacteria. Of the other different proteins between S2 and 1330, such as Omp2b, periplasmic sugar-binding protein, and oligopeptide ABC transporter, no definitive implications related to bacterial virulence were found, which await further investigation.

Conclusions

The data presented here provided the rational basis for designing Brucella vaccines that could be used in other strains.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3076-5) contains supplementary material, which is available to authorized users.

Newly identified variability in Brucella canis fatty-acid content is associated with geographical origin

This study compared the fatty-acid profiles of Brucella canis blood culture isolates obtained from infected dogs in the UK, Germany, Japan, South Africa, Peru, Mexico, Colombia, and Argentina, and from a human clinical case in Argentina, to a bank of isolates obtained from canine outbreaks in the USA. Analysis of a total of 42 B. canis isolates and one reference strain found a marked variation within the species. Fatty-acid analysis showed that only the isolates from Argentina, Colombia, and Mexico, which included the human B. canis isolate, contained a specific fatty acid, 19:0 cyclopropane (lactobacillic acid), w8c (cis-11,12-methylene octadecanoic acid), and that this fatty acid, when present, made up a large percentage of overall fatty-acid content. Prior to this study, the cellular fatty-acid 19:0 cyclopropane had been identified in all of the species of Brucella considered to be pathogenic to humans (B. abortus, B. melitensis, B. suis) except for B. canis. Discovering that this fatty acid not only occurs in B. canis, but also that it is only present in some strains of the species provides a new focus for investigations aimed at identifying the cause of reported geographical variability in human B. canis infection, and at finding predictors of biological behaviour and human pathogenicity within this Brucella species.

Brucellosis: review on the recent trends in pathogenicity and laboratory diagnosis

Brucellosis is a zoonotic infection transmitted from animals to humans by the ingestion of infected food products, direct contact with an infected animal or inhalation of aerosols. The last method is remarkably efficient given the relatively low concentration of organisms (10 - 100 bacteria) needed to establish infection in humans, and has brought renewed attention to this old disease. Brucella is a facultative intracellular pathogen that has the ability to survive and multiply in the phagocytes and cause abortion in cattle and undulant fever in humans. Brucella spp particularly B. melitensis, B. abortus, and B. suis represent a significant public health concern. At present, B. melitensis is the principle cause of human brucellosis in India. Molecular studies have demonstrated the phylogenetic affiliation of Brucella to Agrobacterium, Ochrobactrum, and Rhizobium. Human brucellosis still presents scientists and clinicians with several challenges, with regard to the understanding of its pathogenic mechanism, severity, progression, and development of improved treatment regimens. Molecular studies have now highlighted the pathogenesis of Brucella, for the development of newer diagnostic tools that will be useful in developing countries where brucellosis is a common, but often a neglected disease. This review compiles all these issues in general and the pathogenicity and newer diagnostic tools in particular.

DeltaznuADeltapurE Brucella abortus 2308 mutant as a live vaccine candidate

To create a new, safe brucellosis live vaccine, a double mutant strain was constructed from Brucella abortus 2308. Using the DeltaznuA B. abortus 2308 mutant, a second mutation was introduced by deleting purE gene. The DeltaznuA DeltapurE B. abortus 2308 strain was less capable of surviving in macrophages. When evaluated in vivo, it was cleared within 8 weeks (wks) from mice, causing significantly less inflammation than spleens obtained from wild-type B. abortus 2308-infected mice. Furthermore, two doses of DeltaznuA DeltapurE B. abortus 2308 conferred 0.79 log protection, similar to S19 as did a single dose of DeltaznuA B. abortus 2308. Thus, this study shows the DeltaznuA DeltapurE B. abortus 2308 strain to be a potential livestock vaccine candidate.

Comparison of two multiple-locus variable-number tandem-repeat analysis methods for molecular strain typing of human Brucella melitensis isolates from the Middle East

Brucella species are highly monomorphic, with minimal genetic variation among species, hindering the development of reliable subtyping tools for epidemiologic and phylogenetic analyses. Our objective was to compare two distinct multiple-locus variable-number tandem-repeat analysis (MLVA) subtyping methods on a collection of 101 Brucella melitensis isolates from sporadic human cases of brucellosis in Egypt (n = 83), Qatar (n = 17), and Libya (n = 1). A gel-based MLVA technique, MLVA-15(IGM), was compared to an automated capillary electrophoresis-based method, MLVA-15(NAU), with each MLVA scheme examining a unique set of variable-number tandem repeats. Both the MLVA(IGM) and MLVA(NAU) methods were highly discriminatory, resolving 99 and 101 distinct genotypes, respectively, and were able to largely separate genotypes from Egypt and Qatar. The MLVA-15(NAU) scheme presented higher strain-to-strain diversity in our test population than that observed with the MLVA-15(IGM) assay. Both schemes were able to genetically correlate some strains originating from the same hospital or region within a country. In addition to comparing the genotyping abilities of these two schemes, we also compared the usability, limitations, and advantages of the two MLVA systems and their applications in the epidemiological genotyping of human B. melitensis strains.

