Pseudomonas aeruginosa is an opportunistic pathogen which can cause different diseases in human, animal and plants. To cause disease this pathogen uses different virulence factors such as biofilm formation, pyocyanin and elastase production that their production is under control of Quorum sensing (QS). Extracts of six plants, cardamom, stingingassa, thyme, eucalyptus, cumin, and garlic, were examined in this study for their effects on growth and virulence factor production of P. aeruginosa. Avishan, Zireh, and okaliptoos caused a significant inhibition of growth on LB-agar plates and on liquid cultures. Additionally each plant presented a distinct effect on biofilm formation. Among them, Zireh and Okaliptoos could induce biofilm formation although in their presence no pyocyanin were detected in cultures. Our results indicated that in lower dosage of Zireh and Okaliptoos, although we observed a good effect on pyocyanin production and biofilm formation but this result are contradictory with QS regulated behaviors. Further researches are necessary to investigate the role of plant extracts on P. aeruginosa metabolites.

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