Epidemiological and comparative genomic analysis of Bacillus anthracis isolated from northern Vietnam.

To understand the epidemiological and genetic background of anthrax cases occurring in Vietnam from 2011 to 2015, we surveilled and genetically analyzed Bacillus anthracis isolated in the north of the country. Epidemiological surveillance showed that most human cutaneous anthrax cases occurred in association with animal dissection. Whole-genome sequences were obtained from six B. anthracis strains from human patients with cutaneous anthrax in the endemic area. Comparative genomic analysis showed that the genetic homogeneity among Vietnamese B. anthracis strains was very high. All Vietnamese B. anthracis strains belonged to the canSNP lineage of A.Br.011/009, which mostly consists of strains of the trans-Eurasian (TEA) group, including the most closely related strain, Carbosap. To clarify the genetic diversity of Vietnamese strains and strains belonging to A.Br.011/009 and A.Br.008/011 canSNP lineages, we applied a reference genome-based single-nucleotide polymorphism (SNP) and gene-by-gene genomic analysis (whole-genome MLST) strategy. The phylogeny from core genome SNPs revealed that the Vietnamese strains were positioned close to each other; moreover, several SNPs specific to Vietnamese B. anthracis were identified. Whole-genome MLST analysis revealed the differences in the number of SNPs between Vietnamese strains, which could enable discrimination at the strain level.