Antibiofilm Activity of Dracocephalum polychaetum Extract on Methicillin-Resistant Staphylococcus aureus

Antibiotic resistance among biofilm-producing pathogenic bacteria is a major health concern today. Plants, as a rich source of medicinal compounds, are interestingly explored for discovering new antibiotics.
In this study, the effect of Dracocephalum polychaetum Bornm extract on the growth, biofilm formation, and expression of biofilm-related genes in methicillin-resistant Staphylococcus aureus (MRSA) was explored.
Antimicrobial activity of D. polychaetum aerial part extract in MRSA samples was evaluated by agar well diffusion method. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the extract were determined according to the CLSI manual. Inhibition of biofilm formation was analyzed by microtitre plate method. Expression of icaA, icaD, bap, sar, and agr genes was studied by Reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) technique.
The antimicrobial effect of the extract against 20 MRSA strains was appropriate. The MIC and MBC of the extract were in the range of 0.781 - 25 mg mL-1 and 1.56 - 50 mg mL-1, respectively. Biofilm formation was inhibited in all of the isolated MRSA strains in sub-MIC concentrations. PCR results demonstrated that half of the samples had both icaA and icaD genes, about 1/3 had icaA gene, and 1/6 had merely icaD gene. RT-qPCR data showed that the expression of sar, bap, icaD and icaA genes was significantly reduced by the extract.
Collectively, the results demonstrated that D. polychaetum not only had anti-staphylococcus effects against MRSA but also suppressed biofilm formation both at phenotype and gene expression levels. Its effects are comparable to the effect of other Dracocephalum sp. Further in vivo studies can reveal the potential application of this plant against MRSA strains.