Absence of human innate immune evasion complex in LA-MRSA ST5 strains isolated from pigs, swine facilities, and humans with swine contact

摘要

Since its first ties to swine, livestock associated methicillin-resis-tant Staphylococcus aureus (LA-MRSA) has raised public health concerns because livestock may serve as the largest reservoir of MRSA outside a hospital setting. In contrast to Europeand Asia, where the primary sequence types (ST) of swine associated LA-MRSA are ST398 and ST9 respectively, US isolates are more diverse with ST5, ST398, and ST9 being isolated.1 The presence ofST5 MRSA in swine increases concern because, unlike ST398 and ST9, ST5 MRSA is among the most prevalent lineages caus-inghuman disease.2 A primary factor contributing to the clinical impact of ST5 MRSA in the hospital (HA-MRSA) and community (CA-MRSA) is the capacity of ST5 isolates to acquire mobile genetic elements carrying virulence factors and antimicrobial resistance genes. Previous reports establishing the absence of most virulence genes from swine associated ST398 isolates3 and the lack of disease reports in humans occupationally exposed to swine carrying ST5 MRSA, suggests virulence factors contributing to human disease may also be uncommon in swine associated ST5 strains.