Comparative genome analysis of virulent strains of Bacillus anthracis causing anthrax outbreaks in animals

Anthrax, caused by the bacterial pathogen Bacillus anthracis, is a lethal disease affecting both livestock and humans. This study focused on the comparative whole-genome analysis of two Indian virulent Bacillus anthracis strains recovered from anthrax cases in cattle (NIVEDIAX3) and sheep (NIVEDIAX61), and their comparison with available genomes (n = 55) in the NCBI database. Phylogenetic analysis based on average nucleotide identity clustered the 57 strains into 3 groups, with both NIVEDIAX strains grouped under Cluster II, alongside the Ames Ancestor strain. Multilocus sequence typing (MLST) assigned the strains to Bacillus cereus sequence type ST1, Bacillus anthracis core genome MLST ST284, and Bacillus anthracis plasmid ST12 based on typing scheme. A total of 5217 orthologous clusters and 468 single-copy gene clusters shared between the NIVEDIAX strains and the Ames Ancestor strain were identified. Canonical single nucleotide polymorphism (canSNP) analysis classified both strains as A.Br.003 (A.Br.Aust94 sub-lineage). Further, analysis of the 57 Bacillus anthracis genomes revealed that A.Br.003 was the most prevalent canSNP among animal isolates. In India, multiple Bacillus anthracis sub-lineages have been reported. In conclusion, the circulation of diverse Bacillus anthracis sub-lineages in livestock across Southern and Eastern states of India, was noted.