Susceptibility of Staphylococcus aureus Strains Isolated from Blood Cultures Between 2024 and 2025: A Single-Center Study

Background: Staphylococcus aureus bloodstream infection remains a major clinical challenge because of its association with invasive disease, antimicrobial resistance, biofilm formation, and substantial mortality. Local susceptibility surveillance is essential for guiding empirical therapy and antimicrobial stewardship. This study evaluated the epidemiology, resistance patterns, turnaround time, and clinical correlates of S. aureus bacteremia in a Romanian tertiary-care hospital. Methods: We conducted a retrospective, single-center observational study including all consecutive adults with positive blood cultures for S. aureus admitted to Sibiu County Clinical Emergency Hospital between 1 January 2024 and 31 December 2025. Demographic, clinical, microbiological, antimicrobial susceptibility, and outcome data were extracted from electronic medical records. MRSA was defined phenotypically, while MDR and XDR phenotypes were classified according to standard resistance definitions. Between-year comparisons and regression analyses were performed to explore factors associated with mortality, MRSA, and MDR status. Results: During the study period, 11,578 blood culture sets were processed, of which 2472 (21.3%) were positive; S. aureus accounted for 314 isolates (12.7% of positive cultures). After one isolate per patient was retained, the final analysis included 142 patients with S. aureus bacteremia. Median age was 70 years, 55.6% were male, and 67.6% lived in urban areas. Overall mortality was 33.1% (47/142). MRSA was identified in 39.4% of cases and MDR in 49.3%, while no XDR isolates were detected. The most frequent resistances were observed for penicillin (75.9%), erythromycin (66.2%), clindamycin (46.5%), tetracycline (45.1%), and oxacillin (38.0%). Full susceptibility was preserved for vancomycin, linezolid, ceftaroline, daptomycin, and mupirocin. Turnaround time significantly improved in 2025 compared with 2024 (median 71.4 h vs. 66.3 h; p = 0.004). In adjusted analysis, acute or chronic kidney disease was independently associated with mortality, whereas MRSA and MDR status were not independent predictors of death. Conclusions: In this single-center cohort, S. aureus bacteremia was associated with high mortality and a substantial burden of MRSA and MDR phenotypes, although preserved activity of key anti-staphylococcal agents was observed. These findings support the need for continuous local resistance surveillance, rapid microbiological diagnosis, and stewardship-guided treatment strategies.