Five-year cumulative antimicrobial resistance profiles of respiratory tract isolates in a tertiary care center (2021–2025)

Aims: The success of empirical treatment for Streptococcus pneumoniae (S. pneumoniae), Haemophilus influenzae (H. influenzae),and Moraxella catarrhalis (M. catarrhalis) depends on current antimicrobial resistance (AMR) profiles. This study aimed to determine the five-year cumulative AMR profiles and trends in a tertiary care center.Methods: Strains isolated from lower respiratory tract samples between 2021 and 2025 were retrospectively analyzed. Identification was performed via MALDI-TOF MS; susceptibilities were determined by the Phoenix M50 system and disk diffusion according to EUCAST criteria. Cumulative data were analyzed following KLİMUD guidelines, including only the first isolate from each patient.Results: A total of 1870 isolates (1075 H. influenzae, 501 S. pneumoniae, 294 M. catarrhalis) were evaluated. High resistance rates were found in S. pneumoniae for erythromycin (47.9%), penicillin (45.2%), and tetracycline (45.2%), while no resistance to vancomycin or meropenem was detected. In H. influenzae, resistance rates were 37.0% for ampicillin, 37.9% for trimethoprim sulfamethoxazole, and 12.4% for amoxicillin-clavulanate. M. catarrhalis exhibited low resistance rate to amoxicillin-clavulanate (2.5%) and macrolides (0.7%). Conclusion: The study demonstrates that resistance to conventional oral antibiotics has reached critical levels in S. pneumoniae and H. influenzae, while Moraxella catarrhalis has maintained a relatively susceptible profile. Tailoring empirical treatment protocols based on local cumulative antibiogram data is essential.