Ten-year surveillance of antimicrobial susceptibility patterns of Staphylococcus aureus in a tertiary care hospital: a retrospective laboratory-based study

Staphylococcus aureus ( S. aureus ) is a major cause of community- and hospital-acquired infections worldwide. Rising methicillin-resistant S. aureus (MRSA) prevalence poses significant therapeutic challenges, making continuous local surveillance essential for antimicrobial stewardship. To determine 10-year trends in S. aureus isolation, evaluate antimicrobial susceptibility profiles, and analyze MRSA/MSSA distribution across clinical settings. This retrospective study analyzed non-duplicate clinical S. aureus isolates (2015–2024). Isolates were identified via MALDI-TOF mass spectrometry and tested for antimicrobial susceptibility using Kirby–Bauer disk diffusion per CLSI guidelines. exploratory molecular sub-cohort ( n = 50) collected between 2021 and 2023 using stratified random sampling. Temporal patterns were analyzed utilizing binary logistic regression. Multivariable logistic regression was applied to adjust for potential confounding by clinical setting and specimen type. Out of 42,343 clinical specimens, 314 S. aureus isolates were recovered, showing a declining recovery rate over time (OR = 0.91, ). Phenotypic MRSA comprised 69.4% (218/314) of isolates. MRSA rates were significantly higher in inpatient wards (76.4%) and ICUs (75.6%) than in the OPD (56.9%; ). Comparing 5-year blocks (2015–2019 vs. 2020–2024), the odds of MRSA increased significantly (OR = 1.66, ). Overall weighted resistance among MRSA isolates across testing years was highest for azithromycin (95.4%), erythromycin (92.5%), levofloxacin (73.4%), gentamycin (71.6%), co-trimoxazole (62.8%), and clindamycin (62.8%), with linezolid showing lower overall resistance (15.1%). Long-term analysis revealed a significant linear increase in levofloxacin resistance (OR = 1.41, ) and a rising trend for linezolid (OR = 1.14, ). Genotypic analysis revealed that 93.1% (27/29) of MRSA strains carried mecA , while 71.4% (15/21) of MSSA strains exhibited cefoxitin-susceptible, mecA -positive ( MSSA) profiles. The detection of mecA -positive cefoxitin-susceptible strains in the molecular sub-cohort indicates a masked genomic resistance reservoir requiring further investigation with functional expression assays.