Surface motility (e.g. swarming motility) plays an important role in P. aeruginosa’s establishment of microcolonies and biofilm development [43] and we found that CAD affected swarming behaviour in a concentration-dependent fashion. Similar results were also observed in the study with P. fluorescens and CAD, indicating that CAD might potentially be used against biofilm-forming bacteria [27]. P. aeruginosa biofilm formation was inhibited at sub-MICs of CAD. Previous studies also reported biofilm-inhibitory activity of CAD against P. aeruginosa at sub-MICs (concentrations less than 0.1 %) [36]. In toxicological studies with rats, CAD demonstrated a lethal dose (LD50) at 1850 p.p.m. [44]. In this study, a substantially lower concentration of CAD of 5.9 mM (780 p.p.m.) showed good levels of biofilm inhibition and dispersion as well as inhibition of swarming motility for P. aeruginosa, indicating that this concentration of CAD could possibly be an acceptable physiological level.