The emergence and importation of diverse genotypes of methicillin-resistant Staphylococcus aureus (MRSA) harboring the Panton-Valentine leukocidin gene (pvl) reveal that pvl is a poor marker for community-acquired MRSA strains in Ireland

Abstract

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) carrying pvl is an emerging problem worldwide. CA-MRSA tends to harbor staphylococcal cassette chromosome mec type IV (SCCmec IV), to be non-multiantibiotic resistant, and to have different genotypes from the local hospital-acquired MRSA (HA-MRSA). However, in Ireland, 80% of HA-MRSA isolates have the non-multiantibiotic-resistant genotype ST22-MRSA-IV. This study investigated MRSA isolates from Ireland (CA-MRSA, health care-associated MRSA, and HA-MRSA) for the carriage of pvl and determined the genotypic characteristics of all pvl-positive isolates identified. All 1,389 MRSA isolates were investigated by antibiogram-resistogram typing and SmaI DNA macrorestriction analysis. pvl-positive isolates were further characterized by multilocus sequence typing and SCCmec, agr, and toxin gene typing. Twenty-five (1.8%) MRSA isolates belonging to six genotypes (ST30, ST8, ST22, ST80, ST5, and ST154) harbored pvl. Nineteen of these (76%) were CA-MRSA isolates, but a prospective study of MRSA isolates from 401 patients showed that only 6.7% (2/30) of patients with CA-MRSA yielded pvl-positive isolates. Thus, pvl cannot be used as a sole marker for CA-MRSA. Fifty-two percent of pvl-positive MRSA isolates were recovered from patients with skin and soft tissue infections; thirty-six percent were from patients of non-Irish ethnic origin, reflecting the increasing heterogeneity of the Irish population due to immigration. All 25 pvl-positive isolates carried SCCmec IV; 14 (56%) harbored SCCmec IV.1 or IV.3, and the remaining 11 isolates could not be subtyped. This study demonstrates that pvl is not a reliable marker for CA-MRSA in Ireland and reveals the emergence and importation of diverse genotypes of pvl-positive MRSA in Ireland.