The effect of different doses of silymarin, extracted from the seeds of the Silybum marianum L. Gaertn on the growth of 6 bacterial species

Uncontrolled use of chemical drugs increases microbial strains resistant to antibiotics. There is an urgent need for discovery of new anti microbial compounds. Nowadays, many researchers have been done to introduce antibacterial compounds with natural origin. Aim of this study was in vitro assessment of antimicrobial effects of methanolic extract from dried fruits of Silybum marianum. Hungarian seeds of Silybum marianum were defatted by ethyl acetate. The flavonolignans were extracted with methanol. Antimicrobial effects of methanolic extract (pure extract, 2000, 1000, 500, 250 125, 62.5 and 0 mg/ml) were examined on six species of microorganisms (Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa, Escherichia coli, Bacillus cereus, Bacillus antheracis) with three methods such as disk diffusion, well diffusion, porpelite and spread-plate methods. The experiment was performed three times with three replicates. According to results of this investigation, there was no growth inhibition zone in disk diffusion method for all dilutions of plant extract. The highest growth inhibition zone (19 mm) was observed in Strep. pyogenes in well diffusion method. In porpelite method, the growth inhibition zone was indicated in all of dilutions plant extract for B. cereus culture, in 2000 and 1000 mg/ml for B. antheracis and in 2000 mg/ml for Strep. pyogenes. Our results showed that, the extract had antibacterial effect on B. Cereus, B. anthracis and Strep. pyogenes in spread-plate method but had less effect on S. aureus, P. aeruginosa and E. coli. With attention to our finding, it could be concluded that methanolic extract of Silybum marianum has antibacterial effects on current clinical pathogen microorganisms. Therefore, it must be evaluated in vivo and clinically.