Live C. burnetii accumulates in the intestinal lumen of C. elegans and generates Elbs after 8 d exposure. (a, b) Nematodes fed live E. coli CEC and observed by microscopy after 8 d consistently showed that C. elegans completely digested E. coli without signs of intestinal distension (arrowheads). (c, d) In contrast, nematodes fed live C. burnetii CCB and observed 8 d later exhibited an intense mCherry signal that was mainly restricted to the intestinal lumen. Additionally, Elb pathology was occasionally evident, suggesting colonization of luminal epithelial cells by C. burnetii. Elbs were not evident in (a, b) worms fed live CEC or dead CCB (not shown). Images were acquired at the same exposure time and joined and oriented with worm anteriors at the top. Bar =50 μM. PIV: pharyngeal–intestinal valve; An: anus; PC: phase contrast; mCh: fluorescent mCherry signal.