Antimicrobial Resistance Trends in Streptococcus pneumoniae and Haemophilus influenzae: A 13-Year SENTRY Surveillance Study from Turkey (2010 – 2023)

Background: Local surveillance of antimicrobial resistance is essential to guide empirical treatment strategies for respiratory tract infections. Long-term local data are particularly important in the context of rising global resistance and regional variations in antimicrobial susceptibility patterns, enabling clinicians to make informed empirical therapy decisions. Objectives: This study aimed to determine and compare antimicrobial resistance rates in Streptococcus pneumoniae (n = 335) and Haemophilus influenzae (n = 185) isolates obtained from community-acquired respiratory tract infections at Hacettepe University Hospital between 2010 and 2023. Methods: Streptococcus pneumoniae and H. influenzae isolates (one isolate per patient) recovered from sputum, tracheal aspirate, or bronchoalveolar lavage samples of patients with community-acquired pneumonia were included in the SENTRY surveillance program. Antimicrobial susceptibilities were determined by the microdilution method according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines (2025) using cation-adjusted Mueller–Hinton broth supplemented with lysed horse blood. Results: Penicillin non-susceptibility (I+R) was 67.2% in S. pneumoniae isolates (42.7% intermediate, 24.5% resistant), while ampicillin resistance in H. influenzae was 13.0%. All S. pneumoniae isolates remained fully susceptible to meropenem, linezolid, and vancomycin. Ceftaroline resistance rates were 1.5% in S. pneumoniae and 3.2% in H. influenzae. No resistance to ceftriaxone was detected among H. influenzae isolates. Conclusions: High rates of penicillin and macrolide non-susceptibility in S. pneumoniae limit the empirical use of these agents in our setting. In contrast, ceftriaxone and respiratory fluoroquinolones remain highly effective options for the empirical treatment of community-acquired respiratory tract infections. These findings underscore the importance of continuous local surveillance to support rational antimicrobial therapy.