Genome-scale analysis of Staphylococcus aureus reveals host-specific diversification of the core genome.. Staphylococcus aureus

Staphylococcus aureus causes disease in humans and a wide array of animals. Of note, S. aureus mastitis of ruminants, including cows, sheep and goats, results in major economic losses worldwide. Extensive variation in genome content exists among S. aureus pathogenic clones. However, the genomic variation among S. aureus strains infecting different animal species has not been well examined. To investigate variation in the genome content of human and ruminant S. aureus we carried out whole genome PCR scanning (WGPS), comparative genomic hybridizations (CGH), and directed DNA sequence analysis of strains of human, bovine, ovine, and caprine origin. Extensive variation in genome content was discovered including host- and ruminant-specific genetic loci. Ovine and caprine strains were genetically allied whereas bovine strains were heterogenous in gene content. As expected, mobile genetic elements such as pathogenicity islands and bacteriophages contributed to the variation in genome content between strains. However, remarkably, most host-specific differences were restricted to regions of the conserved core genome, which contained allelic variation in genes encoding proteins of known and unknown function. Many of these proteins are predicted to be exported and could play a role in host-pathogen interactions. These data suggest that diversification of the core genome may be more important than acquisition of novel genes for S. aureus host-adaptation. The host-specific determinants identified by the whole-genome approaches adopted in the current study represent excellent targets for studies of the evolution and molecular basis of S. aureus host specificity. Keywords: Strain vs strain Overall design: eleven strains of Sa were compared at the DNA level in triplicate.