Streptococcus pneumoniae Invasive and Bronchoalveolar Lavage Isolates in Adult Patients in Türkiye (2019-2025): Serotype Distribution, Antibiotic Resistance, and Serotype Coverage of Pneumococcal Vaccine.

OBJECTIVE: To determine the serotype distribution, antibiotic susceptibility, and vaccine serotype coverage of Streptococcus pneumoniae isolates from adult patients in Türkiye. METHODS: This laboratory study included pneumococcal isolates collected during routine procedures between 2019-2025 in 27 tertiary hospitals across 17 cities in Türkiye. Identification was performed using the optochin test and bile lysis test. Serotyping was performed by the Quellung test. Antibiotic susceptibilities were tested according to the Clinical Laboratory Standards Institute (CLSI) criteria. RESULTS: Among 462 pneumococcal isolates, 72.7% were from male patients, and 43.9% were from patients aged ≥65 years. The most common diagnosis was bacteremia (55.8%), followed by pneumonia (24%) and meningitis (10.6%). The most frequent serotypes were serotype 3 (17.3%), 9N (9.1%), and 19F (5.4%). Vaccine serotype coverage rates were 34.6%, 35.9%, 47.8%, and 59.5% for PCV13, PCV15, PCV20, and PPSV23, respectively; with significantly higher coverage among patients aged ≥65 years. Most isolates were susceptible to penicillin (96.3%) and cefotaxime (97.8%) using non-meningitis breakpoints. Moxifloxacin susceptibility was 99.1%. Erythromycin resistance increased from 33.3% in 2019 to 57.5% in 2025. CONCLUSIONS: Serotype 3 was the predominant serotype. PCV20 may provide broader coverage than PCV13, particularly in older adults. Ongoing pneumococcal surveillance and rational antibiotic use remain essential.