Staphylococcus aureus is a human commensal bacterium and a prominent cause of infections globally. The high incidence of S. aureus infections is compounded by the ability of the microbe to readily acquire resistance to antibiotics. In the United States, methicillin-resistant S. aureus (MRSA) is a leading cause of morbidity and mortality by a single infectious agent. Therapeutic options for severe MRSA infections are limited to a few antibiotics to which the organism is typically susceptible, including vancomycin. Acquisition of high-level vancomycin resistance by MRSA is a major concern, but to date, there have been only 12 vancomycin-resistant S. aureus (VRSA) isolates reported in the United States and all belong to a phylogenetic lineage known as clonal complex 5. To gain enhanced understanding of the genetic characteristics conducive to the acquisition of vancomycin resistance by S. aureus, V. N. Kos et al. performed whole-genome sequencing of all 12 VRSA isolates and compared the DNA sequences to the genomes of other S. aureus strains. The findings provide new information about the evolutionary history of VRSA and identify genetic features that may bear on the relationship between S. aureus clonal complex 5 strains and the acquisition of vancomycin resistance genes from enterococci.
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