Antimicrobial susceptibility profile of clinical isolates of Staphylococcus aureus and Staphylococcus capitis

Abstract

Introduction: antimicrobial resistance is one of the primary health challenges of the 21st century, associated with the indiscriminate use of antibiotics and the emergence of resistant strains. Staphylococcus, a genus widely present in the human microbiota, includes clinically relevant species, such as coagulase-positive and coagulase-negative staphylococci, which exhibit to multiple classes of antimicrobials. Objective: to characterise the antimicrobial susceptibility profile of clinical isolates of Staphylococcus aureus and Staphylococcus capitis clinical isolates. Methodology: the isolates were obtained from the Microbiological Library of the Institute of Health Sciences of the Federal University of Bahia. The species were identified by MALDI-TOF MS mass spectrometry and morpho-staining characterized by Gram staining. The susceptibility profile was determined using the second diffusion technique, which employed new antimicrobials to interpret the BrCAST-EUCAST 2025 criteria. Results: the S. aureus isolate showed resistance to almost all antimicrobials tested (8/9), including β-lactams, aminoglycosides, and macrolides, characterising the MRSA phenotype. The S. capitis isolate showed a broadly susceptible profile, with restricted resistance to clindamycin. Susceptibility to vancomycin was inconclusive. Conclusion: the results highlight the importance of phenotypic characterisation of antimicrobial resistance in clinical isolates of Staphylococcus, and demonstrate its contribution to strengthening microbiological surveillance in different settings.