Comparative genomic analysis of Chinese human leptospirosis vaccine strain and circulating isolate.

Leptospira interrogans serogroup Canicola is one of the most important pathogens causing leptospirosis and is used as a vaccine strain of the current Chinese human leptospirosis vaccine. To characterize leptospiral pathogens, L. interrogans serogroup Canicola vaccine strain 611 and circulating isolate LJ178 from different hosts at different periods were sequenced using a combined strategy of Illumina X10 and PacBio technologies, and a comprehensive comparative analysis with other published Leptospira strains was conducted in this study. High levels of genomic similarities were observed between vaccine strain 611 and circulating isolate LJ178; both had two circular chromosomes and two circular extrachromosomal replicons. Compared with the strain 611 genome, 132 single nucleotide polymorphisms and 92 indels were found in strain LJ178. The larger lipopolysaccharide biosynthesis locus of serogroup Canicola was identified in both genomes. The phylogenetic analysis based on whole-genome sequences revealed that serogroup Canicola was not restricted to a specific host or geographic location, suggesting adaptive evolution associated with the ecologic diversity. In summary, our findings provide insights into a better molecular understanding of the component strains of human leptospirosis vaccine in China. Furthermore, these data detail the genetic composition and evolutionary relatedness of Leptospira strains that pose a health risk to humans.