2618. Determination of the Chemical Structure of a Novel Pneumococcal Serotype, 39X

BACKGROUND: Streptococcus pneumoniae produces a diverse group of capsular polysaccharides (serotypes) that are important for the virulence of the organism and for the serotype-specific prevention of pneumococcal disease. As a consequence of widespread PCV usage and pneumococcal genome plasticity, the distribution of pneumococcal serotypes is changing with an increase in non-vaccine serotypes post-vaccine introduction, a phenomenon known as serotype replacement. Recently, a potentially novel serotype was described and was provisionally named as serotype 39X. Genetic studies suggest that this novel serotype may be a hybrid of serotypes 6C and 39/10A. METHODS: Three 39X strains with the distinct serological and genetic description of the cps biosynthetic loci were obtained from the Global Pneumococcal Sequencing project (www.pneumogen.net). Capsular polysaccharide from one (Camb.853/MNZ2334) of the 39X strains was purified by sequential ethanol precipitation followed by ion-exchange chromatography. To detect polysaccharide fractions during purification, an inhibition ELISA assay was developed using factor serum 10d. The chemical structure of the 39X repeating unit was determined using one-dimensional (1D) and 2D nuclear magnetic resonance (NMR). RESULTS: All three isolates were confirmed to have the 39X genotype by PCR amplification and sequencing of the 39X specific region (wciN(6c)-wcrO-wcrC(39)) of the cps locus. (Figure 1). The 39X capsule PS fractions were detected during purification and pooled for structural studies (Figure 2). 1D-NMR for 39X showed it to be chemically distinct (Figure 3). 2D-NMR studies revealed that five of the sugar residues in 39X PS are identical to those in 39 PS, except the acetylation (Figure 4). The remaining part of the structure is being investigated. CONCLUSION: The 39X capsular PS has a distinct chemical structure in addition to its distinct serologic and genetic properties. Given that serotype 39X is a new serotype, it becomes the 100th pneumococcal serotype. The chemical structure supports the genetic depiction of serotype evolution as a result of recombination between well-characterized and unrelated serotypes. Structural elucidation of the 39X capsule PS will help facilitate our understanding of serotype replacement and vaccine development. [Image: see text] [Image: see text] [Image: see text] [Image: see text] DISCLOSURES: All authors: No reported disclosures.