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Competition among Streptococcus pneumoniae for intranasal colonization in a mouse model
M Lipsitch1, J K Dykes, S E Johnson
1Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. mlipsitc@hsph.harvard.edu [corrected]
Vaccine
|May 17, 2000
Summary
Pneumococcal conjugate vaccines may increase non-vaccine serotype carriage. Mouse models show vaccine-type Streptococcus pneumoniae can inhibit non-vaccine type acquisition, supporting serotype replacement theories.
Area of Science:
- Microbiology
- Immunology
- Epidemiology
Background:
- Pneumococcal conjugate vaccines reduce carriage of targeted Streptococcus pneumoniae serotypes.
- Serotype replacement, an increase in non-vaccine serotypes, is a potential consequence of widespread vaccination.
- Mathematical models suggest inter-serotype inhibition influences the extent of serotype replacement.
Purpose of the Study:
- To investigate if carriage of one Streptococcus pneumoniae serotype inhibits the acquisition of other serotypes in a mouse model.
- To provide empirical evidence for assumptions used in mathematical models of pneumococcal serotype replacement.
Main Methods:
- A mouse model of intranasal Streptococcus pneumoniae carriage was employed.
- Mice were colonized with a resident strain (serotype 6B) and challenged with different serotypes.
- Inhibition of colonization was assessed by comparing bacterial loads after challenge.
Main Results:
- Carriage of a vaccine-type (6B) Streptococcus pneumoniae strain reduced colonization by challenge strains (same and 23F serotypes).
- This inhibition effect could be overcome by increasing the challenge dose.
- Conversely, carriage of a non-vaccine type strain (23F) did not inhibit acquisition of the vaccine-type strain.
Conclusions:
- The study provides evidence for biological mechanisms underlying pneumococcal serotype replacement.
- Findings support the hypothesis that competition between Streptococcus pneumoniae serotypes contributes to vaccine-induced shifts in carriage.
- These results validate key assumptions in mathematical models predicting serotype replacement dynamics.