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Updated: Feb 2, 2026
Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction
Published on: February 24, 2014
Population-level transition of capsular polysaccharide types among sequence type 1 group B Streptococcus isolates
Noriyuki Nagano1, Shota Koide1, Wataru Hayashi1
1Department of Health and Medical Sciences, Shinshu University Graduate School of Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan.
Abstract:
Over a 35-month period, group B Streptococcus isolates with reduced penicillin susceptibility (PRGBS) were detected from elderly patients at a regional hospital in Japan, accompanying population-level transition of PRGBS serotypes. The genetic relatedness of 77 non-duplicate PRGBS from 73 patients was analysed. Serotype III PRGBS predominated (16 serotype III/1 serotype Ib) in the first 9 months (period I), then 3 serotype Ib isolates appeared transiently for the next 3 months (period II), which was replaced predominantly by serotype Ia (20 serotype Ia/1 serotype III/1 non-typeable) for 9 months (period III). In the last 14 months (period IV), besides 25 serotype Ia isolates, 10 serotype III were also identified. Serotypes III and Ia isolates, belonging to ST1, shared G329V, G398A, V405A and G429D substitutions in penicillin-binding protein 2X. Of three strains subjected to whole-genome sequencing, serotype III strain SU12 (period I) had a higher degree of genomic similarity with serotype Ia strain SU97 (period III) than serotype Ib strain SU67 (period II) based on average nucleotide identity and single nucleotide polymorphisms. Analysis of the cps gene clusters and the upstream and downstream flanking sequences revealed that disruption of the hyaluronidase gene located upstream of cpsY by insertion of IS1548 was found in strain SU12, whereas ΔISSag8 was inserted between tRNA-Arg and rpsA genes located downstream of cpsL in strain SU97. Interestingly, most serotype III PRGBS re-emerging in period IV had this tRNA-Arg-ΔISSag8-rpsA region. Capsular switching and nosocomial transmission may possibly contribute to population-level serotype replacement among ST1 PRGBS isolates.
Insights
Group B Streptococcus isolates with reduced penicillin susceptibility (PRGBS) in elderly patients showed shifting serotypes over 35 months. Genetic analysis revealed capsular switching and nosocomial transmission may drive these population-level serotype replacements in ST1 PRGBS.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Group B Streptococcus (GBS) can cause serious infections, particularly in elderly patients.
- Reduced penicillin susceptibility in GBS (PRGBS) is an emerging concern.
- Understanding serotype dynamics and genetic relatedness of PRGBS is crucial for infection control.
Purpose of the Study:
- To investigate the population-level transition of PRGBS serotypes in elderly patients over a 35-month period.
- To analyze the genetic relatedness and genomic features of PRGBS isolates.
- To explore potential mechanisms driving serotype replacement.
Main Methods:
- Retrospective analysis of 77 non-duplicate PRGBS isolates from 73 elderly patients.
- Serotyping of isolates.
- Analysis of genetic relatedness using whole-genome sequencing (WGS).
- Investigation of specific genetic elements, including cps gene clusters and flanking regions.
Main Results:
- A significant shift in PRGBS serotypes was observed: Serotype III predominated initially, followed by transient serotype Ib, then predominantly serotype Ia, with a resurgence of serotype III.
- Serotype III and Ia isolates belonged to Sequence Type 1 (ST1) and shared key substitutions in penicillin-binding protein 2X.
- WGS revealed genomic similarities between serotype III and Ia strains, with distinct genetic alterations in capsular gene cluster flanking regions (e.g., IS1548 insertion in serotype III, ΔISSag8 in serotype Ia).
- The re-emergence of serotype III in the later period was associated with the tRNA-Arg-ΔISSag8-rpsA region.
Conclusions:
- Capsular switching and potential nosocomial transmission are likely drivers of population-level serotype replacement among ST1 PRGBS isolates.
- The study highlights the dynamic nature of PRGBS epidemiology and the importance of ongoing surveillance.
- Genetic modifications in flanking regions of the cps gene cluster may play a role in serotype evolution and adaptation.
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