Identification of Brucella melitensis Rev.1 vaccine-strain genetic markers: Towards understanding the molecular mechanism behind virulence attenuation

Brucella melitensis Wzm/Wzt System: Changes in the Bacterial Envelope Lead to Improved Rev1Δwzm Vaccine Properties

The lipopolysaccharide (LPS) O-polysaccharide (O-PS) is the main virulence factor in Brucella. After synthesis in the cytoplasmic membrane, O-PS is exported to the periplasm by the Wzm/Wzt system, where it is assembled into a LPS. This translocation also engages a bactoprenol carrier required for further biosynthesis pathways, such as cell wall biogenesis. Targeting O-PS export by blockage holds great potential for vaccine development, but little is known about the biological implications of each Wzm/Wzt moiety. To improve this knowledge and to elucidate its potential application as a vaccine, we constructed and studied wzm/wzt single- and double-deletion mutants, using the attenuated strain Brucella melitensis Rev1 as the parental strain. This allowed us to describe the composition of Brucella peptidoglycan for the first time. We observed that these mutants lack external O-PS yet trigger changes in genetic transcription and in phenotypic properties associated with the outer membrane and cell wall. The three mutants are highly attenuated; unexpectedly, Rev1Δwzm also excels as an immunogenic and effective vaccine against B. melitensis and Brucella ovis in mice, revealing that low persistence is not at odds with efficacy. Rev1Δwzm is attenuated in BeWo trophoblasts, does not infect mouse placentas, and is safe in pregnant ewes. Overall, these attributes and the minimal serological interference induced in sheep make Rev1Δwzm a highly promising vaccine candidate.

Protein Biomarker Identification for the Discrimination of Brucella melitensis Field Isolates From the Brucella melitensis Rev.1 Vaccine Strain by MALDI-TOF MS

Brucella melitensis Rev.1 is a live attenuated vaccine strain that is widely used to control brucellosis in small ruminants. For successful surveillance and control programs, rapid identification and characterization of Brucella isolates and reliable differentiation of vaccinated and naturally infected animals are essential prerequisites. Although MALDI-TOF MS is increasingly applied in clinical microbiology laboratories for the diagnosis of brucellosis, species or even strain differentiation by this method remains a challenge. To detect biomarkers, which enable to distinguish the B. melitensis Rev.1 vaccine strain from B. melitensis field isolates, we initially searched for unique marker proteins by in silico comparison of the B. melitensis Rev.1 and 16M proteomes. We found 113 protein sequences of B. melitensis 16M that revealed a homologous sequence in the B. melitensis Rev.1 annotation and 17 of these sequences yielded potential biomarker pairs. MALDI-TOF MS spectra of 18 B. melitensis Rev.1 vaccine and 183 Israeli B. melitensis field isolates were subsequently analyzed to validate the identified marker candidates. This approach detected two genus-wide unique biomarkers with properties most similar to the ribosomal proteins L24 and S12. These two proteins clearly discriminated B. melitensis Rev.1 from the closely related B. melitensis 16M and the Israeli B. melitensis field isolates. In addition, we verified their discriminatory power using a set of B. melitensis strains from various origins and of different MLVA types. Based on our results, we propose MALDI-TOF MS profiling as a rapid, cost-effective alternative to the traditional, time-consuming approach to differentiate certain B. melitensis isolates on strain level.

