Effect of salicylic acid on biofilm formation and on some virulence factors in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen resisting to several antibiotics. The resistance has been associated with bacterial biofilm formation favored by the presence of exopolysaccharides (EPS) and the ability to express many virulence factors. In our study, we investigated the use of salicylic acid (SA) to affect biofilm formation by use of crystal violet staining method (CVSM), swarming motility, pyocyanin and rhamnolipids production by P. aeruginosa ATCC 27853 and five clinical isolates of the same species. The results showed that MIC and MBC of SA against the studied bacteria were recorded around 10mM and 20mM respectively and the biofilm formation was highly decreased when incubated with the sub-inhibitory SA concentrations. Where we recorded an inhibition of 62,97% at the concentration of 4mM of SA for the reference strain P. aeruginosa ATCC 27853. Pyocyanin production and motility assay showed that sub-inhibitory concentrations of salicylic acid significantly decreased pyocyanin production and swarming motility, with relative swarming motility of 33% for P. aeruginosa ATCC 27853 at concentration of 4mM compared to non treated strain. Then the rhamnolipids production detected for only one isolate (P2) in the utilized medium PPGAS among the tested isolates was completely inhibited by 2mM or more of SA.