Bacterial traits that contribute to disease are termed 'virulence factors' and there is much interest in therapeutic approaches that disrupt such traits. However, ecological theory predicts disease severity to be multifactorial and context dependent, which might complicate our efforts to identify the most generally important virulence factors. Here, we use meta-analysis to quantify disease outcomes associated with one well-studied virulence factor - pyoverdine, an iron-scavenging compound secreted by the opportunistic pathogen Pseudomonas aeruginosa. Consistent with ecological theory, we found that the effect of pyoverdine, albeit frequently contributing to disease, varied considerably across infection models. In many cases its effect was relatively minor, suggesting that pyoverdine is rarely essential for infections. Our work demonstrates the utility of meta-analysis as a tool to quantify variation and overall effects of purported virulence factors across different infection models. This standardised approach will help us to evaluate promising targets for anti-virulence approaches.

When is a bacterial "virulence factor" really virulent?