Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2023 Aug 4;19(8):e1011509.
doi: 10.1371/journal.ppat.1011509. eCollection 2023 Aug.

Effects of Capsular Polysaccharide amount on Pneumococcal-Host interactions

Jiaqi Zhu  1 , Annie R Abruzzo  1 , Cindy Wu  1 , Gavyn Chern Wei Bee  1 , Alejandro Pironti  1   2 , Gregory Putzel  1   2 , Surya D Aggarwal  1 , Hannes Eichner  1   3 , Jeffrey N Weiser  1
Affiliations

Effects of Capsular Polysaccharide amount on Pneumococcal-Host interactions

Jiaqi Zhu et al. PLoS Pathog. .

Abstract

Among the many oral streptococci, Streptococcus pneumoniae (Spn) stands out for the capacity of encapsulated strains to cause invasive infection. Spread beyond upper airways, however, is a biological dead end for the organism, raising the question of the benefits of expending energy to coat its surface in a thick layer of capsular polysaccharide (CPS). In this study, we compare mutants of two serotypes expressing different amounts of CPS and test these in murine models of colonization, invasion infection and transmission. Our analysis of the effect of CPS amount shows that Spn expresses a capsule of sufficient thickness to shield its surface from the deposition of complement and binding of antibody to underlying epitopes. While effective shielding is permissive for invasive infection, its primary contribution to the organism appears to be in the dynamics of colonization. A thicker capsule increases bacterial retention in the nasopharynx, the first event in colonization, and also impedes IL-17-dependent clearance during late colonization. Enhanced colonization is associated with increased opportunity for host-to-host transmission. Additionally, we document substantial differences in CPS amount among clinical isolates of three common serotypes. Together, our findings show that CPS amount is highly variable among Spn and could be an independent determinant affecting host interactions.

