In vitro modulatory effects of lichen secondary metabolite vulpinic acid on pyoverdine production and quorum sensing-regulated traits in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a major opportunistic pathogen, especially involved with nosocomial infections. Siderophores such as pyoverdine are crucial for iron acquisition in bacteria and play an important role in virulence regulation. Therefore, targeting siderophore pathways has been suggested as a potential antivirulence approach. Lichens produce secondary metabolites with various effects, including the ability to influence quorum sensing (QS). In this study, lichen secondary metabolite vulpinic acid was investigated for its in vitro effects on pyoverdine production and specific QS-regulated traits of P. aeruginosa. Pyoverdine production, fluorescence quenching, QS-related virulence traits, and biofilm formation were evaluated using wild-type and GFP-expressing biosensor strains. In addition, quantitative qRT-PCR was performed to analyse QS and pyoverdine gene expressions. Results show that vulpinic acid application decreased pyoverdine production by 53.65% ± 5.45 and quenched the produced pyoverdine by 67.55% ± 2.98. The QS regulated genes lasB and rhlA were significantly downregulated. No biofilm inhibition at any applied concentration was observed, suggesting a selective influence on the bacteria rather than a global attenuation of virulence. These findings suggest that vulpinic acid can modulate specific virulence factors of P. aeruginosa in vitro, and provides a basis for further investigation of lichen secondary metabolites as antivirulence agents.