d-Leucine Modified CM11 Peptide has Admissible Antibacterial Activity with Low Cytotoxic Properties Against Vero Cell Line

Discovering novel antimicrobials is highly crucial to combat drug-resistant bacteria. Antimicrobial peptides (AMPs) are one of the compounds that are being studied as suitable candidates for antibiotics. Therefore, the aim of the present study was to investigate the antibacterial and cytotoxic properties of the d -leucine modified CM11 peptide. To assess the antibacterial activity, minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC) and bactericidal killing assay were utilized against multidrug-resistant (MDR)clinical isolates and standard strains of methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli , Pseudomonas aeruginosa and Salmonella enterica serovartyphi. In addition, the scanning electron microscope (SEM) was used to evaluate the effect of the peptide on the bacterial cell structure and morphology. Also, MTT assay was used to determine the cytotoxicity potential of the d -leucine modified CM11 peptide on the Vero cell line. d -leucine modified CM11 exhibited good bactericidal properties and the MIC and MBC values were ranged from 4 to 32 and 8–64 µg ml −1 , respectively. The effect of the d -leucine modified CM11 peptide on the morphology and bacterial structures was confirmed by the SEM. The IC50 value of the d -leucine modified CM11 peptide against Vero cells was 160 µl.ml −1 .Also, there was no significant difference between the toxicity of the d -leucine modified CM11 peptide with the original CM11 peptide (p > 0.05).Antibacterial and non-toxicity of the d -leucine modified CM11 peptide, which is reported for the first time in this study, speculate the use of this peptide as safe antibacterial agent.