Molecular study of icaD biofilm gene expression by plant extracts of Mary thistle and ginseng in Staphylococcus aureus

The biofilms production by Staphylococcus aureus is one of the problematic factors of these bacteria.One of the biofilm gene loci is icaD, which plays an important role in biofilm production. Many plants have medicinal and antimicrobial properties. In this study the antimicrobial properties and molecular effects of Mary thistle and ginseng extracts on the expression of icaD biofilm gene in S. aureus were studied. The extracts of Mary thistle and ginseng were prepared and after evaluation of bacterial growth inhibition zone under the influence of these extracts, the inhibitory effect of growth was assessed by MIC test. Following RNA extraction and cDNA synthesis from strains treated with Mary thistle and ginseng extracts and untreated strains, the expression levels of icaD biofilm gene in pathogen and standard strains of S. aureus were analyzed by Real time PCR. The diameter of growth inhibition zone in standard strain affected by 100 mg/ml of the Mary thistle and ginseng extracts were 10 and 8 mm, respectively. The diameter of the growth inhibition zone for the pathogen strain was 10 and 12 mm, respectively. A combination of equal use of Mary thistle and ginseng extracts also created a 15 mm growth inhibition zone in both studied strains. In different concentrations of plant extracts (39.6 g/ml to 5000 g/ml) used in MIC, all strains were grown. According to Real time PCR results, icaD biofilm gene expression increased 17-fold in the standard strain treatment with Mary thistle extract and 24-fold under the influence of ginseng extract. In the pathogenic strains, icaD gene expression was reduced to 0.3% under the influence of Mary thistle extract and the expression of this gene was almost inhibited. Ginseng extract also reduced the expression of this gene in the pathogen strain to about 49%. The combined use of Mary thistle and ginseng extracts also reduced icaD gene expression in the pathogen strain to about 6% of the control sample and led to a 94% reduction in the expression of this gene.