FIG. 2.

The mechanism of S. flexneri-mediated C. elegans killing is distinct from that of S. enterica and P. aeruginosa. (A) Young adult hermaphrodite nematodes were fed on lawns of either E. coli OP50 (squares) or S. flexneri 2457T (closed circles) continuously or fed on S. flexneri 2457T for 24 h and then transferred to OP50 for the duration of the assay (open circles). Nematodes were scored daily for survival. The survival curve represents data from three independent experiments, each using 20 nematodes. (B) The time required for nematodes to die (TD₅₀) was calculated from the survival data in panel A, representing data from three independent experiments. Asterisks indicate significant differences, compared to results for OP50 (P < 0.05). (C) Young adult hermaphrodite nematodes were fed on E. coli DH5α-GFP (squares), S. flexneri 2457T-GFP (circles), or S. enterica serovar Typhimurium SL1344-GFP (asterisks) for 24 h and then transferred to lawns of E. coli OP50. Nematodes were removed every 24 h and mechanically disrupted to release internalized bacteria. Diluted lysates were plated on LB-ampicillin plates, and colonies were scored in order to quantify S. flexneri cells associated with individual nematodes. (D) Young adult hermaphrodites were fed on either live or UV-killed E. coli OP50 or S. flexneri 2457T and scored daily for survival. The time for nematodes to die (TD₅₀) was calculated from the survival data. Asterisks indicate significant differences, compared to results for OP50 (P < 0.05). (E) Young adult nematodes were fed on either E. coli OP50 or S. flexneri 2457T or on E. coli OP50 plated on agar plates incubated with E. coli OP50 or S. flexneri 2457T separated by a 0.45-μm filter. The nematodes were scored daily for survival, and the time required for nematodes to die (TD₅₀) was calculated from the survival data. Asterisks indicate significant differences, compared to results for OP50 (P < 0.05).