Advancement of a multiplex PCR for the differentiation of all currently described Brucella species

Whole-genome sequencing-based analysis of Brucella species isolated from ruminants in various regions of Türki̇ye

BACKGROUND

Brucellosis, a zoonotic disease in Türkiye, which has significant direct and indirect impacts on the healthcare system and livestock. This study, which aimed to investigate the differences among Brucella spp. isolates originating from different regions of Türkiye, for implications for public health and veterinary medicine.

METHOD

Twenty-one isolates from ruminants and two isolates from humans obtained from various regions of Türkiye were utilized in the study. The isolates were identified and biotyped using traditional microbiological procedures, and whole-genome sequencing (WGS) was performed. This was followed by single nucleotide polymorphism (SNP)--based phylogenetic analysis and WGS-based analysis of virulence and resistance genes. Additionally, phenotypic antimicrobial resistance and phage susceptibilities were determined. The obtained data were then compared for concordance, ensuring the validity and reliability of the results.

RESULTS

Our study, employing culture methods, polymerase chain reaction (PCR), and WGS analyses, identified 11 Brucella melitensis (bv 3 (n = 9), one each bv 1 and bv 2) and 12 B. abortus (bv 3 (n = 11), bv 9 (n = 1)) isolates All B. abortus isolates were of bovine origin, while the B. melitensis isolates were from sheep (n = 7), goat (n = 1), ram (n = 1), and humans (n = 2). In the whole-genome SNP-based phylogenetic tree, all B. melitensis strains were found to be of the IIb subtype of genotype II associated with the Eastern Mediterranean lineage. Ten different genotypes were identified in the SNP analysis of the isolates, with a maximum SNP difference of 278 and a minimum SNP difference of 4 among these genotypes. According to the WGS-SNP-based phylogenetic tree of B. abortus isolates, they were grouped in clade C1. In the SNP analysis, where ten different genotypes were identified, the SNP difference among these genotypes was a maximum of 316 and a minimum of 6. In the in silico MLST analysis performed with WGS data, B. melitensis isolates were identified as ST8 and ST102 genotypes, while B. abortus isolates were identified as ST2 and ST3 genotypes. The dominant genotypes were ST8 for B. melitensis and ST2 for B. abortus, respectively. Virulence gene analysis conducted based on WGS data of the 23 B. abortus and B. melitensis isolates revealed 43 virulence gene-associated regions in all strains, irrespective of species, host, or isolation year. Although classical resistance-related genes were not detected by WGS-based antimicrobial resistance gene analysis, phenotypic resistance analysis revealed resistance to azithromycin, rifampin, and trimethoprim/sulfamethoxazole in B. abortus and B. melitensis isolates.

CONCLUSION

Both B. melitensis and B. abortus were circulating species in animals and human. The dominant genotypes were ST8 for B. melitensis and ST2 for B. abortus, respectively. All B. melitensis strains were found to be of the IIb subtype of genotype II associated with the Eastern Mediterranean lineage, while B. abortus isolates, they were grouped in clade C1. Further, a comprehensive study with a sufficient number of isolates covering all regions of Türkiye would provide more accurate information about the current epidemiological situation in the country.

Combination of in silico and molecular techniques for discrimination and virulence characterization of marine Brucella ceti and Brucella pinnipedialis

Introduction

Mammals are the main hosts for Brucella sp., agents of worldwide zoonosis. Marine cetaceans and pinnipeds can be infected by Brucella ceti and B. pinnipedialis, respectively. Besides classical bacteriological typing, molecular approaches such as MLVA, MLSA, and whole-genome sequencing (WGS) can differentiate these species but are cumbersome to perform.

Methods

We compared the DNA and genome sequences of 12 strains isolated from nine marine mammals, with highly zoonotic B. melitensis, B. abortus, and B. suis, and the publicly available genomes of B. ceti and B. pinnipedialis. In silico pipelines were used to detect the antimicrobial resistance (AMR), plasmid, and virulence genes (VGs) by screening six open-source and one home-made library.

Results and discussion

Our results show that easier-to-use HRM-PCR, Bruce-ladder, and Suis-ladder can separate marine Brucella sp., and the results are fully concordant with other molecular methods, such as WGS. However, the restriction fragment length polymorphism (RFLP) method cannot discriminate between B. pinnipedialis and B. ceti B1-94-like isolates. MLVA-16 results divided the investigated strains into three clades according to their preferred host, which was confirmed in WGS. In silico analysis did not find any AMR and plasmid genes, suggesting antimicrobial susceptibility of marine Brucella, while the presence of the VGs btpA gene was variable dependent on the clade.

Conclusion

The HRM-PCR and Suis-ladder are quick, easy, and cost-effective methods to identify marine Brucella sp. Moreover, in silico genome analyses can give useful insights into the genetic virulence and pathogenicity potential of marine Brucella strains.

Evidence-practice gap analysis in the role of tick in brucellosis transmission: a scoping review

BACKGROUND

Brucellosis is a zoonotic affliction instigated by bacteria belonging to the genus Brucella and is characterized by a diverse range of pervasiveness, multiple transmission routes, and serious hazards. It is imperative to amalgamate the current knowledge and identify gaps pertaining to the role of ticks in brucellosis transmission.

METHODS

We systematically searched China National Knowledge Infrastructure (CNKI), WanFang, Google Scholar, and PubMed on the topic published until April 23, 2022. The procedure was performed in accordance with the Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines. The selected articles were categorized across three major topic areas, and the potential data was extracted to describe evidence-practice gaps by two reviewers.

