Genome Sequences of Human and Livestock Isolates of Brucella melitensis and Brucella abortus from the Country of Georgia

ABSTRACT Brucellosis, which is among the most widespread global zoonotic diseases, is endemic in the nation of Georgia and causes substantial human morbidity and economic loss. Here, we report whole-genome sequences of three Brucella melitensis and seven Brucella abortus isolates from cattle, sheep, and humans that represent genetic groups discovered in Georgia.

B rucellosis is one of the most globally common zoonotic diseases, with more than 500,000 human cases reported worldwide annually (1). Brucellosis epidemiology changes under various sanitary, socioeconomic, and political conditions. The genus Brucella comprises facultative intracellular bacterial pathogens that can infect a wide range of mammals, including humans, livestock, rodents, and marine mammals (2,3). Five Brucella species are known to be pathogenic for humans: B. melitensis, B. abortus, B. suis, B. canis, and B. maris (4). Among these, B. abortus and B. melitensis are classified as category B biological threat agents (5) (https://emergency.cdc.gov/agent/agentlist.asp).
Molecular typing assays are routinely used to genetically characterize Brucella isolates and determine clonal associations, and thus provide a means to trace-back to sources of infection, and can also be used to discriminate naturally occurring outbreaks from a bioterrorism event. The genetic typing tool multiple-locus variable-number tandem-repeat analysis (MLVA) can provide high-resolution genetic subtyping information for accurate epidemiological investigations (6). In this study, we used a 15marker MLVA system (7) to subtype Brucella strains isolated in Georgia between 2010 and 2013. Based on this analysis, 10 isolates, including three B. melitensis and seven B. abortus strains, were selected to represent major genetic clusters for whole-genome pyrosequencing (Table 1). Purified Brucella genomic DNA samples were sheared to around 1-kb-long fragments using the Covaris S2 system (Covaris, Woburn, MA). The shotgun library of DNA fragments for each sample was prepared and sequenced using Roche GS FLX sequencing system and reagents (Roche 454 Life Sciences, Branford, CT). Sequence read data were successfully assembled into de novo assembly contigs using Roche GS Assembler software (Newbler), with most sequence reads assembled and high sequence alignment depths achieved ( Table 1). The size of each draft genome, as estimated based on the length and copy number of every contig, is close to the expected length of 3.3 Mb. The sequences share high nucleotide identity (Ͼ99%) with respective known Brucella genome sequences, including GenBank reference genomes (RefSeq) B. abortus S19 (accession numbers NC_010740 and NC_010742) and B. melitensis M28 (accession numbers NC_017244 and NC_017245). The draft genomes were annotated by utilizing the NCBI Prokaryotic Genome Annotation Pipeline (PGAP, revision 33 [http://www.ncbi.nlm.nih.gov/genomes/static/Pipeline.html]) ( Table 1).
Brucellosis remains a major agricultural and public health problem in the nation of Georgia (8,9). Acquisition of genome sequences for representative genetic variants of the two most important pathogenic Brucella species will enable genome-wide phylogenetic and polymorphism analyses to enhance brucellosis surveillance in Georgia. To our knowledge, these are the first published whole-genome sequences of Brucella isolates from Georgia or the broader South Caucasus region. Work under way includes comparative analyses of these and other Brucella genomes to identify unique single nucleotide polymorphisms (SNPs) and genome structural variations for understanding of Brucella pathogenicity and the application of this genomic information to brucellosis epidemiology and disease control.
Accession number(s). The whole-genome sequences for B. abortus and B. melitensis were deposited in GenBank under BioProject numbers PRJNA338234 and PRJNA339926, respectively, with accession numbers listed in Table 1.

ACKNOWLEDGMENTS
The views expressed herein are those of the authors and do not reflect the official policy or positions of the Walter Reed Army Institute of Research, Department of the Army, Department of Defense, or the U.S. Government.
We declare no conflicts of interest. This work was supported by the Defense Threat Reduction Agency (CBCALL12-DIAGB1-2-0194) and the Armed Forces Health Surveillance Branch Global Emerging Infections Surveillance and Response System. J.H. and M.P.N. are employees of the U.S. Government. This work was done as part of their official duties. Title 17 USC §105 provides that "Copyright protection under this title is not available for any work of the United States Government." Title 17 USC §101 defines U.S. Government work as a work prepared by employee of the U.S. Government as part of that person's official duties.