We show that a single clinical isolate of the human opportunistic pathogen Pseudomonas aeruginosa (strain PA14), which previously was shown to be pathogenic in mice and plants, also kills Caenorhabditis elegans. The rate of PA14-mediated killing of C. elegans depends on the composition of the agar medium on which PA14 is grown. When PA14 is grown on minimal medium, killing occurs over the course of several days and is referred to as ''slow'' killing. When PA14 is grown on high-osmolarity medium, killing occurs over the course of several hours and is referred to as ''fast'' killing. Several lines of evidence, including the fact that heat-killed bacteria are still capable of fast but not slow killing of C. elegans, indicate that fast and slow killing occur by distinct mechanisms. Slow killing involves an infection-like process and correlates with the accumulation of PA14 within worm intestines. Among 10 PA14 virulence-related mutants that had been shown previously to affect pathogenicity in plants and mice, 6 were less effective in killing C. elegans under both fastand slow-killing conditions, indicating a high degree of commonalty among the P. aeruginosa factors required for pathogenicity in disparate eukaryotic hosts. Thus, we show that a C. elegans pathogenicity model that is genetically tractable from the perspectives of both host and pathogen can be used to model mammalian bacterial pathogenesis.

The human opportunistic pathogen Pseudomonas aeruginosa strain PA14 kills Caenorhabditis elegans. Using systematic mutagenesis of PA14 to identify mutants that fail to kill C. elegans and a C. elegans mutant that lacks P-glycoproteins, we identified phenazines, secreted P. aeruginosa pigments, as one of the mediators of killing. Analysis of C. elegans mutants with altered responses to oxidative stress suggests that phenazines exert their toxic effects on C. elegans through the generation of reactive oxygen species. Finally, we show that phenazines and other P. aeruginosa factors required for C. elegans killing are also required for pathogenesis in plants and mice, illustrating that this model tackles the dual challenges of identifying bacterial virulence factors as well as host responses to them.