Antimicrobial activity of (KLAKLAK)–NH2 analogs against pathogenic microbial strains

[Display omitted] •The antimicrobial activity of a selection of (KLAKLAK)2-NH2 analogs has been determined.•New peptide Si16 shows a very well pronounced antagonistic activity against the used test pathogens, ranging from 45 to 67% of that of the corresponding positive controls.•the three long-chain peptides showed activity against both Gram-positive, Gram-negative bacterial test pathogens and yeasts;•The newly synthesized Si16 is a promising candidate for a medical drug due to its combined antibacterial and antiproliferative activities as well as its long hydrolytic stability. Many microorganisms pose a threat to human health due to the ever-increasing bacterial resistance to conventional drugs. Nowadays, searching for new alternatives to conventional antibiotics to fight bacterial resistance is a main task. Thus, natural molecules such as amino acids and peptides arise as possible solutions to the problem. The antimicrobial activity of targeted compounds was studied by the agar-diffusion method, using the prepared working solutions of the targeted peptides with the corresponding concentrations. The results of the antimicrobial activity against different test pathogens show specificity, as antimicrobial activity against the used test microorganisms was not found in the investigated short-chain synthetic peptides Si6, Si3 and Si13. Antimicrobial activity against Bacillus cereus, Staphylococcus aureus, Staphylococcus epidermidis, Propionibacterium acnes, Escherichia coli, Pseudomonas aeruginosa, and the yeasts Malassezia furfur and Candida albicans was established for the long-chain synthetic peptides Si1, Si5 and Si16, except Si5 which does not show activity against pathogenic fungal strain C. albicans. The compound Si16 where natural Leu in (KLAKLAK)2-NH2 is replaced by unnatural Nle is the best candidate for medical drug due to the combined antibacterial and antiproliferative effect as well as long hydrolytic stability.