Brucellosis re-emergence after a decade of quiescence in Palestine, 2015-2017: A seroprevalence and molecular characterization study

Brucellosis is an endemic disease in many developing countries and ranked by the World Health Organization among the top seven "neglected zoonoses". Although a Palestinian brucellosis control program was launched in 1998, the disease re-emerged after 2012. Interestingly, a similar re-emerging pattern was reported in the neighbouring Israeli regions. The aim of this work was to characterize the re-emerging strains and delineate their genetic relatedness. During 2015-2017, blood samples from 1324 suspected human cases were analyzed using two serological tests. Seropositive samples were cultured, and their DNAs were analyzed by different genetic markers to determine the involved Brucella species and rule out any possible involvement of the Rev.1 vaccine strain. The rpoB gene was sequenced from nine isolates to screen for rifampicin resistance mutations. Multi locus VNTR analysis (MLVA-16) was used for genotyping the isolates. The molecular analysis showed that all isolates were Brucella melitensis strains unrelated to the Rev.1 vaccine. The rpoB gene sequences showed four single nucleotide variations (SNVs) not associated with rifampicin resistance. MLVA-16 analysis clustered the isolates into 22 unique genotypes that belonged to the East Mediterranean lineage. Altogether, our findings show that the re-emergence of brucellosis was due to B. melitensis strains of local origin, the Palestinian and Israeli control programs' weaknesses could be a major factor behind the re-emergence of the disease. However, other socioeconomic and environmental factors must be investigated. Moreover, strengthening brucellosis control programs and enhancing cooperation between all stakeholders is essential to ensure long-term program outcomes to fight brucellosis.

Immunization effect of lipopolysaccharide antigen in conjugation with PLGA nanoparticles as a nanovaccine against Brucella melitensis infection

Brucella is an infectious disease with difficult treatment faced with drug resistance and recurrence of infection. Despite advances in the development of effective vaccines against brucellosis infections, there is still a need for more effective vaccine against brucellosis. In this study, we developed a nanovaccine for delivery of lipopolysaccharide Brucella melitensis antigen to the immune system using PLGA nanoparticles to prevent Brucella infection, which is associated with the stimulation of both humoral and cellular immune systems. In particular, we determined the rate of produced immunoglobulines and their functional effectiveness on the immune system by carring out opsonophagocytosis and challenge tests. According to the results, it was determined that PLGA improve the delivery of LPS antigen to the immune system to enhance the production of immunoglobulins levels and their efficiency to remove Brucella bacteria.

Genomic insights into Brucella

Brucellosis is a zoonotic disease caused by certain species of Brucella. Each species has its preferred host animal, though it can infect other animals too. For a longer period, only six classical species were recognized in the genus Brucella. No vaccine is available for human brucellosis. Therefore, human brucellosis can be controlled only by controlling brucellosis in animals. The genus is now expanding with the newly isolated atypical strains from various animals, including marine mammals. Presently, 12 species of Brucella have been recognized. The first genome of Brucella was released in 2002, and today, we have more than 1500 genomes of Brucella spp. isolated worldwide. Multiple genome sequences are available for the major zoonotic species, B. abortus, B. melitensis, and B. suis. The Brucella genome has two chromosomes with the approximate sizes of 2.1 and 1.2 Mbp. The genome of Brucella is highly conserved across all the species at the nucleotide level. One of the unanswered questions is what makes host preference in different species of Brucella. Here, I summarize the recent advancements in the Brucella genomics research.

Brucellosis in food-producing animals in Mosul, Iraq: A systematic review and meta-analysis

