Treatment with paeoniflorin increases lifespan of infected by inhibiting bacterial accumulation in intestinal lumen and biofilm formation.

Paeoniflorin is one of the important components in plants. In this study, we used as a model host and as a bacterial pathogen to investigate the possible role of paeoniflorin treatment against infection in the host and the underlying mechanisms. Posttreatment with 1.25-10 mg/L paeoniflorin could significantly increase the lifespan of infected nematodes. After the infection, the colony-forming unit (CFU) and 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 infected nematodes and in reducing accumulation in intestinal lumen could be inhibited by RNAi of , , and . In addition, paeoniflorin treatment suppressed the inhibition in expressions of , , and caused by infection in nematodes, suggesting that paeoniflorin could increase lifespan of 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- activity, the biofilm formation and expressions of related virulence genes (, , , , , , and ) 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 , 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 infected hosts by reducing bacterial accumulation in intestinal lumen and inhibiting bacterial biofilm formation.