Bacteriological characteristics and changes of Streptococcus pneumoniae serotype 35B after vaccine implementation in Japan
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Updated: Jun 11, 2025
Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43
Published on: September 11, 2020
Haruko Miyazaki1, Bin Chang2, Michinaga Ogawa2
1Department of Microbiology, Tokyo Medical University, Tokyo, Japan.
Abstract:
Streptococcus pneumoniae serotype 35B, a non-vaccine type, is a major contributor to the increase in pneumococcal infection post-vaccination. We aimed to understand the mechanism of its spread by characterizing 35B. The serotype, type 1 pilus (T1P) positivity, and antimicrobial susceptibility of 319 isolates in 2018-2022 were analysed and compared with those of isolates in 2014-2017 to find the changes. 35B accounted for 40 (12.5%) isolates. T1P positivity was notably higher in 35B (87.5%) than in the other serotypes. To confirm the role of T1P, an adhesion factor, we compared adherence to A549 cells between T1P-positive 35B isolates and their T1P-deficient mutants, showing contribution of T1P to adherence. Penicillin-non-susceptible rate of 35B was 87.5%, and meropenem-resistant 35B rate was 35.0%, which increased from 14.5% of 2014-2017 (p = 0.009). Multilocus sequence typing was performed in 35B strains. Prevalence of clonal complex 558, harbouring T1P and exhibiting multidrug non-susceptibility, suggested the advantages of 35B in attachment and survival in the host. The emergence of ST156 isolates, T1P-positive and non-susceptible to β-lactams, has raised concern about expansion in Japan. The increase of serotype 35B in pneumococcal diseases might have occurred due to its predominant colonizing ability after the elimination of the vaccine-serotypes.
Insights
Streptococcus pneumoniae serotype 35B, a non-vaccine type, is increasing due to its enhanced ability to attach, facilitated by type 1 pilus (T1P). This serotype also shows concerning antimicrobial resistance, particularly to meropenem.
Area of Science:
- Microbiology
- Infectious Diseases
- Genetics
Background:
- *Streptococcus pneumoniae* serotype 35B is a non-vaccine type contributing to increased pneumococcal infections post-vaccination.
- Understanding the spread mechanisms of serotype 35B is crucial for public health interventions.
Purpose of the Study:
- To characterize *Streptococcus pneumoniae* serotype 35B isolates to understand their increasing prevalence.
- To investigate the role of type 1 pilus (T1P) in the adherence and spread of serotype 35B.
- To assess antimicrobial susceptibility patterns and genetic relatedness of serotype 35B strains.
Main Methods:
- Analysis of 319 *Streptococcus pneumoniae* isolates from 2018-2022, comparing serotype, T1P positivity, and antimicrobial susceptibility with 2014-2017 data.
- In vitro adherence assays comparing T1P-positive 35B isolates with T1P-deficient mutants using A549 cells.
- Multilocus sequence typing (MLST) of serotype 35B strains.
Main Results:
- Serotype 35B accounted for 12.5% of isolates, with significantly higher T1P positivity (87.5%) compared to other serotypes.
- T1P was confirmed to contribute to the adherence of 35B to A549 cells.
- High rates of penicillin non-susceptibility (87.5%) and a concerning increase in meropenem resistance (35.0%) were observed in 35B.
- MLST identified clonal complex 558, associated with T1P and multidrug resistance, suggesting advantages in host attachment and survival.
- Emergence of T1P-positive, beta-lactam non-susceptible ST156 isolates raises concerns for expansion in Japan.
Conclusions:
- Type 1 pilus (T1P) enhances the colonization and adherence of *Streptococcus pneumoniae* serotype 35B, contributing to its increased prevalence.
- The rising antimicrobial resistance, particularly to meropenem, in serotype 35B is a significant public health concern.
- Specific clonal complexes, like CC558 and ST156, possess advantageous traits for spread and survival, necessitating enhanced surveillance.
