Quantifying Food Intake in C. elegans

To study the effect of C. chinensis and E. ulmoides on the food intake of C. elegans, the E. coli strain OP50-GFP (CGC, Minneapolis, MN, United States) was used according to Raizen et al., (2012) (link). Extract-treated and control worms were transferred on the 7^th and 12^th day of adulthood to small agar plates seeded with a confluent lawn of OP50-GFP, and were allowed to feed for 15 min. Thereafter, about 25–30 nematodes per age and treatment were rinsed, washed in M9 buffer, moved to a 2% agarose pad on a glass slide, and anesthetized by 1 M NaN₃. The worms were photographed with an Axiolab fluorescence microscope (Carl Zeiss, Jena, Germany) equipped with a GFP filter and a ProgRes C12 digital camera (Jenoptik, Jena, Germany). Mean fluorescence intensities per single worm were quantified using the CellProfiler software (Mcquin et al., 2018 (link)). The intensity values were normalized by subtracting the green autofluorescence values measured in extract-treated and control worms of the same age, fed with standard OP50.