Fig 3.

Short-chain fatty acids increase C. difficile toxin production. Toxin activity (log₁₀ of toxin mg/mL) of C. difficile strain 630 normalized to the average C. difficile load [log₁₀(CFU/mL)] per condition, as measured by an in vitro cell assay (A) after 24 h of growth in BHI supplemented with 5 and 25 mM acetate, propionate, and butyrate (n = 21 per condition), and (B) at 6, 12, 18, and 24 h in BHI supplemented with 5 and 25 mM acetate, propionate, or butyrate; n > 6 per condition. (C) Toxin activity (log₁₀ of toxin mg/mL) of C. difficile strain 630 after 24 h in BHI with increasing concentrations of butyrate (0, 5, 10, 25, 50 mM; n > 3 per condition). (D) Log₂ fold change of tcdC and tcdR expressions in C. difficile strain 630 growing in BHI with 25 mM butyrate over without butyrate (measured at early and late log growth using RT-qPCR, n = 5 per condition). Statistical significance calculated using Dunnett’s test, *P-value <0.05; **P-value <0.01; ***P-value <0.001.