Molecular Evaluation of icaA Gene Transcription by Treatment with Rifampin and Garlic Extract in Staphylococcus aureus

Staphylococcus aureus is one of the pathogenic bacteria in humans that causes a wide range of diseases. Biofilm formation protects S. aureus against adverse environmental conditions and the host immune system. The genes that encode the most important biofilm constituents belong to the ica operon, one of the most important of which is the icaA gene. Rifampin is a broad-spectrum antibiotic, and garlic has beneficial antimicrobial effects due to its active ingredient allicin. In the present study, the antimicrobial effect of garlic extract at the phenotypic and molecular level and its effect on icaA biofilm gene expression and its comparison with rifampin were investigated.

A standard and two pathogenic strains of Staphylococcus aureus were evaluated. Antibiogram tests, minimum inhibitory concentration, and minimum bactericidal concentration were performed with rifampin antibiotic and garlic extract. A biofilm phenotypic test was performed with a 96-well microplate. After RNA extraction from the samples treated with rifampin and garlic extract, cDNA synthesis and then Real-time PCR were performed and the expression of icaA gene was measured.

The antibiogram test showed the antimicrobial effect of garlic extract on at least the standard strain and one of the pathogenic strains as compared to rifampin. The results of Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were determined for all three strains for rifampin and the combined combination of rifampin and garcin were 375 and 750 μg / ml, respectively. Real-time PCR results showed that in all studied strains, garlic extract and rifampin were able to reduce the expression of icaA gene and the combined use of these two substances led to a significant reduction in the expression of this gene. For the standard strain, rifampin and garlic extract reduced icaA expression to 88% and 60% in the control sample, respectively, and the combination of these two substances resulted in a reduction of icaA biofilm gene expression by about 50%.

In general, it can be concluded that rifampin antibiotic can be effective in inhibiting pathogenic bacteria such as Staphylococcus aureus. Garlic extract can also be used as an anti-bacterial drug at both phenotypic and molecular levels.