Effect of carvacrol on mature biofilms and bacterial quorum sensing

Abstract

The biofilm offers a protective environment for bacteria to grow in and survive under diverse conditions. This means that the bacteria will be protected against environmental factors such as pH changes, UV radiation and osmotic shock but as well against antimicrobial agents and the immunerespons of a host.1,8 Because of this protective layer of the biofilm it is very hard to remove them but possible anti-biofilm strategies are to prevent the bacteria to colonize a surface, the inhibition of signal molecules used for communication and breaking down the biofilm matrix.3,4 The communication process used by the bacteria in a biofilm is called quorum sensing and has shown to be necessary for mature biofilm formation, most biofilms will end at the first stages without quorum sensing.5,6 Using quorum sensing inhibitors might be making the biofilms more susceptible to antimicrobial treatments and the host immune system.22 A natural phytochemical with broad antimicrobial properties is carvacrol, a component of oregano, thyme and marjoram. It is used as a flavouring compound in for example, candy and baked goods.7 The aim of this project is to determine the effect of carvacrol on in vitro mature biofilms of Staphylococcus aureus, Salmonella enterica serovar Typhimurium and Pseudomonas aeruginosa. And to assess if carvacrol has a quorum sensing inhibitor activity, for which Chromobacterium violaceum will be used. The biofilms formed by Staphylococcus aureus showed a significant reduction after adding carvacrol of concentrations up to 4mM. For the in vitro biofilms of Salmonella enterica serovar Typhimurium and Pseudomonas aeruginosa there was no significant effect of carvacrol up to 8mM. Between concentrations of 0.2mM and 0.4mM carvacrol reduces the production of violacein, induced by quorum sensing, of Chromobacterium violaceum without a significant decrease of viable bacteria being present.