Worms fed diets of GD1 or AN120 E. coli have decreased amounts of gut colonization as compared to worms fed OP50 or AN180 E. coli. (A) Worms were fed OP50, AN180, GD1, or AN120 E. coli strains carrying a GFP-expressing plasmid from the hatchling stage and imaged at day two, five, ten and fourteen of adulthood. Images taken at days two and five were at 100 ms exposure, and images taken at days ten and fourteen at 50 ms exposure. (B) The percent of animals showing the absence (white bar) or presence of GFP-carrying E. coli in either the pharynx only (grey bar), or in both the gut and the pharynx (black bar), was determined at the indicated times. There were no animals with fluorescence in the gut only. The number of total animals scored (n) is indicated in parentheses. Data were subjected to Chi-squared analysis, with pairwise comparisons. Asterisks indicate *p-value < 0.05 or **p-value < 0.0001 as compared with age-matched OP50-fed worms; n.s., not significant. Pairwise comparisons were also performed for each of the ages sampled across the different diets (Additional file 4).