RESULTS

The search identified 83 eligible studies for the final analyses. The results highlighted the potential capacity of ticks in brucellosis transmission as evidenced by the detection of Brucella in 16 different tick species. The pooled overall prevalence of Brucella in ticks was 33.87% (range: 0.00-87.80%). The review also revealed the capability of Brucella to circulate in parasitic ticks' different developmental stages, thus posing a potential threat to animal and human health. Empirical evidence from in vitro rodent infection experiments has revealed that ticks possess the capability to transmit Brucella to uninfected animals (range: 45.00-80.00%). Moreover, significant epidemiological associations have been found between the occurrence of brucellosis in animals and tick control in rangelands, which further suggests that ticks may serve as potential vectors for brucellosis transmission in ruminants. Notably, a mere three cases of human brucellosis resulting from potential tick bites were identified in search of global clinical case reports from 1963 to 2019.

CONCLUSIONS

It is imperative to improve the techniques used to identify Brucella in ticks, particularly by developing a novel, efficient, precise approach that can be applied in a field setting. Furthermore, due to the lack of adequate evidence of tick-borne brucellosis, it is essential to integrate various disciplines, including experimental animal science, epidemiology, molecular genetics, and others, to better understand the efficacy of tick-borne brucellosis. By amalgamating multiple disciplines, we can enhance our comprehension and proficiency in tackling tick-borne brucellosis.

Genotypic peculiarities of a human brucellosis case caused by Brucella suis biovar 5

Human brucellosis cases are rare in non-endemic countries, such as Germany, where infections are predominantly caused by Brucella melitensis. The German National Reference Laboratory for Bovine, Porcine, Ovine and Caprine Brucellosis received a suspected Brucella sp. isolate from a patient for identification. Bacteriological tests and PCR-based diagnostics showed the isolate to be B. suis, but did not yield cohesive results regarding the biovar. Whole genome sequencing and subsequent genotyping was employed for a detailed characterization of the isolate and elucidating the reason for failure of the diagnostic PCR to correctly identify the biovar. The isolate was found to be B. suis bv. 5, a rare biovar with limited geographical distribution primarily found in the Northern Caucasus. Due to a deletion in one of the target regions of the diagnostic PCR, the isolate could not be correctly typed. Based on in silico genotyping it could be excluded that the isolate was identical to one of the B. suis bv. 5 reference strains. Here, we report a rare case of a B. suis bv. 5 field isolate. Furthermore, by reporting this finding, we want to make practitioners aware of possible misinterpretation of PCR results, as it cannot be excluded that the detected deletion is common among the B. suis bv. 5 community, as there is currently a lack of field isolates.

Whole genome sequencing of Ethiopian Brucella abortus isolates expands the known diversity of an early branching sub-Saharan African lineage

Brucellosis remains one of the most significant zoonotic diseases globally, responsible for both considerable human morbidity and economic losses due to its impacts on livestock productivity. Despite this, there remain significant evidence gaps in many low- and middle-income countries, including those of sub-Saharan Africa. Here we report the first molecular characterisation of Brucella sp. from Ethiopia. Fifteen Brucella sp. isolates from an outbreak in cattle from a herd in central Ethiopia were identified as Brucella abortus, using bacterial culture and molecular methods. Sequencing of the Ethiopian B. abortus isolates allowed their phylogenetic comparison with 411 B. abortus strains of diverse geographical origins, using whole genome single nucleotide polymorphisms (wgSNP). The Ethiopian isolates belonged to an early-branching lineage (Lineage A) previously only represented by data from two strains, both of sub-Saharan African origin (Kenya and Mozambique). A second B. abortus lineage (Lineage B), also comprised solely of strains originating from sub-Saharan Africa, was identified. The majority of strains belonged to one of two lineages of strains originating from a much broader geographical range. Further analyses based on multi-locus sequence typing (MLST) and multi-locus variable-number tandem repeat analysis (MLVA) expanded the number of B. abortus strains available for comparison with the Ethiopian isolates and were consistent with the findings from wgSNP analysis. MLST profiles of the Ethiopian isolates expanded the sequence type (ST) diversity of the early branching lineage of B. abortus, equivalent to wgSNP Lineage A. A more diverse cluster of STs, equivalent to wgSNP Lineage B, was comprised solely of strains originating from sub-Saharan Africa. Similarly, analysis of B. abortus MLVA profiles (n = 1891) confirmed that the Ethiopian isolates formed a unique cluster, similar to only two existing strains, and distinct from the majority of other strains of sub-Saharan African origin. These findings expand the known diversity of an under-represented lineage of B. abortus and suggest a potential evolutionary origin for the species in East Africa. In addition to providing information concerning Brucella species extant within Ethiopia this work serves as the basis for further studies on the global population structure and evolutionary history of a major zoonotic pathogen.

Isolation and characterisation of Brucella melitensis by bacteriological and molecular methods from livestock in North Cyprus

In this study, the isolation, biotyping and molecular characterisation of Brucella melitensis from cattle, sheep and goats in North Cyprus are reported on. A total of 319 raw milk samples obtained from seropositive dairy livestock (190 cattle, 74 sheep and 55 goats) and tissue samples including the liver, spleen and abomasal contents obtained from 32 aborted foetal samples (5 cattle, 18 sheep and 9 goats) were analysed for the presence and characterisation of the agent. B. melitensis was isolated and identified from 90 out of 319 (28.2%) milk and 19 out of 32 (59.4%) foetal samples by conventional bacteriological methods. Identification of all 109 isolates was confirmed by using real-time PCR with genus and species-specific primers. Following the preliminary identification, 27 selected isolates representing various counties and herds were further analysed by conventional methods. Twenty (74.1%) isolates were identified as B. melitensis biovar 1 and seven (25.9%) were identified as B. melitensis biovar 3. The Bruce-ladder multiplex PCR assay revealed that all the isolates were field strains. The results of the present study confirmed the presence of B. melitensis in livestock including the cattle population in North Cyprus. Even though the majority of the samples came from seropositive cattle, Brucella abortus was not isolated in the study. The results also revealed the potential public health risk of brucellosis in livestock emphasising the need of implementing strict control and eradication strategies against the disease in animal populations in order to protect human health.

