• cyclotides;
  • human and plant pathogenic bacteria;
  • Iranian Viola odorata;
  • new antimicrobial agents



Cyclotides are mini-proteins that are synthesized via the ribosomal pathway. They have a variety of biological activities such as antimicrobial, antitumour, anti-HIV activities. Because of their various bioactivities and unique stability, they are suitable candidate in drug design applications. The main aim of this study was to determine new antimicrobial agents, which can be used instead of chemical antibiotics. For this reason, we compared the antimicrobial effects of semipurified cyclotides against human and plant pathogenic bacteria.

Methods and Results

The cyclotides were isolated from the Iranian plant Viola odorata by fractionation methods and semipurified on a SPE-C18 column chromatography. Antimicrobial activities of extracted cyclotides were studied by radial diffusion assays (RDAs), minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). Data analysis showed that MIC of semipurified cyclotides was 1·6 mg ml−1 against Staphylococcus aureus, gram-positive bacteria. It was also revealed they are the most susceptible among human pathogenic bacteria used in this research. On the other hand, plant pathogenic bacteria are more susceptible than human pathogenic bacteria.


The results of the study show that cyclotides from Iranian V. odorata have potent antimicrobial activity against gram-negative, plant pathogenic bacteria.

Significance and Impact of the Study

This study is a part of our extended researches on finding new pharmaceutical potentials of plants and on developing new peptides for special purposes in a way that does not have harmful side effects or have the least side effects.