Molecular Characteristics of Nosocomial and Native American Community-Associated Methicillin-Resistant Staphylococcus aureus Clones from Rural Wisconsin

Abstract

ABSTRACT In central and northern Wisconsin methicillin-resistant Staphylococcus aureus (MRSA) was first detected in 1989. Over the next 10-year period, 581 MRSA isolates were collected, 17.2% of which came from patients who were treated at five Native American clinics. These isolates were typed by SmaI-macrorestricted pulsed-field gel electrophoresis (PFGE). The PFGE patterns clustered the isolates into six major clonal groups (MCGs), i.e., MCGs 1 to 6, and 19 minor clonal groups ( m CGs). The 25 clonal groups were represented by 109 unique PFGE types. Sixty-five percent of the MCG-2 isolates were recovered from patients who were treated at Native American clinics. Ninety-four percent of the MCG-2 isolates harbored the staphylococcal cassette chromosome mec (SCC mec ) IVa. These isolates also had PFGE profiles that were clonally related to the midwestern community-associated MRSA (CA-MRSA) strain, MW2. The representative isolates from MCG-2 had the multilocus sequence type allelic profile 1-1-1-1-1-1-1 and contained pvl genes. They were also susceptible to various antibiotics, a finding consistent with the CA-MRSA phenotype. SCC mec IV was also present in other m CGs. Unlike MCG-2, isolates from the remaining five MCGs harbored SCC mec II and were resistant to multiple antibiotics, suggesting their nosocomial origin. The 19 m CGs were represented by diverse SCC mec types and three putative new variants referred to as SCC mec Ib, IIa, and IIb.