Evaluation of three plant extracts against biofilm formation and expression of quorum sensing regulated virulence factors in Pseudomonas aeruginosa.

Following the increasing antibiotic resistance of pathogenic bacteria, the use of medicinal herbs as antibacterial agents has attracted growing attention. Pseudomonas aeruginosa is a human opportunistic pathogen that uses quorum sensing for regulating virulence gene expression (pyocyanin, protease, and elastase production and biofilm formation). This study examined the anti-quorum sensing activity of Quercus infectoria, Zataria multiflora and Trachyspermum copticum extracts on standard P. aeruginosa strain. The minimum inhibitory concentration (MIC) of Q. infectoria, Z. multiflora and T. copticum extracts for standard P. aeruginosa strain was determined through micro dilution. Microtiter plates were used to evaluate the anti-quorum sensing effects of the three extracts (at a sub-MIC concentration) on pyocyanin, protease, and elastase production and biofilm formation. The acetone extract of Q. infectoria showed the highest anti-quorum sensing activity and reduced the pyocyanin, protease, and elastase production and biofilm formation by 89.1%, 78%, 73.3%, and 70.1%, respectively. The corresponding values were 88.2%, 72.1%, 69%, and 61.1% for the methanol extract of Z. multiflora and 70.6%, 63.42%, 60.1%, and 59.1% for the methanol extract of T. copticum. Considering the high anti-quorum sensing activity of the studied extracts, especially the acetone extract of Q. infectoria, these herbs can be used as antipathogenic drugs.