E!ects of Allicin on the Formation of Pseudomonas aeruginosa Biofilm and the Production of Quorum-Sensing Controlled Virulence Factors

"e Gram-negative Pseudomonas aeruginosa bacterial pathogen is reputed for its resistance to multiple antibiotics, and this property is strongly associated with the development of biofilms. Bacterial biofilms form by aggregation of microorganisms on a solid surface and secretion of an extracellular polysaccharide substances that acts as a physical protection barrier for the encased bacteria. In addition, the P. aeruginosa quorum-sensing system contributes to antibiotic resistance by regulating the expression of several virulence factors, including exotoxin A, elastase, pyoverdin and rhamnolipid. "e organosulfur compound allicin, derived from garlic, has been shown to inhibit both surface-adherence of bacteria and production of virulence factors. In this study, the e!ects of allicin on P. aeruginosa biofilm formation and the production of quorum-sensing controlled virulence factors were investigated. "e results demonstrated that allicin could inhibit early bacterial adhesion, reduce EPS secretion, and down-regulate virulence factors’ production. Collectively, these findings suggest the potential of allicin as a therapeutic agent for controlling P. aeruginosa biofilm. K e y w o r d s: Pseudomonas aeruginosa, allicin; antibiotic resistance, biofilm, virulence factor Lin Lihua and Wang Jianhui et al. 3 244 "e organosulfur compound allicin which is derived from garlic, has antibacterial properties, and has been reported to e!ectively inhibit Staphylococcus epidermis, another common nosocomial pathogen (PérezGiraldo et al., 2003) and Aggregatibacter actinomycetemcomitans, the key etiologic agent of the severe form of localized aggressive periodontitis (Velliyagounder et al., 2012). At concentrations below the minimum inhibitory concentration (MIC), allicin has been shown to prevent adherence of S. epidermis to polystyrene microtiter plates (Pérez-Giraldo et al., 2003), suggesting a potential therapeutic role for allicin as a biofilm inhibitor. A previous study of allicin’s e!ects on P. aeruginosa determined that this agent can specifically inhibit QS-related gene expression (Bjarnsholt et al., 2005). "is finding led to the hypothesis that allicin may act as an anti-biofilm agent against P. aeruginosa. "erefore, this study was designed to investigate the e!ects of allicin on P. aeruginosa biofilm formation, including the secretion of extracellular polysaccharide substances (EPS) and induced expression of QS-mediated virulent factors.