Anti-Quorum Sensing and Anti-Biofilm Activity of Pelargonium × hortorum Root Extract against Pseudomonas aeruginosa: Combinatorial Effect of Catechin and Gallic Acid

Abstract

HPLC-UV was used to compare the major constituents of two <i>Pelargonium × hortorum</i> cultivars and <i>Pelargonium sidoides</i> root extract. It revealed the presence of catechin and gallic acid in high concentrations and the absence of umckalin in <i>P. × hortorum</i> root extracts. The antibacterial activity of these extracts was screened against 19 <i>Pseudomonas aeruginosa</i> clinical isolates. <i>P. × hortorum</i> root extracts showed the lowest MIC values (512-1024 µg/mL). This activity was concluded to be attributable to the high concentrations of catechin and gallic acid. The anti-biofilm activity of catechin, gallic acid, and their combination was examined by a crystal violet assay. The combination reduced the percentage of strong and moderate biofilm-forming isolates from 52.63% to 5.26%. The impact on <i>las</i>I and <i>las</i>R genes expression using qRT-PCR and simultaneous docking against <i>Las</i>R protein was explored. The combination downregulated <i>las</i>I and <i>las</i>R gene expression in eight and six <i>P. aeruginosa</i> isolates, respectively, and showed the greatest docking score. Additionally, the in vivo protection capability of this combination in infected mice showed enhancement in the survival rate. Our study revealed the potential biofilm and quorum-sensing-inhibitory activity of the catechin and gallic acid combination as a novel alternative to inhibit bacterial pathogenicity.