The chemical-in-plug bacterial chemotaxis assay is prone to false positive responses

BACKGROUND: Chemical-in-plug assays are commonly used to study bacterial chemotaxis, sometimes in the absence of stringent controls. RESULTS: We report that non-chemotactic and non-motile mutants in two distinct bacterial species (Shewanella oneidensis and Helicobacter pylori) show apparent zones of accumulation or clearing around test plugs containing potential attractants or repellents, respectively. CONCLUSIONS: Our results suggest that the chemical-in-plug assay should be used with caution, that non-motile or non-chemotactic mutants should be employed as controls, and that results should be confirmed with other types of assays.