Defense Against Biological Weapons (Biodefense)

Biological warfare (germ warfare) is defined as the use of any disease-causing organism or toxin(s) found in nature as weapons of war with the intent to destroy an adversary. Though rare, the use of biological weapons has occurred throughout the centuries.

In vitro and in vivo characterization of smooth small colony variants of Brucella abortus S19

Brucella abortus is known to produce chronic infections in both humans and a variety of animal species. However, the mechanisms underlying the persistence of the bacteria in the presence of an ongoing immune response are still unknown. In this respect we made use of the observation that in vitro grown B. abortus S19 exhibits heterogenicity in colony size when plated onto TS agar, while experimental infection of mice uniformly results in the in vivo selection of the small colony variant. We demonstrate that the spontaneous smooth small colony variant is characterized not only by a slower growth rate in vitro but also by an increased tolerance to hyperosmotic medium and, most importantly, a less effective clearance from spleens and livers of experimentally infected mice. On a molecular level, a gene with homology to a formerly described galactoside transport ATP binding protein (mglA) was differentially expressed in small versus large colonies of B. abortus S19.

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.

Attenuated signature-tagged mutagenesis mutants of Brucella melitensis identified during the acute phase of infection in mice

For this study, we screened 1,152 signature-tagged mutagenesis mutants of Brucella melitensis 16M in a mouse model of infection and found 36 of them to be attenuated in vivo. Molecular characterization of transposon insertion sites showed that for four mutants, the affected genes were only present in Rhizobiaceae. Another mutant contained a disruption in a gene homologous to mosA, which is involved in rhizopine biosynthesis in some strains of Rhizobium, suggesting that this sugar may be involved in Brucella pathogenicity. A mutant was disrupted in a gene homologous to fliF, a gene potentially coding for the MS ring, a basal component of the flagellar system. Surprisingly, a mutant was affected in the rpoA gene, coding for the essential alpha-subunit of the RNA polymerase. This disruption leaves a partially functional protein, impaired for the activation of virB transcription, as demonstrated by the absence of induction of the virB promoter in the Tn5::rpoA background. The results presented here highlight the fact that the ability of Brucella to induce pathogenesis shares similarities with the molecular mechanisms used by both Rhizobium and Agrobacterium to colonize their hosts.

Genomic analysis of secretion systems

Secretion of proteins into the extracellular environment is important to almost all bacteria, and in particular mediates interactions between pathogenic or symbiotic bacteria with their eukaryotic hosts. The accumulation of bacterial genome sequence data in the past few years has provided great insights into the distribution and function of these secretion systems. Three systems are responsible for secretion of proteins across the bacterial cytoplasmic membrane: Sec, SRP and Tat. Many novel examples of systems for transport across the Gram-negative bacterial cell envelope have been discovered through genome sequencing and surveys, including many novel type III secretion systems and autotransporters. Similarly, genomic data mining has revealed many new potential secretion substrates and identified unsuspected domains in secretion-associated proteins. Interestingly, genomic analyses have also hinted at the existence of a dedicated protein secretion system in Gram-positive bacteria, targeting members of the WXG100/ESAT-6 family of proteins, and have revealed an unexpectedly wide distribution of sortase-driven protein-targeting systems.

Smooth and rough lipopolysaccharide phenotypes of Brucella induce different intracellular trafficking and cytokine/chemokine release in human monocytes

