Corynebacterium pseudotuberculosis is a facultative intracellular pathogen and the causative agent of several infectious and
contagious chronic diseases, including caseous lymphadenitis, ulcerative lymphangitis, mastitis, and edematous skin
disease, in a broad spectrum of hosts. In addition, Corynebacterium pseudotuberculosis infections pose a rising worldwide
economic problem in ruminants. The complete genome sequences of 15 C. pseudotuberculosis strains isolated from different
hosts and countries were comparatively analyzed using a pan-genomic strategy. Phylogenomic, pan-genomic, core
genomic, and singleton analyses revealed close relationships among pathogenic corynebacteria, the clonal-like behavior of
C. pseudotuberculosis and slow increases in the sizes of pan-genomes. According to extrapolations based on the pan-genomes, core genomes and singletons, the C. pseudotuberculosis biovar ovis shows a more clonal-like behavior than the C.
pseudotuberculosis biovar equi. Most of the variable genes of the biovar ovis strains were acquired in a block through
horizontal gene transfer and are highly conserved, whereas the biovar equi strains contain great variability, both intra- and
inter-biovar, in the 16 detected pathogenicity islands (PAIs). With respect to the gene content of the PAIs, the most
interesting finding is the high similarity of the pilus genes in the biovar ovis strains compared with the great variability of
these genes in the biovar equi strains. Concluding, the polymerization of complete pilus structures in biovar ovis could be
responsible for a remarkable ability of these strains to spread throughout host tissues and penetrate cells to live
intracellularly, in contrast with the biovar equi, which rarely attacks visceral organs. Intracellularly, the biovar ovis strains are
expected to have less contact with other organisms than the biovar equi strains, thereby explaining the significant clonal-like behavior of the biovar ovis strains.
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