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The chemical composition of three Citrus limon oils: lemon essential oil (LEO), lemon terpenes (LT) and lemon essence (LE), and their influence in the virulence factors production and motility (swarming and swimming) of two Pseudomonas aeruginosa strains (ATCC 27853 and a multidrug-resistant HT5) were investigated. The main compound, limonene, was also tested in biological assays. Eighty-four compounds, accounting for a relative peak area of 99.23%, 98.58% and 99.64%, were identified by GC/MS. Limonene (59-60%), γ -terpinene (10-11%) and β -pinene (7-15%) were the main compounds. All lemon oils inhibited specific biofilm production and bacterial metabolic activities into biofilm in a dose-dependent manner (20-65%, in the range of 0.1-4 mg mL -1 ) of both strains. Besides, all samples inhibited about 50% of the elastase activity at 0.1 mg mL -1 . Pyocyanin biosynthesis decreases until 64% (0.1-4 mg mL -1 ) for both strains. Swarming motility of P. aeruginosa ATCC 27853 was completely inhibited by 2 mg mL -1 of lemon oils. Furthermore, a decrease (29-55%, 0.1-4 mg mL -1 ) in the synthesis of Quorum sensing (QS) signals was observed. The oils showed higher biological activities than limonene. Hence, their ability to control the biofilm of P. aeruginosa and reduce the production of virulence factors regulated by QS makes lemon oils good candidates to be applied as preservatives in the food processing industry.

Citrus essential oils are used in food to confer flavor and aromas. The citrus essential oils have been granted as GRAS and could be used as antimicrobial additives to control bacterial quorum sensing from potential food bacterial pathogens. The chemical composition and inhibitory activity of Citrus paradisi (grapefruit) essential oils obtained by cold-pressed method (EOP) and cold-pressed method followed by steam distillation, against Pseudomonas aeruginosa were determined . The GC-MS analyses of the oil indicated the amount of the essential oil components was highest with D-limonene in both cases. However, the extraction method modified the chemical composition. EOP had higher amount of coumarins and flavonoid as well as less oxygenated terpenoids. At 0.1 mg/mL essential oils were not able to modify the bacterial development but inhibited the P. aeruginosa biofilm production between 52% and 55%, sessile viability between 45% and 48%, autoinducer production and elastase activity between 30% and 56%. Limonene was less effective at inhibiting P. aeruginosa than the essential oils, suggesting a synergistic effect of the minor components. According to our results, grapefruit essential oils could be used as a food preservative to control P. aeruginosa virulence.

Sixteen plant sesquiterpene lactones, thirteen from four species of the Family Asteraceae, and three from a species of Hepaticae, as well as seven annonaceous acetogenins isolated from the seeds of the tropical tree Annona cherimolia (Family Annonaceae), were evaluated for their ability to inhibit or stimulate the production of biofilm by a strain of Pseudomonas aeruginosa. The tested compounds carry a gamma-lactone moiety in their structures. This structural feature is similar to the lactone moiety present in N-acyl homoserine lactones, compounds that play the important role of "quorum sensors" in the mechanisms of biofilm formation observed in many gram-negative bacteria. A special assay was employed to evaluate the influence of the tested plant compounds to inhibit or stimulate the production of biofilm in a P. aeruginosa wild strain. Most of the tested compounds affected the biofilm formation mechanism. Six sesquiterpene lactones isolated from Acanthospermum hispidum and one from Enydra anagallis as well as an acetogenin from Annona cherimolia strongly inhibited (69-77%) the biofilm formation when incorporated to a bacterial culture at a concentration of 2.5 microg/ml. However, one of the acetogenins, squamocin, stimulated the biofilm formation even at a concentration of 0.25 microg/ml. The study of substances affecting the biofilm formation can lead to the design of new strategies to control P. aeruginosa infections.