Prevalence of methicillin-resistant Staphylococcus aureus (MRSA) harboring mupirocin and biocide resistance genes in a large health care system

Background: We aimed to determine the prevalence of genes associated with high-level mupirocin and biocide resistance in methicillin-resistant Staphylococcus aureus (MRSA) isolates among hospitalized patients and to characterize their genomic and epidemiologic features. Methods: Study conducted on an integrated health system. Clinical cultures with MRSA from hospitalized patients collected between March 1, 2023, and January 20, 2024 underwent prospective whole-genome sequencing, including assessment for the presence of markers of resistance against mupirocin (mupA) and biocides (qac). Demographic and clinical characteristics were reviewed. Results: We analyzed 463 MRSA isolates. The overall prevalence of mupA(+), qacA(+), and qacC(+) genes was 22.0%, 2.4%, and 19.0%, respectively. Most mupA(+) isolates belonged to ST8, but ST8732 (a novel variant of ST8) had the highest prevalence of mupA(+) isolates at 95%. Patients mupA(+) were older, and none of the isolates from pediatric patients harbored this gene. Discussion: Through prospective whole-genome sequencing of MRSA isolates, we detected a prevalence of genes conferring mupirocin resistance considerably higher than previously reported, particularly among MRSA ST8 variants. Conclusions: Our findings highlight the need for monitoring resistance to agents used for the prevention of S aureus infections, as these trends have implications for infection prevention programs and public health at large.