Machine Learning Algorithms for Classification of MALDI-TOF MS Spectra from Phylogenetically Closely Related Species Brucella melitensis, Brucella abortus and Brucella suis

(1) Background: MALDI-TOF mass spectrometry (MS) is the gold standard for microbial fingerprinting, however, for phylogenetically closely related species, the resolution power drops down to the genus level. In this study, we analyzed MALDI-TOF spectra from 44 strains of B. melitensis, B. suis and B. abortus to identify the optimal classification method within popular supervised and unsupervised machine learning (ML) algorithms. (2) Methods: A consensus feature selection strategy was applied to pinpoint from among the 500 MS features those that yielded the best ML model and that may play a role in species differentiation. Unsupervised k-means and hierarchical agglomerative clustering were evaluated using the silhouette coefficient, while the supervised classifiers Random Forest, Support Vector Machine, Neural Network, and Multinomial Logistic Regression were explored in a fine-tuning manner using nested k-fold cross validation (CV) with a feature reduction step between the two CV loops. (3) Results: Sixteen differentially expressed peaks were identified and used to feed ML classifiers. Unsupervised and optimized supervised models displayed excellent predictive performances with 100% accuracy. The suitability of the consensus feature selection strategy for learning system accuracy was shown. (4) Conclusion: A meaningful ML approach is here introduced, to enhance Brucella spp. classification using MALDI-TOF MS data.

Brucella spp. distribution, hosting ruminants from Greece, applying various molecular identification techniques

Background

Brucellosis still remains an endemic disease for both livestock and human in Greece, influencing the primary sector and national economy in general. Although farm animals and particularly ruminants constitute the natural hosts of the disease, transmission to humans is not uncommon, thus representing a serious occupational disease as well. Under this prism, knowledge concerning Brucella species distribution in ruminants is considered a high priority. There are various molecular methodologies for Brucella detection with however differential discriminant capacity. Hence, the aim of this survey was to achieve nationally Brucella epidemiology baseline genotyping data at species and subtype level, as well as to evaluate the pros and cons of different molecular techniques utilized for detection of Brucella species. Thirty-nine tissue samples from 30 domestic ruminants, which were found positive applying a screening PCR, were tested by four different molecular techniques i.e. sequencing of the 16S rRNA, the BP26 and the OMP31 regions, and the MLVA typing panel 1 assay of minisatellite markers.

Results

Only one haplotype was revealed from the 16S rRNA sequencing analysis, indicating that molecular identification of Brucella bacteria based on this marker might be feasible solely up to genus level. BP26 sequencing analysis and MLVA were in complete agreement detecting both B. melitensis and B. abortus. An interesting exception was observed in 11 samples, of lower quality extracted DNA, in which not all expected MLVA amplicons were produced and identification was based on the remaining ones as well as on BP26. On the contrary OMP31 failed to provide a clear band in any of the examined samples.

Conclusions

The present study reveals the constant circulation of Brucella bacteria in ruminants throughout Greece. Further, according to our results, BP26 gene represents a very good alternative to MLVA minisatellite assay, particularly in lower quality DNA samples.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03295-4.

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.

Specific Detection and Differentiation Between Brucella melitensis and Brucella abortus by a Duplex Recombinase Polymerase Amplification Assay

Brucellosis is a highly contagious zoonosis caused by a species under the genus Brucella. A duplex recombinase polymerase amplification (Duplex RPA) assay for the specific detection of Brucella melitensis and Brucella abortus was developed in this study. Primers were designed targeting hypothetical protein genes and membrane transporter genes of B. melitensis and B. abortus, respectively. The newly developed assay was validated for its analytical sensitivity and specificity. Different samples were collected from the Qinghai, Inner Mongolia, and Xinjiang provinces. After DNA extraction, the samples were analyzed by Duplex RPA, real-time PCR, and multiplex AMOS PCR to estimate the prevalence of brucellosis in sheep and yak in West China. The analytical sensitivities of Duplex RPA were 9 × 10² plasmid copies of B. melitensis and 9 × 10¹ plasmid copies of B. abortus, but by mixing the reaction tubes after 4 min of incubation, the sensitivities were 4 × 10⁰ and 5 × 10⁰ copies of B. melitensis and B. abortus, respectively. There was no cross-reactivity with Brucella suis, Chlamydia abortus, Salmonella typhimurium, Escherichia coli, and Toxoplasma gondii. The screening of field samples by Duplex RPA revealed that the prevalence of B. melitensis in sheep and yak was 75.8% and the prevalence of B. abortus was 4.8%. Multiplex AMOS PCR showed that the prevalence of B. melitensis was 19.3%, and that of B. abortus was 4.8%. It was concluded that the developed Duplex RPA is sensitive and specific to the detection of and differentiation between B. melitensis and B. abortus which will be useful in epidemiological surveillance and in the clinical settings.

Multiplex PCR Assay for the Simultaneous Detection of the Brucella Genus in Human Whole Blood and Serum

Background:

Brucellosis disease is a serious zoonosis worldwide and only 17 countries have been recognized as free of brucellosis. The World Health Organization has reported that the incidence of brucellosis is 500,000 cases in a year. Multiplex polymerase chain reaction (PCR) is an ideal method for the identification of brucellosis. The most common primers for the diagnosis of Brucella include B4/B5 and F4/R2. The advantages of multiplex PCR include targeting multiple sequences at the same time, and multiple results are produced in a single test run which saves time and the reagents simultaneously. The purpose of this investigation was to extend and optimize a multiplex PCR for the identification of genus Brucella from serum and whole blood samples.

