Accessory gene regulator (agr) dysfunction in Staphylococcus aureus bloodstream isolates from South Korean patients.

We describe the genetic and microbiological characteristics of methicillin-resistant Staphylococcus aureus (MRSA) bloodstream isolates with agr dysfunction from a tertiary-care hospital in Korea. Of these, ST5-SCCmec type II-agr group II MRSA isolates, which are known to be prevalent in hospital-acquired infections in Korea, were the most abundant, because of the clonal spread of a specific agr-defective lineage. This finding suggests that the loss of agr function may confer a potential advantage in a hospital setting. Clonal spread of a specific defective-agr strain was not observed among community-associated MRSA or methicillin-susceptible S. aureus clones, regardless of community or hospital acquisition of infection. agr-defective clones, including ST5 and ST239 MRSA, were enriched for heteroresistant vancomycin-intermediate S. aureus.