The susceptibility of Pseudomonas isolates to TTO, terpinen-4-ol, g-terpinene, cineole, a-terpineol and r-cymene was determined using a broth microdilution method based on CLSI guidelines.8 Mueller– Hinton broth (MHB; Oxoid) was supplemented with 0.002% (v/v) Tween 80 (Sigma) (MHB-T) to enhance dispersion of the TTO or components. A stock of TTO or component at twice the desired final concentration was prepared in MHB-T and mixed vigorously by vortex. This was used to prepare serial doubling dilutions in a 96-well tray over the range 0.03–8% (v/v). Overnight broth cultures of organisms in MHB were adjusted in MHB-T so that the final concentration in each well following inoculation of the microtitre tray was $5.0 · 105 cfu/mL. Inocula concentrations were confirmed by viable counts; after serial 10-fold dilution of the inoculum in sterile distilled water, four 10 mL samples from the appropriate dilution were inoculated onto well-dried blood agar plates. After incubation at 37C for 18–24 h the number of cfu was counted and the concentration of the inocula calculated. After 18 h of incu- bation of trays at 37C, the MIC was the lowest concentration of TTO that resulted in a clear well. Ten microlitres from each well was spot-inoculated onto pre-dried nutrient agar (NA) and incubated overnight at 35C to determine the MBC. The MBC was defined as the concentration of TTO or component that killed 99.9% of the inoculum. Experiments were performed at least three times and the modal value selected.