Introduction: Cationic antimicrobial peptides are produced by almost all organisms as part of a non-specific immediate defense barrier against infections [1, 2]. Antimicrobial peptides definition as less than 50 amino acid sequences, with positive charge and contain 50 % of hydrophobic amino acids. Antimicrobial peptides show broad-spectrum antimicrobial activities against various microorganisms [1, 3]. Although the potency of these antimicrobial peptides against susceptible pathogens is normally not as strong as conventional antibiotics, one of their major strengths is their ability to kill multi-drug-resistant bacteria at similar concentrations. Compared with conventional antibiotics, the killing of bacteria by peptides is extremely rapid and can involve multiple bacterial strains [4]. The buforins are histone-derived peptide belong to antimicrobial peptides. Buforin I is a 39 amino acid peptide that purified and characterized by Park et al. (1996) from the stomach of Asian toad which show strong antimicrobial [5]. Methods: The buforin I was purchased from Mimotopes company, Australia. Microorganisms used in this study included of Staphylococcus aureus ATCC 25923 and Staphylococcus aureus (MRSA) ATCC 33591 were procured from microbial collection, Ferdowsi University of Mashhad, Mashhad, Iran. Minimum inhibitory concentrations (MICs) was carried out using the micro broth dilution method. Serial dilutions (16, 14, 12, 10, 8, 6, 4, 2, 1 mg/mL) of the buforin I, and vancomycin in Mueller Hinton Broth (MHB) (Sigma-Aldrich) were prepared on a microtitre plate, and microbial suspensions were added to the microwells at 1/5 × 108 CFU/ml. The microtitre plates were then incubated at 37◦C for 24 h. Activity was recorded as red coloration in the wells after addition of Triphenyltetrazolium Chloride (concentration of 0.5 mg/mL). MICs were determined as the lowest concentrations that prevented visible growth. Results: Results showed that MICs of buforin I and vancomycin for Staphylococcus aureus were 10 and 10 µg/ml respectively. These values for Staphylococcus aureus (MRSA) were 14 and 12 µg/ml. Statistical comparisons (One way-ANOVA-LSD with p≤0.05) showed none significant difference between the MICs of buforin I and vancomycin for Staphylococcus aureus and Staphylococcus aureus (MRSA). Conclusion: Cationic antimicrobial peptides possess qualities that make them excellent candidates for antibacterial therapeutics, including a broad spectrum of antibacterial activity, ease of synthesis, and a novel mechanism of action. Low levels of peptide resistance are observed, and only after a large number of repeated passages in sub inhibitory concentrations. With the successful development of peptides and a sensible strategy for therapeutic implementation, we may remain one step ahead of antibiotic-resistant bacteria.

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