Whole-Genome Sequencing of Brucella melitensis Isolates from Kuwait for the Identification of Biovars, Variants, and Relationship within a Biovar.

Abstract

Objective: The identification of Brucella genotypes is essential for epidemiological studies. The whole-genome sequencing is emerging as a novel tool for genetic characterization of infectious microbes. The aim of this study was to genotype Brucella melitensis isolates from Kuwait using whole-genome sequencing and variant analysis of the sequence data.

Methods: DNA was purified from 15 heat-inactivated B. melitensis isolates and used to prepare sequencing libraries employing Nextera XT DNA Sample Preparation Kit (Illumina San Diego, CA, USA) and sequenced on a MiSeq (Illumina). The sequence files were aligned to three biovars of B. melitensis, i.e., biovar 1 str. 16M, biovar 2 str. 63/9, and biovar 3 str. Ether. The alignment and variant calling were performed using "bwa-mem" and SAMtools/VCFtools, respectively.

Results: The genome size of all the isolates was around 3.3 mega base pairs and resembled B. melitensis biovar 2. Single-nucleotide polymorphisms (SNPs), insertions, and deletions (indels) were spread all over the genome; but 138 SNPs were common among the 14 isolates, supporting the same ancestral origin. A neighbor-joining tree analysis identified isolate 2 as an outlier. In addition, SNPs (2-478) specific to each isolate were also identified, which divided the B. melitensis biovar 2 into two major groups/genotypes. A further analysis showed that the Kuwaiti isolates of the present study shared phylogeny mainly with strains from the Middle Eastern countries.

Conclusions: Among the 15 studied isolates from Kuwait, biovar 2 is the most prevalent biovar of B. melitensis. Furthermore, isolate-specific genetic variations were identified, which may be useful in epidemiological investigations.