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. 2025 Mar 25;17(1):7.
doi: 10.1186/s41479-025-00162-2.

Streptococcus pneumoniae serotype 33H: a novel serotype with frameshift mutations in the acetyltransferase gene wciG

Sam Manna  1   2   3 , Belinda D Ortika  4 , Joel P Werren  5 , Casey L Pell  4 , Ilche Gjuroski  6 , Stephanie W Lo  7   8 , Jason Hinds  9   10 , Odgerel Tundev  11 , Eileen M Dunne  12 , Bradford D Gessner  12 , Fiona M Russell  4   13 , E Kim Mulholland  4   14 , Tuya Mungun  11 , Claire von Mollendorf  4   13 , Stephen D Bentley  8 , Markus Hilty #  5 , Neil Ravenscroft #  15 , Catherine Satzke #  4   13   16
Affiliations

Streptococcus pneumoniae serotype 33H: a novel serotype with frameshift mutations in the acetyltransferase gene wciG

Sam Manna et al. Pneumonia (Nathan). .

Abstract

Background: Streptococcus pneumoniae (the pneumococcus) is a leading cause of community-acquired pneumonia. Pneumococci are categorised into serotypes, based on the type of capsular polysaccharide produced, which has important implications for virulence, vaccine impact and global surveillance. Recently, we identified a novel serotype, which we named 33G, that is comprised of an O-acetylated hexasaccharide repeat unit. In this study, we report and describe variants of 33G, designated 33G-like, which we isolated from the nasopharynx of two adults hospitalised with pneumonia in Mongolia.

Methods: Serological comparison of 33G and 33G-like pneumococci were conducted by Quellung serotyping. Genetic analysis of the capsular polysaccharide loci was performed using whole genome sequencing. Polysaccharide composition was determined using 1H nuclear magnetic resonance.

Results: By Quellung serotyping, 33G pneumococci type as both 10B and 33B whereas 33G-like pneumococci type as both 10B and 33F. Genomic analysis of the capsular polysaccharide locus revealed 33G-like loci are identical to 33G, except for frameshift mutations in the wciG gene which encodes an acetyltransferase responsible for the O-acetylation of beta-galactofuranose (β-Galf) in the capsular polysaccharide repeat unit. We constructed an artificial 33G-like by deleting wciG in a 33G strain and confirmed this gene was responsible for the serological differences between 33G and 33G-like pneumococci. Lastly, 1H nuclear magnetic resonance confirmed the O-acetylation present in the 33G polysaccharide is absent in the 33G-like polysaccharide.

Conclusions: Here, we have provided serological, genetic and biochemical evidence that the 33G-like capsule differs to 33G and all other pneumococcal serotypes, meeting the requirements to be designated as a new serotype, which we have named 33H.

Keywords: Streptococcus pneumoniae; Capsule; Serotypes, vaccines.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: The 33G-like isolates described in this study were derived from a hospital-based pneumonia surveillance program of adults in Mongolia, which involved collection of nasopharyngeal swabs for pneumococcal detection and serotyping. Further details of the study protocol have been described previously [12]. Study approval was obtained from the National Ethics Committee for Health Research in Mongolia as well as the Royal Children’s Hospital Human Research Ethics Committee in Australia (HREC number 38045B). Written informed consent was acquired from all participants prior to study enrolment. Consent for publication: Not applicable. Competing interests: CVM, EKM, TM, BDG, and CS are investigators on a clinical research collaboration with Pfizer on PCV vaccination in Mongolia from which the isolates used in this study are derived. Salary support was received through the institutions. CS and EKM are investigators on a Merck Investigator Studies Program grant funded by MSD for a study unrelated to this work. SM, CVM, and CS have received honoraria [Pfizer (CS, SM, and CVM) and MSD (CS)] for presentations at symposia or attendance at expert advisory meetings unrelated to this study. MH is an investigator on a research grant funded by Pfizer for a study unrelated to this work. EMD and BDG are employed by Pfizer and may hold Pfizer stock or stock options. JH is co-founder and shareholder of BUGS Bioscience Ltd., a not-for-profit spin-out company of St George’s, University of London.

Figures

Fig. 1
Fig. 1
Schematic comparison of the 33G and 33G-like cps loci. Shading indicates DNA sequence identity (%). The light grey cross indicates a related sequence between orf1 and wzx, which may be a remnant of the recombination event that gave rise to the 33G cps locus. Image was created using Easyfig version 2.2.5 [28]. For full DNA sequence alignments, see Supplementary Figs. 1 and 2
Fig. 2
Fig. 2
1H diffusion-ordered spectroscopy (DOSY) NMR spectra of 33G (A), 33G-like (B-C) and artificial 33G-like (D) pneumococcal isolates identified in this study compared with the 33G polysaccharide spectrum reported previously (E) [2] at 500 MHz and 25 °C. CWPS = cell wall polysaccharide. Highlighted areas denote the location of acetylation peaks
Fig. 3
Fig. 3
Polysaccharide repeat unit structure of 33G [2] and the new serotype 33H (33G-like) identified in this study. Enzymatic assignments have been designated based on the literature [29]
See this image and copyright information in PMC

References

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