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

Chemical-in-plug assays are commonly used to study bacterial chemotaxis, sometimes in the absence of stringent controls.

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.

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.