Fig. 7: Stevioside restrained capsule-conferred resistance to host cell adherence and macrophage phagocytosis.

A Adhesion assay of S. pneumoniae D39 to A549 cells in the presence of DMSO or indicated concentrations of stevioside. Overnight-cultured A549 epithelial cells were infected with D39 at an MOI of 100 for 2 h and then rinsed, lysed with 0.1% Triton X-100 and plated on THY agar plates after dilution. The number of colony-forming units (CFU) was determined after overnight culture. Data are presented as the percentage of the initial inoculum CFU. B Phagocytosis of S. pneumoniae D39 by mouse primary peritoneal macrophages (MPMs) in the presence of DMSO or indicated concentrations of stevioside. The cells were infected with an MOI of 50 for 1 h, followed by another 1-hour incubation in gentamycin containing (100 μg/ml) medium after PBS washing. Then, cells were washed, lysed, and diluted for determination of bacterial count by microbiological plating. C Phagocytosis of S. pneumoniae D39 by RAW 264.7 cells with the addition of DMSO or indicated concentrations of stevioside. The cells were infected and treated as described above. The phagocytosis percentage of each inoculum was defined as the ratio of phagocytized bacteria to the total bacterial count determined before adding gentamicin. D Giemsa-stained RAW 264.7 cells treated and infected as described above. The bright arrows indicate the intracellular bacterial. Scale bars, 100 µm. All data from three biological replicates were presented as mean ± SD and analyzed using One-way ANOVA and Tukey’s posttest. *P < 0.05, **P < 0.01, and ns, no significance compared with the DMSO control group.