Effect of Tyrosol and Farnesol on Virulence and Antibiotic Resistance of Clinical Isolates of Pseudomonas aeruginosa

Abstract

Mixed-species biofilms could create a protected environment that allows for survival to external antimicrobials and allows different bacterial-fungal interactions. Pseudomonas aeruginosa-Candida albicans coexistence is an example for such mixed-species community. Numerous reports demonstrated how P. aeruginosa or its metabolites could influence the growth, morphogenesis, and virulence of C. albicans. In this study, we investigated how the C. albicans quorum sensing compounds, tyrosol and farnesol, might affect Egyptian clinical isolates of P. aeruginosa regarding growth, antibiotic sensitivity, and virulence. We could demonstrate that tyrosol possesses an antibacterial activity against P. aeruginosa (10 µM inhibited more than 50% of growth after 16 h cultivation). Moreover, we could show for the first time that tyrosol strongly inhibits the production of the virulence factors hemolysin and protease in P. aeruginosa, whereas farnesol inhibits, to lower extent, hemolysin production in this bacterial pathogen. Cumulatively, tyrosol is expected to strongly affect P. aeruginosa in mixed microbial biofilm.

Figure 1

Growth-inhibitory effects of farnesol on cells of P. aeruginosa (isolate 1). Cells were grown in MH broth medium containing farnesol at 0, 10, 50, 100, and 200 μM. Cell growth was expressed either as % growth after relating to the untreated cultures (at OD_600 nm) or as number of cells (CFU) counted after 24 h cultivation on MH agar. Error bars represent the standard deviation from three independent experiments.

Figure 2

Growth-inhibitory effects of tyrosol on cells of P. aeruginosa (isolate 1). Cells were grown in MH broth medium containing tyrosol at 0, 1.25, 2.5, 5, 10, 20, 40, and 80 μM. Cell growth was expressed either as % growth after relating to the untreated cultures (at OD_600 nm) or as number of cells (CFU) counted after 24 h cultivation on MH agar. Error bars represent the standard deviation from three independent experiments.