Brucellosis is an endemic disease in food-producing animals in Mosul, Iraq. The objectives of the study reported here were: (i) to identify and assess the evidence and knowledge gaps in published studies that have examined brucellosis in different food-producing animals in Mosul, Iraq; using systematic review approach, and (ii) to quantify the seroprevalence of brucellosis in the city using meta-analysis approach. Google Scholar was used as a search engine to track pertinent peer-reviewed research reports. The search was conducted on November 24, 2019. Keywords used were: brucella, animal, Mosul, Iraq. Peer-reviewed published studies, MSc theses, and PhD dissertations written in Arabic or English were included. Duplicate records were removed, and the screening process was conducted at three levels: titles, abstracts, and full-text articles. Identified studies that have reported the seroprevalence of brucellosis were included in a meta-analysis to calculate an overall prevalence. A total of 214 records were initially identified. Seventeen research reports were added from personal contact and qualified articles’ references list. Thirty six articles were qualified for review after removing 35 duplicate records, 155 titles, 11 abstracts, and 5 full text articles. Seventeen studies reported the prevalence of brucellosis, 11 studies assessed different serological tests for diagnosis of brucellosis, 9 studies isolated Brucella spp. from animal specimens and/or animal products, and 4 studies assessed vaccination procedures against brucellosis. The overall seroprevalence of brucellosis in food-producing animals in Mosul over a period of 40 years was 14.14%, including 14.46% for sheep, 12.99% for goats, 11.69% for cattle, and 22.64% for buffalo. The study concluded that the disease is evident in the city with increasing trends over the years, buffalo shows high seroprevalence, the degree of agreement of Rose-Bengal test as a screening test is fair compared to more accurate serological tests such as ELISA; and the disease constitutes a public health concern in the city. Additional studies are important to identify the overlooked predisposing factors, estimate the abortion rate attributable to brucellosis in food-producing animals, and evaluate efficacy of vaccination programs in reducing the prevalence of brucellosis and/or abortion rate.

Identification of Cross-Protective Potential Antigens against Pathogenic Brucella spp. through Combining Pan-Genome Analysis with Reverse Vaccinology

Brucellosis is a zoonotic infectious disease caused by bacteria of the genus Brucella. Brucella melitensis, Brucella abortus, and Brucella suis are the most pathogenic species of this genus causing the majority of human and domestic animal brucellosis. There is a need to develop a safe and potent subunit vaccine to overcome the serious drawbacks of the live attenuated Brucella vaccines. The aim of this work was to discover antigen candidates conserved among the three pathogenic species. In this study, we employed a reverse vaccinology strategy to compute the core proteome of 90 completed genomes: 55 B. melitensis, 17 B. abortus, and 18 B. suis. The core proteome was analyzed by a metasubcellular localization prediction pipeline to identify surface-associated proteins. The identified proteins were thoroughly analyzed using various in silico tools to obtain the most potential protective antigens. The number of core proteins obtained from analyzing the 90 proteomes was 1939 proteins. The surface-associated proteins were 177. The number of potential antigens was 87; those with adhesion score ≥ 0.5 were considered antigen with "high potential," while those with a score of 0.4-0.5 were considered antigens with "intermediate potential." According to a cumulative score derived from protein antigenicity, density of MHC-I and MHC-II epitopes, MHC allele coverage, and B-cell epitope density scores, a final list of 34 potential antigens was obtained. Remarkably, most of the 34 proteins are associated with bacterial adhesion, invasion, evasion, and adaptation to the hostile intracellular environment of macrophages which is adjusted to deprive Brucella of required nutrients. Our results provide a manageable list of potential protective antigens for developing a potent vaccine against brucellosis. Moreover, our elaborated analysis can provide further insights into novel Brucella virulence factors. Our next step is to test some of these antigens using an appropriate antigen delivery system.

Genomic analysis of the original Elberg Brucella melitensis Rev.1 vaccine strain reveals insights into virulence attenuation

The live attenuated Brucella melitensis Rev.1 Elberg-originated vaccine strain has been widely used to control brucellosis in small ruminants. However, despite extensive research, the molecular mechanisms underlying the attenuation of this strain are still unknown. In the current study, we conducted a comprehensive comparative analysis of the whole-genome sequence of Rev.1 against that of the virulent reference strain, B. melitensis 16M. This analysis revealed five regions of insertion and three regions of deletion within the Rev.1 genome, among which, one large region of insertion, comprising 3,951 bp, was detected in the Rev.1 genome. In addition, we found several missense mutations within important virulence-related genes, which may be used to determine the mechanism underlying virulence attenuation. Collectively, our findings provide new insights into the Brucella virulence mechanisms and, therefore, may serve as a basis for the rational design of new Brucella vaccines.