Streptococcus gallolyticus subsp. gallolyticus promotes colorectal tumor development
A and D. Species closely related to Sg do not promote cell proliferation. Stationary phase bacteria were added to HT29 (A) and HCT116 (D) cells, co-cultured for 24 hours and viable cell numbers enumerated. Sg, S. gallolyticus subsp. gallolyticus; Si, Streptococcus infantarius; Sm, S. gallolyticus subsp. macedonicus; Sp, S. gallolyticus subsp. pasteurianus. B and E. Promotion of cell proliferation requires stationary but not exponential phase Sg. TX20005 bacteria harvested at exponential or stationary phase of growth were added to HT29 (B) and HCT116 (E) cells and co-cultured for 24 hours. Viable cell numbers were enumerated. C and F. Promotion of cell proliferation requires direct contact between Sg and responsive cells. Stationary phase TX20005 bacteria were added to transwell inserts (0.4 μm pore) (TX20005-TW) or directly to cells and co-cultured with HT29 (C) and HCT116 (F) cells for 24 and 48 hours. Viable cell numbers were enumerated. Data are presented as the mean ± SEM. Each experiment was done with duplicate wells and was repeated at least three times. Data in panels A and D were analyzed using one-way, two-tailed ANOVA, followed by SNK test. Data in panels B and E were analyzed by unpaired, two-tailed t test, stationary phase vs. exponential phase. Data in panels C and F were analyzed using two-way, two-tailed ANOVA followed by SNK test. Significance shown in C and F is for comparison between cells co-cultured with TX2005 directly and cells cultured with TX20005-TW. *, p < 0.05; **, p < 0.01.