Methods:

In this experimental and sectional study, blood samples of 25 suspected patients in the acute phase of brucellosis with serum titers higher than 1:80 were collected. Two pairs of specific primers of B4 and B5 the specific gene was amplified. PCR and Multiplex PCR were performed on blood and serum samples.

Results:

Among 25 blood samples, 15 cases (60%) and 9 cases (36%) and among 25 serum samples, 23 cases (92%) and 13 cases (52%) were positive for B4/B5 and F4/R2 in PCR, respectively. In multiplex PCR, among 25 blood samples, 5 cases (20%) showed both bands, 11 cases (44%) showed band 222bp, 4 cases (16%) showed band 905bp and 5 cases (20%) showed no bands. Among 25 serum samples, 6 cases (24%) showed both bands, 15 cases (60%) showed band 222bp, 3 cases (12%) showed band 905bp and 1 case (4%) showed no bands.

Conclusion:

The results of this study show that this multiplex PCR can be used for the diagnosis of brucellosis with high sensitivity in clinical laboratories routinely and it can serve as an alternative substitution for risky culture method and nonspecific serological methods.

Prevalence and speciation of brucellosis in febrile patients from a pastoralist community of Tanzania

Brucellosis is an endemic zoonosis in sub-Saharan Africa. Pastoralists are at high risk of infection but data on brucellosis from these communities are scarce. The study objectives were to: estimate the prevalence of human brucellosis, identify the Brucella spp. causing illness, describe non-Brucella bloodstream infections, and identify risk factors for brucellosis in febrile patients from a pastoralist community of Tanzania. Fourteen (6.1%) of 230 participants enrolled between August 2016 and October 2017 met study criteria for confirmed (febrile illness and culture positivity or ≥four-fold rise in SAT titre) or probable (febrile illness and single SAT titre ≥160) brucellosis. Brucella spp. was the most common bloodstream infection, with B. melitensis isolated from seven participants and B. abortus from one. Enterococcus spp., Escherichia coli, Salmonella enterica, Staphylococcus aureus and Streptococcus pneumoniae were also isolated. Risk factors identified for brucellosis included age and herding, with a greater probability of brucellosis in individuals with lower age and who herded cattle, sheep or goats in the previous 12 months. Disease prevention activities targeting young herders have potential to reduce the impacts of human brucellosis in Tanzania. Livestock vaccination strategies for the region should include both B. melitensis and B. abortus.

Polymorphisms in Brucella Carbonic Anhydrase II Mediate CO2 Dependence and Fitness in vivo

Some Brucella isolates are known to require an increased concentration of CO₂ for growth, especially in the case of primary cultures obtained directly from infected animals. Moreover, the different Brucella species and biovars show a characteristic pattern of CO₂ requirement, and this trait has been included among the routine typing tests used for species and biovar differentiation. By comparing the differences in gene content among different CO₂-dependent and CO₂-independent Brucella strains, we have confirmed that carbonic anhydrase (CA) II is the enzyme responsible for this phenotype in all the Brucella strains tested. Brucella species contain two CAs of the β family, CA I and CA II; genetic polymorphisms exist for both of them in different isolates, but only those putatively affecting the activity of CA II correlate with the CO₂ requirement of the corresponding isolate. Analysis of these polymorphisms does not allow the determination of CA I functionality, while the polymorphisms in CA II consist of small deletions that cause a frameshift that changes the C-terminus of the protein, probably affecting its dimerization status, essential for the activity. CO₂-independent mutants arise easily in vitro, although with a low frequency ranging from 10^–6 to 10^–10 depending on the strain. These mutants carry compensatory mutations that produce a full-length CA II. At the same time, no change was observed in the sequence coding for CA I. A competitive index assay designed to evaluate the fitness of a CO₂-dependent strain compared to its corresponding CO₂-independent strain revealed that while there is no significant difference when the bacteria are grown in culture plates, growth in vivo in a mouse model of infection provides a significant advantage to the CO₂-dependent strain. This could explain why some Brucella isolates are CO₂ dependent in primary isolation. The polymorphism described here also allows the in silico determination of the CO₂ requirement status of any Brucella strain.

Establishment of a recombinase polymerase amplification (RPA) assay for the detection of Brucella spp. Infection

Brucellosis is a worldwide re-emerging zoonosis. It has an economic impact due to abortion and loss of fertility in livestock. In this study, Real-time recombinase polymerase amplification (RT-RPA-BP26) targeting Brucella spp. bp26 gene and Lateral flow dipstick (LFD-RPA-IS711) combined with SYBR- Green recombinase polymerase amplification (RPA) targeting insertion sequence IS711 region of Brucella spp. bp26 gene, was developed to detect Brucella spp. from different sample types in domestic animals. The sensitivity and specificity of the two developed RPAs were compared with real-time PCR, PCR, and Rose Bengal Plate Test (RBPT). The analytical sensitivity and detection limit of Real-time RPA and LFD RPA were four and six copies per reaction respectively. The detection of six colony forming units (CFU) of the bacteria-bearing construct with the target sequence was within 20 min at 40 °C for Real-time RPA and 37 °C for LFD RPA. The LFD RPA could work at temperatures between 30 and 35 °C and could be completed within 10–30 min. No significant differences were observed when comparing the results from Real-time RPA and LFD RPA to Real-time PCR and PCR. Both methods showed no cross reactivity with Chlamydia abortus, Toxoplasma gondii, Salmonella typhimurium, and Escherichia coli. In conclusion, RPA is a useful and convenient field and point of care test for brucellosis.

