Inhibition of Pseudomonas aeruginosa by herbal medicines

Background: Pseudomonas aeruginosa is a ubiquitous bacterium frequently associated with nosocomial infections. It has acquired resistance against various antibiotics and has become a serious threat to human health, especially in hospital environments. In order to develop a new treatment for P. aeruginosa infections, we examined the effect of herbal medicines (HM) on P. aeruginosa motility and protease production. Methods and materials: The effects of 34 types of HM on the standard P. aeruginosa strain PAO1 and multidrug resistant P. aeruginosa (MDRP) were examined. Extraction of HM The HMs were dissolved in 1% dimethylsulfoxide, shaken overnight, and then centrifuged. The supernatants were used as HM extracts. Motility test Media containing 9 ml agar and 1 ml HM extract were prepared. Ten microliters of the adjusted bacterial solution was added dropwise to each medium, and the diameter of bacterial spread was measured. Protease production test Each HM extract was mixed with an equal volume of LB broth. To these mixtures, 10 μl of 0.5 McFarland standard bacterial solution was added, and the solutions were incubated for 24 hours. Ten microliters of the bacterial solutions were then added to LB agar containing 1.5% skimmed milk. A concentration gradient was created at each HM. After 24 hours, the presence or absence of a clearance zone was determined. Results: Motility: Five HMs exhibited inhibitory effects against P. aeruginosa. Zanthoxylum piperitum (ZP) affected motility the most. Swarming- ZP reduced liquid surface motility of by 50% for PAO1 and 70% for MDRP. Swimming- ZP decreased the swimming ability by 50% for PAO1 and 77% for MDRP. Twitching- ZP decreased solid surface motility by 74% for PAO1 and 83% for MDRP. Protease: Protease production was inhibited by ≥1.25 mg/dl ZP and suppressed by ≥2.5 mg/dl Coptis japonica and Ephedra. Conclusion: The high inhibitory effect on motility of P. aeruginosa may indirectly inhibit biofilm formation. Moreover, the inhibition of protease production by P. aeruginosa may suppress its pathogenicity.