Carbon Source-Dependent Changes of the Structure of Streptococcus pneumoniae Capsular Polysaccharide with Serotype 6F

Abstract

The structure of the exopolysaccharide capsule of Streptococcus pneumoniae is defined by the genetic arrangement of the capsule operon allowing the unequivocal identification of the pneumococcal serotype. Here, we investigated the environment-dependent composition of the polysaccharide structure of S. pneumoniae serotype 6F. When grown in a chemically defined medium (CDM) with glucose versus galactose, the exopolysaccharide capsule of the serotype 6F strains reveals a ratio of 1/0.6 or 1/0.3 for galactose/glucose in the capsule by 1H-NMR analyses, respectively. Increased production of the capsule precursor UDP-glucose has been identified by 31P-NMR in CDM with glucose. Flow cytometric experiments using monoclonal antibodies showed decreased labelling of Hyp6AG4 (specific for serotype 6A) antibodies when 6F is grown in glucose as compared to galactose, which mirrors the 1H-NMR results. Whole-genome sequencing analyses of serotype 6F isolates suggested that the isolates evolved during two different events from serotype 6A during the time when the 13-valent pneumococcal conjugate vaccine (PCV-13) was introduced. In conclusion, this study shows differences in the capsular structure of serotype 6F strains using glucose as compared to galactose as the carbon source. Therefore, 6F strains may show slightly different polysaccharide composition while colonizing the human nasopharynx (galactose rich) as compared to invasive locations such as the blood (glucose rich).

Pneumococcal Vaccine for Adults Aged ≥19 Years: Recommendations of the Advisory Committee on Immunization Practices, United States, 2023

“…Pneumococci are classified into serotypes depending on their capsular polysaccharide, which is a main virulence factor for pneumococcus (4). At least 100 pneumococcal serotypes were documented as of 2020 (5)(6)(7). During 2018-2019, approximately 60%-75% of all IPD in adults was caused by the 24 pneumococcal serotypes that were included in the formulations of commercially available polysaccharide conjugate vaccine (PCV) or pneumococcal polysaccharide vaccine (PPSV) vaccines (i.e., PCV13, PCV15, PCV20, and PPSV23) (Figure).…”