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RPA essays have been developed for detection of Brucella spp.

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Kappa analysis showed perfect agreement with RT-PCT Nd PCR.

Molecular characterization of Brucella species from Zimbabwe

Brucella abortus and B. melitensis have been reported in several studies in animals in Zimbabwe but the extent of the disease remains poorly known. Thus, characterizing the circulating strains is a critical first step in understanding brucellosis in the country. In this study we used an array of molecular assays including AMOS-PCR, Bruce-ladder, multiple locus variable number tandem repeats analysis (MLVA) and single nucleotide polymorphisms from whole genome sequencing (WGS-SNP) to characterize Brucella isolates to the species, biovar, and individual strain level. Sixteen Brucella strains isolated in Zimbabwe at the Central Veterinary laboratory from various hosts were characterized using all or some of these assays. The strains were identified as B. ovis, B. abortus, B. canis and B. suis, with B. canis being the first report of this species in Zimbabwe. Zimbabwean strains identified as B. suis and B. abortus were further characterized with whole genome sequencing and were closely related to reference strains 1330 and 86/8/59, respectively. We demonstrate the range of different tests that can be performed from simple assays that can be run in laboratories lacking sophisticated instrumentation to whole genome analyses that currently require substantial expertise and infrastructure often not available in the developing world.

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.

Direct diagnosis of Brucella species through multiplex PCR formed by a new method

This study aimed to develop direct PCR methods, which enable the diagnosis of brucellosis agents from ruminant aborted fetus samples at species and genus levels, and determine the applicability of the newly developed methods. For this purpose, 137 lung, 137 liver, and 52 fetal stomach fluid samples belonging to 166 ruminant aborted fetuses (326 samples in total) were examined. Firstly, agent isolation and identification were performed and species-specific multiplex PCR (m-PCR) from the culture was applied to the samples. In addition, the Mayer-Scholl m-PCR method was modified and termed 'modified Mayer-Scholl', and genus specific Bcsp31 PCR was also modified with minor changes. Four different methods were applied to direct examination samples and the obtained results were compared. The conventional culture method was set as the standard method to which sensitivities and specificities of the molecular methods were calculated. According to the assessments on the basis of fetus (n = 166), sensitivity and specificity values for modified Mayer-Scholl m-PCR method were 94.11% and 98.76%, and the same indicators for the modified Bcsp31 PCR were 95.29% and 98.76%, respectively. When all organ samples were taken into account (n = 326), sensitivity and specificity values for the modified Mayer-Scholl m-PCR method were 85.38% and 98.06%, and for the modified Bcsp31 PCR, they were 83.62% and 98.06%, respectively. As a result, it was found that the diagnostic power of the tests were 'high' when results were evaluated at fetus level. On the other hand, it was found to be 'clinically useful' when evaluated at organ level. We concluded that species level identifications can be made through the modified Mayer-Scholl method, which is a direct m-PCR method, with a high diagnostic power by specifying DNAs belonging to Brucella species directly from clinical samples.

Leger J. Characterisation of North American Brucella isolates from marine mammals

Extension of known ecological niches of Brucella has included the description of two novel species from marine mammals. Brucella pinnipedialis is associated predominantly with seals, while two major Brucella ceti clades, most commonly associated with porpoises or dolphins respectively, have been identified. To date there has been limited characterisation of Brucella isolates obtained from marine mammals outside Northern European waters, including North American waters. To address this gap, and extend knowledge of the global population structure and host associations of these Brucella species, 61 isolates from marine mammals inhabiting North American waters were subject to molecular and phenotypic characterisation enabling comparison with existing European isolates. The majority of isolates represent genotypes previously described in Europe although novel genotypes were identified in both B. ceti clades. Harp seals were found to carry B. pinnipedialis genotypes previously confined to hooded seals among a diverse repertoire of sequence types (STs) associated with this species. For the first time Brucella isolates were characterised from beluga whales and found to represent a number of distinct B. pinnipedialis genotypes. In addition the known host range of ST27 was extended with the identification of this ST from California sea lion samples. Finally the performance of the frequently used diagnostic tool Bruce-ladder, in differentiating B. ceti and B. pinnipedialis, was critically assessed based on improved knowledge of the global population structure of Brucella associated with marine mammals.

Visual detection of Brucella in bovine biological samples using DNA-activated gold nanoparticles

Brucellosis is a bacterial disease, which, although affecting cattle primarily, has been associated with human infections, making its detection an important challenge. The existing gold standard diagnosis relies on the culture of bacteria which is a lengthy and costly process, taking up to 45 days. New technologies based on molecular diagnosis have been proposed, either through dip-stick, immunological assays, which have limited specificity, or using nucleic acid tests, which enable to identify the pathogen, but are impractical for use in the field, where most of the reservoir cases are located. Here we demonstrate a new test based on hybridization assays with metal nanoparticles, which, upon detection of a specific pathogen-derived DNA sequence, yield a visual colour change. We characterise the components used in the assay with a range of analytical techniques and show sensitivities down to 1000 cfu/ml for the detection of Brucella. Finally, we demonstrate that the assay works in a range of bovine samples including semen, milk and urine, opening up the potential for its use in the field, in low-resource settings.

