The role of quorum sensing (QS) in the regulation of virulence factor production in Pseudomonas aeruginosa is well established. Increased antibiotic resistance in this bacterium has led to the search for new treatment options, and inhibition of the QS system has been explored for potential therapeutic benefits. If the use of QS inhibitory agents were to lead to a reduction in bacterial virulence, new approaches in the treatment of P. aeruginosa infections could be further developed. Accordingly, we examined whether human serum paraoxonase 1 (hPON1), which uses lactonase activity to hydrolyse N-acyl homoserine lactones, could cleave P. aeruginosa-derived signalling molecules. hPON1 was purified using ammonium sulfate precipitation and hydrophobic interaction chromatography (Sepharose 4B-L-tyrosine-1-naphthylamine). Different concentrations of hPON1 were found to reduce various virulence factors including pyocyanin, rhamnolipid, elastase, staphylolytic LasA protease and alkaline protease. Although treatment with 0.1-10 mg hPON1 ml 21 did not show a highly inhibitory effect on elastase and staphylolytic LasA protease production, it resulted in good inhibitory effects on alkaline protease production at concentrations as low as 0.1 mg ml 21. hPON1 also reduced the production of pyocyanin and rhamnolipid at a concentration of 1.25 mg ml 21(within a range of 0.312-5 mg ml 21). In addition, rhamnolipid, an effective biosurfactant reported to stimulate the biodegradation of hydrocarbons, was able to degrade oil only in the absence of hPON1. INTRODUCTIONQuorum sensing (QS) is a process of bacterial communication used to collectively control group behaviours (Ng & Bassler, 2009;Rutherford & Bassler, 2012). Pseudomonas aeruginosa perceives its local population density using a QS system: as the concentration of the signalling molecules passes a given threshold, the bacteria regulate production of certain virulence factors. To orchestrate the synchronous production of virulence factors, P. aeruginosa relies on two major LuxI/R QS systems: the Las and Rhl systems (Pesci et al., 1997;Schuster et al., 2003). The LuxI homologues LasI and RhlI are responsible for synthesis of the Las and Rhl signals, N-(3-oxododecanoyl)-L-homoserine lactone (PAI1) and N-butanoyl-L-homoserine lactone (PAI2), respectively. PAI1 activates the LuxR-type transcription factor LasR, and, in turn, LasR-PAI1 induces the production of LasB elastase, LasA protease, alkaline protease and LasRI (Gambello et al., , 1993Seed et al., 1995). PAI2 cooperates with the cognate regulator RhlR to enhance the production of rhamnolipid, pyocyanin and LasB elastase (Latifi et al., 1995;Pearson et al., 1995). Expression of many of the virulence factors in P. aeruginosa is controlled by the QS system (Venturi, 2006). Different strains of P. aeruginosa secrete several extracellular proteolytic enzymes that have been implicated as virulence factors. These enzymes include protease IV, alkaline protease, and LasA and LasB elastases (Caballero et al., 2001). These proteases pr...

Human serum paraoxonase 1 (PON1; EC 3.1.8.1) is a high-density lipoprotein associated, calcium-dependent enzyme that hydrolyses aromatic esters, organophosphates and lactones and can protect the low-density lipoprotein against oxidation. In this study, in vitro inhibition effect of some dihydroxy coumarin compounds namely 6,7-dihydroxy-3-(2-methylphenyl)-2H-chromen-2-one (A), 6,7-dihydroxy-3-(3-methylphenyl)-2H-chromen-2-one (B) and 6,7-dihydroxy-3-(4-methylphenyl)-2H-chromen-2-one (C) on purified PON1 were investigated by using paraoxon as a substrate. PON1 was purified using two-step procedures, namely ammonium sulphate precipitation and Sepharose-4B-L-tyrosine-1-naphthylamine hydrophobic interaction chromatography. The purified enzyme had a specific activity of 11.76 U/mg. The dihydroxy coumarin derivatives of A and B compounds inhibited PON1 enzyme activity in a noncompetitive inhibition manner with K(i) of 0.0080±0.256 and 0.0003±0.018 mM values, respectively. C compound exerted an uncompetitive inhibition of PON1 enzyme activity with K(i) of 0.0010±0.173 mM. Moreover, dihydroxy coumarin derivatives of A, B and C compounds were effective inhibitors on purified human serum PON1 activity with IC(50) of 0.012, 0.022 and 0.003 mM values, respectively. IC(50) value of unsubstituted 6,7 dihydroxy coumarin was found as 0.178 mM. The present study has demonstrated that PON1 activity is very highly sensitive to studied coumarin derivatives.

Psychotropic drugs are known to have antimicrobial activity against several groups of microorganisms. The antidepressant agents such as duloxetine, paroxetine, hydroxyzine and venlafaxine are shown to act as efflux pump inhibitors in bacterial cells. In order to the investigation of the effects of psychotropic drugs were determined for clinically significant pathogens by using standart broth microdillusion method. The anti-quorum sensing (anti-QS) activity of psychotropic drugs was tested against four test pathogens using the agar well diffusion method. All drugs showed strong inhibitory effect on the growth of S. typhimurium. Additionally, quorum sensing-regulated behaviors of Pseudomonas aeruginosa, including swarming, swimming and twitching motility and alkaline protease production were investigated. Most effective drugs on swarming, swimming and twitching motility and alkaline protease production, respectively, were paroxetine and duloxetine; duloxetine; hydroxyzine and venlafaxine; paroxetine and venlafaxine; venlafaxine. Accordingly, psychotropic drugs were shown strongly anti-QS activity by acting as bacterial efflux pump inhibitors and effection on motility and alkaline protease production of P. aeruginosa.

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Objectives: In the present study, it was reported the effects of some nutritional (amino acid, carbon, nitrogen and metal sources) and physical factors (pH and temperature) on antibacterial substance activity of Brevibacillus laterosporus EA62. Methods: The agar well diffusion assay was performed to evaluate the antibacterial activity of the substance. The antibacterial activity of the new substance was examined against four pathogenic bacteria under different nutritional and physical conditions. Results: The best antibacterial activity was obtained in modified medium consists of the 5% glucose, 0.1% tryptone, 0.05% MgSO4 + CaCO3 and 0.5% glutamic acid. For physical parameters, maximal activity was observed after 72 h when incubated at 37°C, pH 7.0. Conclusions: This study indicates that Brevibacillus laterosporus EA62 could be an important source of antibacterial substances under this medium optimization.

The ethyl acetate and methanol extracts of Phlomis pungens var. pungens, P. nissolii, P. armeniaca and Stachys byzantina, S. cretica L. subsp. mersiaea and S. cretica L. subsp. Smyrnaea were evaluated for their antibacterial and antibiofilm activities. Five bacterial species were used are Bacillus subtilis, Pseudomonas aeruginosa, Shigella sonnei, Salmonella typhimurium and Yersinia enterocolitica. The ethyl acetate and methanol extracts of plant species showed good antibacterial activity against all bacterial strains. More significantly, ethylacetate and methanol extracts of all Phlomis species were found to be more effective on degredation of mature biofilm against all used bacterial strains than extracts of Stachys species. The findings of the present study highlight the promising role of Phlomis and Stachys extracts as new lead structures in the search for novel antibacterial and antibiofilm agents.