Figure 7. Effect of pure compounds on QS-regulated traits of P. aeruginosa.

Bacterial growth was measured as OD ₇₆₄; OD of pyoverdine was measured at 405 nm, and Pyoverdine Unit was calculated as the ratio OD ₄₀₅/OD ₇₆₄ (an indication of pyoverdine production per unit of growth), Pyocyanin Unit was calculated as the ratio OD ₅₂₀/OD ₇₆₄ (an indication of pyocyanin production per unit of growth). ‘Control’ in this figure is the vehicle control (0.5%v/v DMSO), which did not exert any effect on growth and pigment production of P. aeruginosa. ( A) Effect of cinnamic acid on growth and QS-regulated pigment production in P. aeruginosa. ( B) Effect of chlorogenic acid on growth and QS-regulated pigment production in P. aeruginosa. ( C) Effect of catechin on growth and QS-regulated pigment production in P. aeruginosa. ( D) Cinnamic acid and chlorogenic acid act as signal-supply inhibitors against P. aeruginosa, whereas catechin acts as a signal-response inhibitor. ( E) P. aeruginosa receiving pre-incubation with cinnamic acid or chlorogenic acid becomes more susceptible to cephalexin. ( F) Pre-treatment of P. aeruginosa with cinnamic acid or chlorogenic acid reduces its virulence towards C. elegans: Catechin (50 μg/ml) and gentamicin (0.1 μg/ml) employed as positive controls conferred 100% and 80% protection on worm population respectively; DMSO present in the ‘vehicle control’ at 0.5%v/v did not affect virulence of the bacterium towards C. elegans; DMSO (0.5%v/v) and compounds at tested concentrations showed no toxicity towards the worm. * p<0.05, ** p<0.01, *** p<0.001; AS, Antibiotic susceptibility; QS, Quorum sensing.