Whole genome sequencing of Brucella melitensis isolated from 57 patients in Germany reveals high diversity in strains from Middle East

Brucellosis, a worldwide common bacterial zoonotic disease, has become quite rare in Northern and Western Europe. However, since 2014 a significant increase of imported infections caused by Brucella (B.) melitensis has been noticed in Germany. Patients predominantly originated from Middle East including Turkey and Syria. These circumstances afforded an opportunity to gain insights into the population structure of Brucella strains. Brucella-isolates from 57 patients were recovered between January 2014 and June 2016 with culture confirmed brucellosis by the National Consultant Laboratory for Brucella. Their whole genome sequences were generated using the Illumina MiSeq platform. A whole genome-based SNP typing assay was developed in order to resolve geographically attributed genetic clusters. Results were compared to MLVA typing results, the current gold-standard of Brucella typing. In addition, sequences were examined for possible genetic variation within target regions of molecular diagnostic assays. Phylogenetic analyses revealed spatial clustering and distinguished strains from different patients in either case, whereas multiple isolates from a single patient or technical replicates showed identical SNP and MLVA profiles. By including WGS data from the NCBI database, five major genotypes were identified. Notably, strains originating from Turkey showed a high diversity and grouped into seven subclusters of genotype II. MLVA analysis congruently clustered all isolates and predominantly matched the East Mediterranean genetic clade. This study confirms whole-genome based SNP-analysis as a powerful tool for accurate typing of B. melitensis. Furthermore it allows special allocation and therefore provides useful information on the geographic origin for trace-back analysis. However, the lack of reliable metadata in public databases often prevents a resolution below geographic regions or country levels and corresponding precise trace-back analysis. Once this obstacle is resolved, WGS-derived bacterial typing adds an important method to complement epidemiological surveys during outbreak investigations. This is the first report of a detailed genetic investigation of an extensive collection of B. melitensis strains isolated from human cases in Germany.

Brucella spp. of amphibians comprise genomically diverse motile strains competent for replication in macrophages and survival in mammalian hosts

Twenty-one small Gram-negative motile coccobacilli were isolated from 15 systemically diseased African bullfrogs (Pyxicephalus edulis), and were initially identified as Ochrobactrum anthropi by standard microbiological identification systems. Phylogenetic reconstructions using combined molecular analyses and comparative whole genome analysis of the most diverse of the bullfrog strains verified affiliation with the genus Brucella and placed the isolates in a cluster containing B. inopinata and the other non-classical Brucella species but also revealed significant genetic differences within the group. Four representative but molecularly and phenotypically diverse strains were used for in vitro and in vivo infection experiments. All readily multiplied in macrophage-like murine J774-cells, and their overall intramacrophagic growth rate was comparable to that of B. inopinata BO1 and slightly higher than that of B. microti CCM 4915. In the BALB/c murine model of infection these strains replicated in both spleen and liver, but were less efficient than B. suis 1330. Some strains survived in the mammalian host for up to 12 weeks. The heterogeneity of these novel strains hampers a single species description but their phenotypic and genetic features suggest that they represent an evolutionary link between a soil-associated ancestor and the mammalian host-adapted pathogenic Brucella species.

Genetic Diversity of Brucella Reference and Non-reference Phages and Its Impact on Brucella-Typing

Virulent phages have been used for many years to type Brucella isolates, but until recently knowledge about the genetic makeup of these phages remains limited. In this work the host specificity and genomic sequences of the original set (deposited in 1960) of VLA Brucella reference phages Tb, Fi, Wb, Bk2, R/C, and Iz were analyzed and compared with hitherto described brucellaphages. VLA phages turned out to be different from homonymous phages in other laboratories. The host range of the phages was defined by performing plaque assays with a wide selection of Brucella strains. Propagation of the phages on different strains did not alter host specificity. Sequencing of the phages TbV, FiV, WbV, and R/CV revealed nucleotide variations when compared to same-named phages previously described by other laboratories. The phages Bk2V and IzV were sequenced for the first time. While Bk2V exhibited the same deletions as WbV, IzV possesses the largest genome of all Brucella reference phages. The duplication of a 301 bp sequence in this phage and the large deletion in Bk2V, WbV, and R/CV may be a result of recombination caused by repetitive sequences located in this DNA region. To identify new phages as potential candidates for lysotyping, the host range and Single Nucleotide Polymorphisms (SNPs) of 22 non-reference Brucella phages were determined. The phages showed lysis patterns different from those of the reference phages and thus represent novel valuable candidates in the typing set.

The first report of Brucella suis biovar 1 isolation in human in Turkey

BACKGROUND

Brucella melitensis and B. abortus are the species generally isolated from human samples in Turkey. Several studies have also demonstrated the presence of antibodies against B. canis.

CASE REPORT AND STUDY

Brucella spp. was isolated from blood culture from a 35-year-old male with clinical signs and symptoms of acute meningitis, including fever lasting for 1 week. Multiplex PCR demonstrated B. suis, and biochemical features indicated biovar 1.

CONCLUSIONS

This report is the first emphasizing that B. suis should be considered among the causes of brucellosis in Turkey.

Development of a rapid recombinase polymerase amplification assay for detection of Brucella in blood samples

A rapid and sensitive recombinase polymerase amplification (RPA) assay, Bruce-RPA, was developed for detection of Brucella. The assay could detect as few as 3 copies of Brucella per reaction within 20 min. Bruce-RPA represents a candidate point-of-care diagnosis assay for human brucellosis.

Differential diagnosis of Brucella abortus by real-time PCR based on a single-nucleotide polymorphisms

To diagnose brucellosis effectively, many genus- and species-specific detection methods based on PCR have been developed. With conventional PCR assays, real-time PCR techniques have been developed as rapid diagnostic tools. Among them, real-time PCR using hybridization probe (hybprobe) has been recommended for bacteria with high DNA homology among species, with which it is possible to make an accurate diagnosis by means of an amplification curve and melting peak analysis. A hybprobe for B. abortus was designed from a specific single-nucleotide polymorphism (SNP) on the fbaA gene. This probe only showed specific amplification of B. abortus from approximately the 14th cycle, given a melting peak at 69°C. The sensitivity of real-time PCR was revealed to be 20 fg/µl by 10-fold DNA dilution, and the detection limit was 4 CFU in clinical samples. This real-time PCR showed greater sensitivity than that of conventional PCR and previous real-time PCR based on Taqman probe. Therefore, this new real-time PCR assay could be helpful for differentiating B. abortus infection with rapidity and accuracy.

