Effect and Mechanism of Andrographolide on the Recovery of Pseudomonas aeruginosa Susceptibility to Several Antibiotics

Effectiveness and mechanism of action of andrographolide on the recovery of Pseudomonas aeruginosa susceptibility to antibiotics was investigated. In the presence of andrographolide, the Mueller-Hinton broth dilution method measured minimal inhibitory concentrations (MIC) of ceftazidine, cefpirome, chloramphenicol, L-ofloxacin, kanamycin, imipenem and meropenem. Real-time fluorescence quantitative polymerase chain reaction was used to determine mexB mRNA expressions in P. aeruginosa PAO1 strain and MexAB-OprM overexpressing strain. Relative mexB mRNA expression was detected in both strains incubated for 3 and 9 h. When andrographolide-treated groups were compared with controls, the MIC of ceftazidine, cefpirome, L-ofloxacin and meropenem for both strains decreased, and the relative mexB mRNA expression was significantly lower, although between andrographolide groups there were no significant differences. Compared with the inactivated quorum-sensing system, relative amounts of mexB mRNA in the PAO1 strain and MexAB-OprM overexpressing strain in the activated quorum-sensing system increased 10- and 30-fold, respectively. Andrographolide recovered P. aeruginosa susceptibility to antibiotics and reduced the MexAB-OprM efflux pump expression level.