PubMed Disclaimer

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Characterization of Spn strains expressing different amounts of capsular polysaccharide phosphorylcholine.
Immunoblots of Spn lysates of serotype (A) T6A or (B) T4 strains with serotype-specific anti-capsule antibody. (C-F) Shielding effect of the capsule evaluated using quantification by flow cytometry. Binding of mAb TEPC-15 to phosphorylcholine on (C) T6A or (D) T4 strains. Deposition of complement (C3b) from normal mouse serum using anti-mouse C3 antibody on (E) T6A or (F) T4 strains. Statistical significance based on the percentage of Spn cells in which antibody binding was detected was determined using the Kruskal-Wallis test followed by Dunn’s correction. Corrected mutant (CM).
Fig 2
Fig 2. Effect of differences in CPS amount on invasive infection.
(A-B) 10-day-old pups were challenged intraperitoneally with Spn (~102 CFU) of (A) T6A or (B) T4 strains and sacrificed 24 hrs later when blood was collected for quantitative culture to determine bacterial burden in the bloodstream. Statistical significance was determined using a Kruskal-Wallis test followed by Dunn’s correction. (C-D) Pups were pretreated with either cobra venom factor (CVF) or vehicle control (PBS). Limit of detection (LOD). Statistical significance was determined using the Mann-Whitney test.
Fig 3
Fig 3. Effect of differences in CPS amount on colonization dynamics.
(A) 10-day-old pups (C57BL6) were challenged intranasally (IN) with T6A strains (~102 CFU) and sacrificed at 1 day, 3 days, 14 days, or 28 days post-infection. Upper respiratory tract (URT) lavages were collected for quantification of colonization density. Statistical significance was determined using a Kruskal-Wallis test followed by Dunn’s correction. (B) IL17ra-/- pups at 10 days of age were challenged IN with T6A strains (~102 CFU) and sacrificed at 1 day or 28 days post-infection. URT lavages were collected for quantification of colonization density. Statistical significance was determined using the Mann-Whitney test. (C) C57BL6 pups at 4 days of age were challenged IN with T4 strains (~102 CFU) and sacrificed at 1 day, 3 days, 14 days, or 28 days post-infection. URT lavages were collected for quantification of colonization densities. Statistical significance was determined using a Kruskal-Wallis test followed by Dunn’s correction. Limit of detection (LOD).
Fig 4
Fig 4. Effect of differences in CPS amount on retention of the inoculum.
Pups at 10 (T6A) or 5 (T4) days of age were challenged intranasally with Spn (~102−3 CFU) strains (A) T6A or (B) T4. The pups were sacrificed 4 hours after infection to obtain URT lavages for quantitative culture. Limit of detection (LOD). Statistical significance was determined using Kruskal-Wallis test followed by Dunn’s correction. (C) Competition assay of T6A strains. Pups at 5–10 days of age were challenged IN (~102−3 CFU/strain) with an equal mixture of the two strains indicated below and sacrificed 4 hours later. URT lavages were collected for quantitative culture with strains distinguished by colony morphology. Values represent the ratio of strains in the lavage (output) over the ratio in the inoculum (input) for each pup. Statistical significance was determined using the Mann-Whitney test in comparison to a hypothetical value of 1 (representing no competition).
Fig 5
Fig 5. CPS amount affects sepsis following colonization.
10-day-old pups were challenged intranasally with T6A strains (~102 CFU) and survival monitored for 14 days. Statistical significance was determined using the Kaplan-Meier test followed by Dunn’s correction. n = 22-41/group.
Fig 6
Fig 6. Variation in CPS amount among clinical isolates.
Clinical isolates from our collection (labelled by strain P#) of three CPS types (6A, 6B, 23F) were grown to mid-log phase and a lysate adjusted for equal loading was applied to a nitrocellulose membrane. CPS was detected with type-specific antisera and relative binding compared in relation to a standard curve generated using purified CPS of the same type (shown boxed with amount loaded indicated) and quantified by densitometry. The level of CPS of each isolate is expressed relative to the strain of the same type with the least CPS (1x). An unencapsulated mutant served as negative control (Δcps).
Fig 7
Fig 7. Analysis of a clinical isolate.
(A)10-day-old pups were challenged intraperitoneally (102 CFU) and sacrificed 24 hrs later when blood was collected for quantitative culture. Strains included the clinical isolate P592 and P2797, an opaque variant obtained from the bloodstream of a pup challenged with P592 at a high dose. (B) Immunoblots of lysates with serotype 6A-specific anti-capsule antibody. Comparison to a standard curve generated using type 6A CPS was used to compare the relative amount of CPS in P2797 compared to the parent P592. (C) Pups at 10 days of age were challenged IN with 102−3 CFU of the strain indicated. URT lavages were collected at 3 days post-infection for quantification of colonization density. Statistical significance was determined using the Mann-Whitney test.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. Collaborators AR. Global burden of bacterial antimicrobial resistance in 2019: a systematic analysis. Lancet. 2022;399:629–55. doi: 10.1016/S0140-6736(21)02724-0 - DOI - PMC - PubMed
    1. Weiser J, Ferreira D, Paton J. Streptococcus pneumoniae: transmission, colonization and invasion. Nat Rev Microbiol. 2018;16:355–67. doi: 10.1038/s41579-018-0001-8 - DOI - PMC - PubMed
    1. Watson D, Musher D. Interruption of capsule production in Streptococcus pneumonia serotype 3 by insertion of transposon Tn916. Infect Immun. 1990;58:3135–8. doi: 10.1128/iai.58.9.3135-3138.1990 - DOI - PMC - PubMed
    1. Paton J, Trappetti C. Streptococcus pneumoniae Capsular Polysaccharide. Microbiol Spectr. 2019;7: doi: 10.1128/microbiolspec.GPP3-0019-2018 - DOI - PubMed
    1. Hyams C, Camberlein E, Cohen J, Bax K, Brown J. The Streptococcus pneumoniae capsule inhibits complement activity and neutrophil phagocytosis by multiple mechanisms. Infect Immun. 2010;78(704–715). doi: 10.1128/IAI.00881-09 - DOI - PMC - PubMed

Publication types

Substances