Lineage-specific SNPs for genotyping of Mycobacterium tuberculosis clinical isolates

Tuberculosis (TB) is a severe infectious disease worldwide. Genetic variation of the causative agent, Mycobacterium tuberculosis (MTB), determines the outcomes of infection and anti-TB treatment. Until recently, there has been no effective and convenient way for classifying clinical isolates based on the DNA sequences of the divergent lineages of MTB infecting human populations. Here, we identified single nucleotide polymorphisms (SNPs) of six representative strains from Taiwan by whole-genome sequencing and comparing the results to the sequence of the H37Rv reference strain. One hundred and ten SNPs, each unique to one of the six strains, were used to genotype 150 additional isolates by applying DNA mass spectrometry. Lineage-specific SNPs were identified that could distinguish the major lineages of the clinical isolates. A subset including 32 SNPs was found to be sufficient to type four major groups of MTB isolates in Taiwan (ancient Beijing, modern Beijing, East African-Indian, and Latin-American Mediterranean). However, there was high genetic homozygosity within the Euro-American lineage, which included spoligotype-classified Haarlem and T strains. By whole-genome sequencing of 12 representative Euro-American isolates, we identified multiple subtype-specific SNPs which allowed us to distinguish two major branches within the Euro-American lineage.