Unveiling misidentified Staphylococcus argenteus in clinical infections: Findings from a tertiary hospital in Karnataka

Purpose: Staphylococcus argenteus, a clonal member of the Staphylococcus aureus complex, is often misidentified as S. aureus using routine diagnostic methods. This study sought to differentiate clinical isolates of S. argenteus from the S. aureus complex and to evaluate their profiles of antimicrobial susceptibility. Methods: A prospective, laboratory-based study was conducted at a tertiary care centre in Karnataka, India. Sixty clinically relevant isolates belonging to the S. aureus complex were obtained from pus/tissue of skin and soft tissue infections and blood in bacteraemia. Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) was used to identify the isolates, and S. argenteus was confirmed through PCR amplification of the nonribosomal peptide synthetase (NRPS) gene. Antimicrobial susceptibility testing was undertaken following standard procedures and construed as per CLSI guidelines. Results: Three isolates (5%) were confirmed as Staphylococcus argenteus, representing the first clinically confirmed detection of this species in India. All three S. argenteus isolates were recovered from wound infections occurring in patients with underlying medical comorbidities. The isolates exhibited high susceptibility to penicillin, fluoroquinolones, vancomycin, linezolid, teicoplanin, and daptomycin. Partial NRPS gene sequencing confirmed greater similarity to Staphylococcus argenteus than to Staphylococcus schweitzeri. Conclusions: The identification of S. argenteus among clinical isolates highlights the need for advanced diagnostic tools in routine microbiology laboratories. Differentiating S. argenteus from S. aureus is essential for accurate epidemiological data, and effective MRSA surveillance.