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Genetic relatedness within serotypes of penicillin-susceptible Streptococcus pneumoniae isolates
K Overweg1, D Bogaert, M Sluijter
1Department of Pediatrics, Sophia Children's Hospital, Erasmus University Rotterdam, Rotterdam, The Netherlands.
Abstract:
The molecular epidemiological characteristics of all Streptococcus pneumoniae strains isolated in a nationwide manner from patients with meningitis in The Netherlands in 1994 were investigated. Restriction fragment end labeling analysis demonstrated 52% genetic clustering among these penicillin-susceptible strains, a value substantially lower than the percentage of clustering among Dutch penicillin-nonsusceptible strains. Different serotypes were found within 8 of the 28 genetic clusters, suggesting that horizontal transfer of capsular genes is common among penicillin-susceptible strains. The degree of genetic clustering was much higher among serotype 3, 7F, 9V, and 14 isolates than among isolates of other serotypes, i.e., 6A, 6B, 18C, 19F, and 23F. We further studied the molecular epidemiological characteristics of pneumococci of serotype 3, which is considered the most virulent serotype and which is commonly associated with invasive disease in adults. Fifty epidemiologically unrelated penicillin-susceptible serotype 3 invasive isolates originating from the United States (n = 27), Thailand (n = 9), The Netherlands (n = 8), and Denmark (n = 6) were analyzed. The vast majority of the serotype 3 isolates (74%) belonged to two genetically distinct clades that were observed in the United States, Denmark, and The Netherlands. These data indicate that two serotype 3 clones have been independently disseminated in an international manner. Seven serotype 3 isolates were less than 85% genetically related to the other serotype 3 isolates. Our observations suggest that the latter isolates originated from horizontal transfer of the capsular type 3 gene locus to other pneumococcal genotypes. In conclusion, epidemiologically unrelated serotype 3 isolates were genetically more related than those of other serotypes. This observation suggests that serotype 3 has evolved only recently or has remained unchanged over long periods.
Insights
Molecular epidemiology reveals two dominant Streptococcus pneumoniae serotype 3 clones spread internationally. Penicillin-susceptible strains show more genetic diversity and gene transfer than resistant ones.
Area of Science:
- Microbiology
- Epidemiology
- Molecular Biology
Background:
- Streptococcus pneumoniae causes meningitis, a serious infection.
- Understanding pneumococcal strain characteristics is crucial for public health.
- Penicillin resistance in Streptococcus pneumoniae is a growing concern.
Purpose of the Study:
- To investigate the molecular epidemiology of Streptococcus pneumoniae strains causing meningitis in the Netherlands in 1994.
- To compare genetic clustering between penicillin-susceptible and penicillin-nonsusceptible strains.
- To analyze the molecular characteristics of the virulent serotype 3 of Streptococcus pneumoniae.
Main Methods:
- Restriction fragment end labeling analysis was used to assess genetic relatedness.
- Nationwide isolation of Streptococcus pneumoniae strains from meningitis patients.
- Comparative analysis of serotype 3 isolates from multiple countries.
Main Results:
- 52% genetic clustering was observed among penicillin-susceptible strains, lower than penicillin-nonsusceptible strains.
- Horizontal gene transfer of capsular genes is common in penicillin-susceptible strains.
- Two distinct serotype 3 clones were identified, showing international dissemination, with some isolates suggesting horizontal gene transfer.
Conclusions:
- Serotype 3 Streptococcus pneumoniae isolates are more genetically related than other serotypes, suggesting recent evolution or long-term stability.
- International dissemination of specific pneumococcal clones is evident.
- Genetic diversity and horizontal gene transfer play significant roles in pneumococcal epidemiology.