Abstract
BACKGROUND: Staphylococcus argenteus is a coagulase-positive species within the Staphylococcus aureus complex that may carry the mecA gene, conferring methicillin resistance. Despite its clinical relevance, methicillin-resistant S. argenteus (MRSArg) remains underreported and poorly characterized in many regions. AIM: This study presents the first nationwide analysis of MRSArg in Norway, detected among MRSA 18,152 isolates submitted to the Norwegian MRSA Reference Laboratory between 2008 and 2019. METHODS: Clinical and epidemiological data were retrieved from national surveillance systems and laboratory records, enabling classification into healthcare- and community-associated categories. A representative panel of MRSArg genotypes (n = 25) was inoculated onto four MRSA-selective chromogenic agars for qualitative assessment of growth characteristics and colony pigmentation, and into two enrichment broths for quantitative evaluation of stationary-phase cell density. Identification was performed using MALDI-ToF MS and GeneXpert assays. Whole genome sequencing of 160 isolates enabled phylogenetic analysis, resistance and virulence profiling, and cgMLST. A species-specific multiplex PCR targeting yhfT, mecA, and lukE, along with adapted spa-typing primers, was developed for accurate molecular identification and typing. RESULTS: A total of 160 mecA-positive MRSArg strains (0.9%) were identified, corresponding to 142 unique patients. Most cases were community-associated and linked to international acquisition, particularly from Southeast Asia. However, 36% were healthcare-associated, including a notable proportion among healthcare workers. The dominant genotype was spa-type t6675/ST2250 (50%), with increasing diversity observed after 2014. A species-specific multiplex-PCR and sanger sequencing primers for detection and genotyping of MRSArg were developed and validated. CONCLUSION: MRSArg is an emerging pathogen in Norway with both community and healthcare relevance. Improved molecular diagnostics are essential for accurate detection and surveillance.