Laurel extracts inhibit Quorum sensing, virulence factors and biofilm of foodborne pathogens

Antimicrobial, antibiofilm, anti-Quorum sensing (QS) and virulence factors inhibitory capacity of different polarity Laurus nobilis extracts against several pathogenic microorganisms were studied. Some extracts exhibited antibiotic effect against Staphylococcus aureus multidrug-resistant strains. However, all extracts (100 mu g/mL) inhibited to some extent the biofilm of most bacteria tested (until 40% for Gram-negative and 76% for Grampositive). Hexane (HE) and chloroform extract (CE) were potent inhibitors of S. aureus biofilm and the microscopies further confirmed an important reduction in adherent cells. Polystyrene surfaces coated with these extracts showed a decrease in bacterial adhesion with the resulting inhibition of S. aureus biofilm formation and biofilm activity. Moreover, they also interfere with the coagulase and hemolysin activities of this bacterium. With respect to Gram-negative bacteria, these extracts showed anti-QS activity against Chromobacterium violaceum and inhibited biofilm formation, swarming motility, pyocyanin production, and elastase activity of Pseudomonas aeruginosa. Chemical analysis of HE and CE revealed that the fatty acids were the main compounds, particularly linolenic, oleic and hexadecanoic acids followed by the oxygenated monoterpenes. Non-toxic laurel extracts offer a natural alternative to control contamination and/or spoilage of food, as well as infectious diseases, by attacking the biofilm and the virulence of Gram-positive and Gram-negative bacteria.