Isolation and Identification of Brucella melitensis Biovar 3 from Vaccinated Small Ruminants: A Public Health Threat in Kosovo

In 2011, a human brucellosis case with severe clinical symptoms was reported at the University Clinic for Infectious Diseases in Prishtina, Kosovo. A trace-back investigation was conducted to find the source of human infection. A total of 49 blood samples and 15 corresponding milk samples from sheep and goats raised on the patient's farm were taken for serological and molecular analysis. Serology using RBT and CFT revealed 11 positive animals. Twelve milk samples were PCR positive. A Brucella strain isolated from a goat's milk sample was classified as Brucella melitensis biovar 3, indicating the first ever isolation and report in Kosovo. The use of the Bruce-ladder PCR provided differentiation between the field strain and the vaccine strain. Hence, the accidental transmission of the vaccine strain Rev 1 that was previously used for the vaccination of the farm animals could be excluded. The findings of this study show that brucellosis is still a public health threat in Kosovo despite control measures.

Brucella ceti infection in dolphins from the Western Mediterranean sea

BACKGROUND

Brucella ceti infections have been increasingly reported in cetaceans. Brucellosis in these animals is associated with meningoencephalitis, abortion, discospondylitis', subcutaneous abscesses, endometritis and other pathological conditions B. ceti infections have been frequently described in dolphins from both, the Atlantic and Pacific Oceans. In the Mediterranean Sea, only two reports have been made: one from the Italian Tyrrhenian Sea and the other from the Adriatic Sea.

RESULTS

We describe the clinical and pathological features of three cases of B. ceti infections in three dolphins stranded in the Mediterranean Catalonian coast. One striped dolphin had neurobrucellosis, showing lethargy, incoordination and lateral swimming due to meningoencephalitis, A B. ceti infected bottlenose dolphin had discospondylitis, and another striped dolphin did not show clinical signs or lesions related to Brucella infection. A detailed characterization of the three B. ceti isolates was performed by bacteriological, molecular, protein and fatty acid analyses.

CONCLUSIONS

All the B. ceti strains originating from Mediterranean dolphins cluster together in a distinct phylogenetic clade, close to that formed by B. ceti isolates from dolphins inhabiting the Atlantic Ocean. Our study confirms the severity of pathological signs in stranded dolphins and the relevance of B. ceti as a pathogen in the Mediterranean Sea.

Polymerase chain reaction-based assays for the diagnosis of human brucellosis

Polymerase chain reaction (PCR) is an in vitro technique for the nucleic acid amplification, which is commonly used to diagnose infectious diseases. The use of PCR for pathogens detection, genotyping and quantification has some advantages, such as high sensitivity, high specificity, reproducibility and technical ease. Brucellosis is a common zoonosis caused by Brucella spp., which still remains as a major health problem in many developing countries around the world. The direct culture and immunohistochemistry can be used for detecting infection with Brucella spp. However, PCR has the potential to address limitations of these methods. PCR are now one of the most useful assays for the diagnosis in human brucellosis. The aim of this review was to summarize the main PCR techniques and their applications for diagnosis and follow-up of patients with brucellosis. Moreover, advantages or limitation of the different PCR methods as well as the evaluation of PCR results for treatment and follow-up of human brucellosis were also discussed.

A duplex PCR for rapid and simultaneous detection of Brucella spp. in human blood samples

OBJECTIVE

To design a duplex PCR for rapid and simultaneous detection of Brucella species. in human blood samples.

METHODS

Fifty-two peripheral bloods samples were collected from suspicious patients with brucellosis. Following DNA extraction, PCR assay were performed, using three primers that could simultaneously identify and differentiate three major species of pathogenic Brucella in humans and animals.

RESULTS

Of the 52 peripheral bloods samples tested, 25 sample (48%) showed positive reactions in PCR. Twelve samples were positive for Brucella abortus 39 (B. abortus 39) (23%), 13 for Brucella melitensis 39 (B. melitensis 39) (25%) and 0 for Brucella ovis 39 (B. ovis 39) (0%).

CONCLUSIONS

This work demonstrates that in case where specific primers were utilized, duplex PCR has proved to be a simple, fast, and relatively inexpensive method for simultaneous detection of important species of Brucella in clinical samples.

Implications of laboratory diagnosis on brucellosis therapy

Brucellosis is a worldwide zoonosis with a huge economic impact on animal husbandry and public health. The diagnosis of human brucellosis can be protracted because the disease primarily presents as fever of unknown origin with unspecific clinical signs and symptoms. The isolation rate of the fastidious etiologic agent from blood cultures is low, and therefore laboratory diagnosis is mainly based on serologic and molecular testing. However, seronegative brucellosis patients have been described, and antibody titers of diagnostic significance are difficult to define. Whether the molecular detection of Brucella DNA in clinical samples should be followed by long-term antibiotic treatment or not is also a matter of debate. The aim of this article is to review and discuss the implications of laboratory test results in the diagnosis of human brucellosis on disease therapy.

