Objective:To analyze the epidemiological characteristics，antibiotic resistance，and genomic features of Streptococcus pneumonia（ S. pneumoniae）in children aged ≤5 years with community-acquired pneumonia（CAP）in Liaocheng，Shandong Province. Methods:From January 2020 to December 2024，136 S. pneumoniae strains were isolated from sputum or nasopharyngeal swab samples of CAP patients aged ≤5 years. Whole-genome sequencing and antimicrobial susceptibility testing were performed. Serotyping，multilocus sequence typing，and Global Pneumococcal Sequence Clusters were analyzed using the Pathogenwatch platform. Antimicrobial resistance genes and virulence genes were identified via the CARD and VFDB databases，respectively. Phylogenetic analysis was conducted based on single-copy core proteins. Additionally，pharyngeal swabs from 218 healthy children aged ≤5 years in a kindergarten of Liaocheng，were collected to detect S. pneumoniae carriage. Results:Among the 136 S. pneumoniae isolates，the predominant serotypes were 19F，23F，3，6A，and 19A. The dominant sequence types（STs）were ST271，ST320，and ST505，with GPSC1（35.29%，48/136）and GPSC12（7.35%，10/136）being identified as the most prevalent clusters. Core genome phylogenetic analysis revealed that the serotype distribution of S. pneumoniae was associated with both the evolutionary relationships and STs of the strains. Specifically，a single serotype generally corresponded to multiple STs，while strains with the same ST clustered within the same clade or closely related branches on the phylogenetic tree. All isolates were multidrug-resistant，showing high resistance rates to erythromycin（100.00%），clindamycin（97.79%，133/136），and tetracycline（97.06%，132/136）. Resistance genes patA， pmrA， tetM，and ermB were detected in 100.00% of isolates，while patB and RlmA（Ⅱ） were present in 99.26%（135/136）. Virulence genes cbpG， pavA， lytA， nanA， cps4A and cps4B were detected in all isolates（100.00%）. Notably，94.12%（48/51）of serotype 19F and 19A isolates carried both pilus-1 and pilus-2 genes. Among healthy children，29.36%（64/218）were carriers of S. pneumoniae. Conclusions:There is a correlation between serotypes and phylogenetic evolution of S. pneumoniae among children with CAP in this region. Strains are predominantly of serotype 19F，exhibiting a high prevalence of multidrug resistance. These results highlight the urgency of implementing evidence-based interventions，including standardized antimicrobial stewardship programs，expanding the coverage of pneumococcal conjugate vaccine immunization，and establishing robust genomic surveillance systems，to curb the transmission of multidrug-resistant S.pneumoniae strains and improve clinical outcomes in pediatric populations.
(8.0+极速模式)