In-vitro antimicrobial activity of new antimicrobial agents against Streptococcus pneumoniae and potential resistance mechanisms: a multicenter study.

Background: Streptococcus pneumoniae is a major cause of invasive and non-invasive diseases, particularly in children and immunocompromised individuals, with an annual mortality of approximately 800,000 children worldwide. The rise of antibiotic-resistant strains complicates treatment, especially with increasing resistance to penicillin, macrolides, and fluoroquinolones. The study on the resistance of newly developed antimicrobial agents against S. pneumoniae was rarely reported. Furthermore, understanding the relationship between serotypes, resistance mechanisms, and virulence in S. pneumoniae is essential for disease management and vaccine development.

Methods: A total of 208 S. pneumoniae isolates were collected across nine hospitals in seven Chinese cities/provinces from January 2023 to June 2024. Molecular characteristics were analyzed using whole-genome sequencing to identify serotypes, sequence types, virulence genes, and potential resistance mechanisms. Antibiotic susceptibility test (AST) was performed against 14 agents, involving new antibiotics (eravacycline, omadacycline, nemonoxacin, and contezolid).

Results: Serotypes 19 F (24.6%) and 23 F (11.1%) predominated, with vaccine coverage rates of PCV13 at 66.8%. High resistance rates in S. pneumoniae were observed for erythromycin (208/208, 100%), clindamycin (197/208, 94.7%), and tetracycline (192/208, 92.3%). 13.5% (28/208) and 2.9% (6/208) strains were intermediate and resistant to penicillin, respectively. The new antibiotics showed low resistance, namely, 1.9% (4/208), 0.5% (1/208), 1.9% (4/208), and 7.2% (15/208) resistant to eravacycline, omadacycline, contezolid, and nemonoxacin, respectively. Resistance mechanisms included mutations in 23S rRNA for oxazolidinones, tet genes for tetracyclines, and gyrA/parC for fluoroquinolones.

Conclusions: S. pneumoniae in China exhibits high genetic diversity and significant antibiotic resistance, underscoring the need for continuous surveillance and updated vaccines. New antibiotics remain effective against multidrug-resistant strains, offering potential treatment options in clinical settings.