The term "cyclotide" was coined in year 1999, despite the basic studies in the field dateback to the early 1970s. The distinguishing features of cyclotides are their molecularstructure: generally, app. 28-37 amino acids and cyclized peptide backbone together withthe three disulfide bonds in knotted conformation. Cyclotides were discovered in plantspecies belonging to six plant families including Violaceae (violet). They're interestingfor medicine because of their wide range of activities (Anti-HIV, insecticidal, and anti-microbial) as well as the stability of their molecular scaffold. Many of the activities wereattributed to the cyclotide ability to disrupt biological membranes. The present studyfocused on extraction and isolation of the cycloviolacin O2 (cyO2) cyclotide from theplant Viola odorata. Plant material was extracted in several steps. The peptide waspurified using different liquid chromatography techniques like flash liquidchromatography (FLC), high performance liquid chromatography (HPLC) guided bymass spectrometry. Secondly, the project investigated the involvement of the gram-negative bacterium S. enterica biological membrane composition in mechanism ofbacteria resistance against cyclotides. Previously developed cyO2-resistant bacteriamutants were obtained from a microbiologic archive. Bacteria were regrown in a freshliquid media and extracted. Their membrane lipid composition was analyzed with LC-MS and compared. The extraction procedure yielded 1,4 mg of pure cyO2 peptide. Thepurity was confirmed with UV-HPLC and LC-MS. The qualitative lipid profiles weresimilar among the resistant mutants and wild type bacteria. However, due to technicalreasons, the quality of the results did not enable to compare the quantities of the differentlipids among the samples and the quantitative differences may be more important inresistance against cyclotides