Treatment with paeoniflorin increases lifespan of Pseudomonas aeruginosa infected Caenorhabditis elegans by inhibiting bacterial accumulation in intestinal lumen and biofilm formation

Paeoniflorin is one of the important components in <i>Paeoniaceae</i> plants. In this study, we used <i>Caenorhabditis elegans</i> as a model host and <i>Pseudomonas aeruginosa</i> as a bacterial pathogen to investigate the possible role of paeoniflorin treatment against <i>P. aeruginosa</i> infection in the host and the underlying mechanisms. Posttreatment with 1.25-10 mg/L paeoniflorin could significantly increase the lifespan of <i>P. aeruginosa</i> infected nematodes. After the infection, the <i>P. aeruginosa</i> colony-forming unit (CFU) and <i>P. aeruginosa</i> accumulation in intestinal lumen were also obviously reduced by 1.25-10 mg/L paeoniflorin treatment. The beneficial effects of paeoniflorin treatment in increasing lifespan in <i>P. aeruginosa</i> infected nematodes and in reducing <i>P. aeruginosa</i> accumulation in intestinal lumen could be inhibited by RNAi of <i>pmk-1</i>, <i>egl-1</i>, and <i>bar-1</i>. In addition, paeoniflorin treatment suppressed the inhibition in expressions of <i>pmk-1</i>, <i>egl-1</i>, and <i>bar-1</i> caused by <i>P. aeruginosa</i> infection in nematodes, suggesting that paeoniflorin could increase lifespan of <i>P. aeruginosa</i> infected nematode by activating PMK-1, EGL-1, and BAR-1. Moreover, although treatment with 1.25-10 mg/L paeoniflorin did not show obvious anti-<i>P. aeruginosa</i> activity, the <i>P. aeruginosa</i> biofilm formation and expressions of related virulence genes (<i>pelA</i>, <i>pelB</i>, <i>phzA</i>, <i>lasB</i>, <i>lasR</i>, <i>rhlA</i>, and <i>rhlC</i>) were significantly inhibited by paeoniflorin treatment. Treatment with 1.25-10 mg/L paeoniflorin could further decrease the levels of related virulence factors of pyocyanin, elastase, and rhamnolipid. In addition, 2.5-10 mg/L paeoniflorin treatment could inhibit the swimming, swarming, and twitching motility of <i>P. aeruginosa</i>, and treatment with 2.5-10 mg/L paeoniflorin reduced the cyclic-di-GMP (c-di-GMP) level. Therefore, paeoniflorin treatment has the potential to extend lifespan of <i>P. aeruginosa</i> infected hosts by reducing bacterial accumulation in intestinal lumen and inhibiting bacterial biofilm formation.