Group a Streptococcus and Staphylococcus aureus: Evolution, Reemergence, and Strain Diversification

This chapter highlights key aspects of the genetic variation present in group A Streptococcus (GAS), and relates this diversity to the evolution, reemergence, and strain diversification of this biomedically important human pathogen. Acquisition of the phage encoding these genes is thought to have contributed to the evolution of virulent S. equi from its closely related but benign putative ancestor, S. zooepidemicus. Important advances in our understanding of the evolution of Staphylococcus aureus have been made in recent years. Genetic analysis of natural populations of S. aureus in the late 1980s/early1990s provided the first estimates of the degree of genetic variation among strains associated with disease and resulted in novel insights about the evolutionary relationships of strains. Other strain analysis methods have confirmed the multiclone theory of MRSA evolution, including multilocus sequence typing, ribotyping, and pulsed-field gel electrophoresis. To investigate the evolution of RD13 and the Vr, phylogenetic trees were constructed based on DNA sequence of the conserved region of RD13 and the variable set genes. Genome-scale investigation of allelic variation, population genetics, and host interactions has provided answers to longstanding controversies, such as the evolution of methicillin-resistant strains of S. aureus and the emergence of toxic shock syndrome (TSS), and provided substrates for new testable hypotheses. Genome-scale investigation of allelic variation, population genetics, and host interactions has provided answers to long-standing controversies, such as the evolution of methicillin-resistant strains of S. aureus and the emergence of TSS, and provided substrates for new testable hypotheses.