Figure 3. Serotonin-induced feeding did not improve intestinal lumen colonization by Bp R15. (A) The efficacy of 5 mM serotonin toward feeding stimulation is shown by the significant increase in pharyngeal pumping rates in worms exposed to R15-GFP. Bars correspond to pharyngeal pumping mean ± SEM (pump/sec for each worm) (n = 30). **p < 0.01, ***p < 0.001 (Student’s t-test). (B) Defecation rates of infected worms were not significantly affected by the addition of 5 mM serotonin into the assay medium. Bars correspond to the mean ± SD of Exp/5 min for each worm (n = 3). (C) Despite increased feeding rates, the number of colonizing R15-GFP did not change significantly within the serotonin-induced infected worms. Each marker corresponds to the average bacterial CFU of 10 infected worms; horizontal lines represent the geometric means of CFU. Graphs (B and C) were analyzed using the Mann-Whitney U-test. Graphs (A–C) share the same labels: white bar, N2 worms fed on E. coli OP50; gray bars/circles, worms infected with R15-GFP; black bars/triangles, serotonin-induced worms exposed to R15-GFP. Abbreviations: 5-HT, 5-hydroxytryptamine or serotonin; n.s., not significant.