Intraspecies biodiversity of the genetically homologous species Brucella microti

Brucellosis is one of the major bacterial zoonoses worldwide. In the past decade, an increasing number of atypical Brucella strains and species have been described. Brucella microti in particular has attracted attention, because this species not only infects mammalian hosts but also persists in soil. An environmental reservoir may pose a new public health risk, leading to the reemergence of brucellosis. In a polyphasic approach, comprising conventional microbiological techniques and extensive biochemical and molecular techniques, all currently available Brucella microti strains were characterized. While differing in their natural habitats and host preferences, B. microti isolates were found to possess identical 16S rRNA, recA, omp2a, and omp2b gene sequences and identical multilocus sequence analysis (MLSA) profiles at 21 different genomic loci. Only highly variable microsatellite markers of multiple-locus variable-number tandem repeat (VNTR) analysis comprising 16 loci (MLVA-16) showed intraspecies discriminatory power. In contrast, biotyping demonstrated striking differences within the genetically homologous species. The majority of the mammalian isolates agglutinated only with monospecific anti-M serum, whereas soil isolates agglutinated with anti-A, anti-M, and anti-R sera. Bacteria isolated from animal sources were lysed by phages F1, F25, Tb, BK2, Iz, and Wb, whereas soil isolates usually were not. Rough strains of environmental origin were lysed only by phage R/C. B. microti exhibited high metabolic activities similar to those of closely related soil organisms, such as Ochrobactrum spp. Each strain was tested with 93 different substrates and showed an individual metabolic profile. In summary, the adaptation of Brucella microti to a specific habitat or host seems to be a matter of gene regulation rather than a matter of gene configuration.

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.

New Bruce-ladder multiplex PCR assay for the biovar typing of Brucella suis and the discrimination of Brucella suis and Brucella canis

Rapid and specific identification of Brucella suis at the biovar level is necessary because some of the biovars that infect animals are pathogenic for humans. None of the molecular typing methods described so far are able to discriminate B. suis biovars in a single test and differentiation of B. suis from Brucella canis by molecular approaches can be difficult. This article describes a new multiplex PCR assay, Suis-ladder, for fast and accurate identification of B. suis at the biovar level and the differentiation of B. suis, B. canis and Brucella microti. An advancement of the original Bruce-ladder PCR protocol which allows the correct discrimination of all known Brucella species is also described.

Advanced multiplex PCR assay for differentiation of Brucella species

Two new primer sets of a 766- and a 344-bp fragment were introduced into the conventional Bruce-ladder PCR assay. This novel multiplex PCR assay rapidly and concisely discriminates Brucella canis and Brucella microti from Brucella suis strains and also may differentiate all of the 10 Brucella species.

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.

Review of detection of Brucella spp. by polymerase chain reaction

Here we present a review of most of the currently used polymerase chain reaction (PCR)-based methods for identification of Brucella bacteria in biological samples. We focused in particular on methods using single-pair primers, multiplex primers, real-time PCRs, PCRs for marine Brucella, and PCRs for molecular biotyping. These methods are becoming very important tools for the identification of Brucella, at the species level and recently also at the biovar level. These techniques require minimum biological containment and can provide results in a very short time. In addition, genetic fingerprinting of isolates aid in epidemiological studies of the disease and its control. PCR-based methods are more useful and practical than conventional methods used to identify Brucella spp., and new methods for Brucella spp. identification and typing are still being developed. However, the sensitivity, specificity, and issues of quality control and quality assurance using these methods must be fully validated on clinical samples before PCR can be used in routine laboratory testing for brucellosis.

Loop-mediated isothermal amplification assay targeting the omp25 gene for rapid detection of Brucella spp

A novel loop-mediated isothermal amplification (LAMP) assay was established to detect Brucella species DNA in milk and blood samples of animals and humans. This LAMP assay based on the sequence of highly repetitive omp25 gene was able to detect 9fg/μl Brucella spp. DNA with high sensitivity, which was 10 times higher than the nested PCR. The LAMP was evaluated for its specificity using 19 strains of six Brucella species and 28 related non-Brucella micro-organism strains as controls. The target 19 Brucella strains were all amplified, and no cross-reaction was found with all the non-Brucella micro-organism strains. Both nested PCR and LAMP assays were then used to detect Brucella spp. DNA in 78 milk samples and 113 blood samples from animals and 11 blood samples from humans, and the established LAMP assay yielded 99.0% concordance rate with the nested PCR. The LAMP assay should be a potential tool with high convenience, rapidity, sensitivity and specificity for the diagnosis of Brucellosis.

Ribosomal RNA sequence analysis of Brucella infection misidentified as Ochrobactrum anthropi infection

A Brucella isolate was identified from purulent material collected during a hip surgery. Two previous blood cultures from the same patient yielded Ochrobactrum anthropi. After rRNA sequencing, all the isolates were identified as Brucella species and subsequently serotyped as Brucella suis. Misidentification of Brucella species remains a problem with bacterial identification systems.

Ovine and Caprine Brucellosis (Brucella melitensis) in Aborted Animals in Jordanian Sheep and Goat Flocks

Two hundred and fifty five biological samples were collected from 188 animals (81 sheep and 107 goats) during the lambing season from September 2009 to April 2010 from the Mafraq region of Jordan. Sampled animals belonged to 93 sheep and goat flocks that had abortion cases in the region. One hundred and seven (41.9%) biological samples were positive for the omp2 primers that were able to identify all Brucella species in the collected samples which were obtained from 86 aborted animals (86/188 = 45.7%). Using the B. melitensis insertion sequence 711 (IS711) primers on the 107 omp2 positive samples, only 61 confirmed to be positive for B. melitensis. These positive samples were obtained from 28 sheep and 33 goats. The prevalence rate of B. melitensis was 27.1% (51/188) among aborted animals. For differentiation between vaccine strain and field strain infection, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method using PstI endonuclease enzyme was used. Vaccination with Rev-1 in the last year (OR = 2.92, CI: 1.1–7.7) and grazing at common pasture (OR = 2.78, CI: 1.05–7.36) were statistically significant (P ≤ .05) risk factors positively associated with the occurrence of brucellosis in sheep and goat flocks.