Virulence of the intracellular pathogen Brucella for humans is mainly associated with its lipopolysaccharide (LPS) phenotype, with smooth LPS phenotypes generally being virulent and rough ones not. The reason for this association is not quite understood. We now demonstrate by flow cytometry, electron microscopy, and ELISA that human peripheral blood monocytes interact both quantitatively and qualitatively different with smooth and rough Brucella organisms in vitro. We confirm that considerably higher numbers of rough than smooth brucellae attach to and enter the monocytes in nonopsonic conditions; but only smooth brucellae replicate in the host cells. We show for the first time that rough brucellae induce higher amounts than smooth brucellae of several CXC (GRO-alpha, IL-8) and CC (MIP-1alpha, MIP-1beta, MCP-1, RANTES) chemokines, as well as pro- (IL-6, TNF-alpha) and anti-inflammatory (IL-10) cytokines released by challenged monocytes. Upon uptake, phagosomes containing rough brucellae develop selective fusion competence to form spacious communal compartments, whereas phagosomes containing smooth brucellae are nonfusiogenic. Collectively, our data suggest that rough brucellae attract and infect monocytes more effectively than smooth brucellae, but only smooth LPS phenotypes establish a specific host cell compartment permitting successful parasitism. These novel findings link the LPS phenotype of Brucella and its virulence for humans at the level of the infected host cells. Whether this is due to a direct effect of the LPS molecules or to upstream bacterial mechanisms remains to be established.

Physical map and genome sequencing survey of Mycoplasma haemofelis (Haemobartonella felis)

Mycoplasma haemofelis is an uncultivable red-cell pathogen of cats. Isolated M. haemofelis DNA was used to create a bacterial artificial chromosome library and physical map. Random sequencing of this material revealed 75 genes that had not been previously reported for M. haemofelis or any other hemotrophic mycoplasma.

Molecular host-pathogen interaction in brucellosis: current understanding and future approaches to vaccine development for mice and humans

Brucellosis caused by Brucella spp. is a major zoonotic disease. Control of brucellosis in agricultural animals is a prerequisite for the prevention of this disease in human beings. Recently, Brucella melitensis was declared by the Centers for Disease Control and Prevention to be one of three major bioterrorist agents due to the expense required for the treatment of human brucellosis patients. Also, the economic agricultural loss due to bovine brucellosis emphasizes the financial impact of brucellosis in society. Thus, vaccination might efficiently solve this disease. Currently, B. abortus RB51 and B. melitensis REV.1 are used to immunize cattle and to immunize goats and sheep, respectively, in many countries. However, these genetically undefined strains still induce abortion and persistent infection, raising questions of safety and efficiency. In fact, the REV.1 vaccine is quite virulent and apparently unstable, creating the need for improved vaccines for B. melitensis. In addition, Brucella spp. may or may not provide cross-protection against infection by heterologous Brucella species, hampering the acceleration of vaccine development. This review provides our current understanding of Brucella pathogenesis and host immunity for the development of genetically defined efficient vaccine strains. Additionally, conditions required for an effective Brucella vaccine strain as well as the future research direction needed to investigate Brucella pathogenesis and host immunity are postulated.

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.

[Brucella at the dawn of the third milenium: genomic organization and pathogenesis]

Bacteria of the genus Brucella, responsible for brucellosis, are pathogenic for animals and occasionally for humans. The cost of this widespread zoonotic infection is still very high for the community. Over the last few years, there have been advances in two main domains. First, the Brucella genome has been shown to be complex, with two circular chromosomes. Second, recent data on the virulence of Brucella suggest common mechanisms shared with plant pathogens and endosymbionts of the alpha-proteobacteria. Understanding virulence will have practical repercussions in the realms of vaccine development and, perhaps, development of new antibiotics. Two complete Brucella genome sequences are now available and will be a gold mine of information to guide future research.

Ferrochelatase is present in Brucella abortus and is critical for its intracellular survival and virulence

Brucella spp. are pathogenic bacteria that cause brucellosis, an animal disease which can also affect humans. Although understanding the pathogenesis is important for the health of animals and humans, little is known about virulence factors associated with it. In order for chronic disease to be established, Brucella spp. have developed the ability to survive inside phagocytes by evading cell defenses. It hides inside vacuoles, where it then replicates, indicating that it has an active metabolism. The purpose of this work was to obtain better insight into the intracellular metabolism of Brucella abortus. During a B. abortus genomic sequencing project, a clone coding a putative gene homologous to hemH was identified and sequenced. The amino acid sequence revealed high homology to members of the ferrochelatase family. A knockout mutant displayed auxotrophy for hemin, defective intracellular survival inside J774 and HeLa cells, and lack of virulence in BALB/c mice. This phenotype was overcome by complementing the mutant strain with a plasmid harboring wild-type hemH. These data demonstrate that B. abortus synthesizes its own heme and also has the ability to use an external source of heme; however, inside cells, there is not enough available heme to support its intracellular metabolism. It is concluded that ferrochelatase is essential for the multiplication and intracellular survival of B. abortus and thus for the establishment of chronic disease as well.