Inhibitory Effect of Glycyrrhizin on Biofilm Formation of Pseudomonas aeruginosa
HUANG Pan1, WANG Zhi-Peng2, XIAO Chen-Wen2, JI Quan-An2, BAO Guo-Lian1,2,*, LIU Yan2,*
1 College of Chemistry and Life Science, Zhejiang Normal University, Jinhua 321004, China; 2 Institute of Animal Husbandry and Veterinary Medicine, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China
Abstract：Pseudomonas aeruginosa has multiple drug resistance, and the formation of biofilm is one of its important drug resistance mechanisms. Glycyrrhizin (GLY) has antibacterial effect. In order to investigate the effects of antibacterial activity and biofilm formation of GLY on clinical isolates of multidrug resistant P. aeruginosa, G1 strain (GenBank No. MZ683158) and G2 strain (GenBank No. MZ683159) were isolated from the eye secretions of rabbits suffering from keratitis (Zhejiang Shengzhou wool rabbit 'White King', Leporidae angora). Further, the minimum inhibitory concentration (MIC) of GLY on G1 and G2 strains was determined by microdilution method, crystal violet staining was used to quantify biofilm, the effect of GLY on biofilm morphology was observed by scanning electron microscope (SEM), and the expression of pelA, algA, rhlI, rhlR and pslA was analyzed by qPCR. The results showed that MICs of GLY against G1 and G2 strain were 40 and 20 mg/mL, respectively; both G1 and G2 strains could form biofilm, and G1 strain had stronger ability. The biofilm formation of G1 and G2 strains decreased significantly with the treatment of 20 mg/mL GLY (P<0.01). SEM observation showed that 5 mg/mL GLY significantly reduced the biofilm formation; under the treatment of 10 mg/mL GLY, the bacteria were dispersed and no obvious biofilm structure was found. The expression of pelA increased after 5 mg/mL GLY treatment without signifcant difference, while those of algA, rhlI, pslA and rhlR were significantly decreased (P<0.01). After 10 mg/mL GLY treatment, the relative expression of pelA, algA, rhlI, rhlR and pslA were significantly decreased (P<0.01) compared with the control. In conclusion, GLY had a inhibitory regulatory effect on the synthesis of P. aeruginosa biofilm in a dose-dependent manner, which might be due to the down regulating of related genes. This study provides a reference for in-depth study of the effect of GLY on P. aeruginosa biofilm and the treatment of P. aeruginosa keratitis in rabbits.
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