The main aims of this study were (1) to identify and compare the major biologically active compounds in the metabolome of ligulate and tubular flowers of two C. officinalis cultivars, ‘Golden Sea’ (GS) and ‘Paradise Garden’ (PG), and (2) to investigate the effect of different proportions of ligulate and tubular flowers in the inflorescences on their metabolome. Ultra-performance liquid chromatography with photodiode array detection and a Q Exactive Orbitrap high-resolution mass spectrometer were used to analyse the flower metabolome. Analysis of the metabolomics data revealed that polar lipids showed the most significant differences between flowers. Tubular flowers of PG and GS cultivars contained higher levels of 31 and 34 out of 36 lipids, respectively. Furthermore, tubular flowers of both cultivars contained significantly higher levels of phenolamides and caffeoylquinic acids, but lower levels of triterpenoids. To compare the metabolite content of the two C. officinalis cultivars, we analysed the data for their inflorescences. The study showed that GS inflorescences contained significantly higher levels of phenolic compounds and lipids than PG inflorescences. This GS advantage was due to two factors: firstly, the higher content of these metabolites in tubular flowers and, secondly, the higher proportion of tubular flowers in GS inflorescences.

Streptococcus pneumoniae causes invasive infections such as otitis media, pneumonia and meningitis. It produces pneumolysin (Ply) toxin, which forms a pore to host cell membrane and has multiple functions in S. pneumoniae pathogenesis. The Ply C-terminal domain 4 mediates binding to membrane cholesterol and induces the formation of pores composed of up to 40 Ply monomers. Ply has a key role in the establishment of nasal colonization, pneumococcal transmission from host to host and pathogenicity. Altogether, 27 hydrolyzable tannins were tested for Ply inhibition in hemolysis assay and tannin-protein precipitation assay. Pentagalloylglucose (PGG) and gemin A showed nanomolar inhibitory activity. Ply oligomerization on the erythrocyte surface was inhibited with PGG. PGG also inhibited Ply cytotoxicity to A549 human lung epithelial cells. Molecular modelling of Ply interaction with PGG suggested that it binds to the pocket formed by domains 2, 3 and 4. In this study, we reveal the structural features of hydrolyzable tannins that are required for interaction with Ply. Monomeric hydrolysable tannins containing a sufficient number of polyvalent and flexible galloyl groups have highest inhibitory power to Ply cytotoxicity, and are followed by oligomers. Of the oligomers, macrocyclic and C-glycosidic structures were weaker in their inhibition than the glucopyranose-based oligomers. Accordingly, PGG-type monomers and certain oligomers might have therapeutic value in the targeting of S. pneumoniae infections.