The Historical Perspective of Methicillin-Resistant Staphylococcus Aureus (Mrsa): Characterization and Quantitative Development |
Methicillin-resistantStaphylococcus aureus (MRSA) isa major cause of hospital-acquired infections that are becoming increasinglydifficult to combat because of emerging resistance to all current antibioticclasses. The evolutionary origins of MRSA are poorly understood, no rationalnomenclature exists, and there is no consensus on the number of major MRSAclones or the relatedness of clones described from different countries. Weresolve all of these issues and provide a more thorough and precise analysis ofthe evolution of MRSA clones than has previously been possible. Using multilocussequence typing and an algorithm, BURST, we analyzed an internationalcollection of 912 MRSA and methicillin susceptible S. aureus (MSSA) isolates. We identified 11 major MRSA cloneswithin five groups of related genotypes. The putative ancestral genotype ofeach group and the most parsimonious patterns of descent of isolates from eachancestor were inferred by using BURST, which, together with analysis of themethicillin resistance genes, established the likely evolutionary origins ofeach major MRSA clone, the genotype of the original MRSA clone and its MSSAprogenitor, and the extent of acquisition and horizontal movement of themethicillin resistance genes. Major MRSA clones have arisen repeatedly fromsuccessful epidemic MSSA strains, and isolates with decreased susceptibility tovancomycin, the antibiotic of last resort, are arising from some of these majorMRSA clones, highlighting a depressing progression of increasing drugresistance within a small number of ecologically successful S. aureus genotypes.