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Abstract
Pseudomonas aeruginosa, a commonly found, nosocomial, opportunistic pathogen, is characterized by its ability to form biofilm to protect itself from various external pressures. Infection by this species is especially prominent in cystic fibrosis patients and is difficult to treat, especially with the rampant increase in antibiotic resistance. Salicylic acid has been indicated in biofilm attenuation of P. aeruginosa while quorum sensing plays a key role in the growth and maintenance of a biofilm. Many virulence factors in biofilm formation are also involved in motility. Here, we investigated the use of salicylic acid in biofilm and swarming motility attenuation through the quorum sensing gene, lasR. Overnight cultures of wildtype P. aeruginosa and a lasR deficient mutant were incubated with varying concentrations of salicylic acid. Their biofilm densities were assessed by crystal violet assay. An inversely proportional relationship between salicylic acid and biofilm density was found for both strains with a maximum inhibitory concentration of ~2 mM. Differences in biofilm density between strains were statistically significant (p<0.05) for salicylic acid concentrations above 0.25 mM, but not in the expected manner. Swarming capabilities of both strains were assessed using LB growth plates with varying concentrations of salicylic acid. Conclusive results were not obtained due to the drastic differences among replicates, but results indicate swarming motility to be independent of salicylic acid and the quorum sensing gene, lasR. In conclusion, salicylic acid inhibits biofilm formation in a concentration dependent manner through mechanisms other than the lasR quorum sensing gene.