Eradication of vancomycin-resistant Staphylococcus aureus on a mouse model of third-degree burn infection by melittin: An antimicrobial peptide from bee venom.

Third-degree burn infections caused by antibiotic-resistant bacteria are of high clinical concern. Chemical antibiotics are not promising in eradication of bacterial infections. In this challenging condition, antimicrobial peptides (AMPs) are recently introduced as novel promising agents to overcome the issue. Accordingly, our study aimed to evaluate the efficiency of 'melittin' as natural peptide in bee venom, in eradicating vancomycin resistant Staphylococcus aureus (VRSA) on a mouse model of third-degree burn infection. In vitro pharmacological value of melittin was determined by examining its inhibitory and killing activities on VRSA isolates at different doses and time periods. The action mechanism of 'melittin' was evaluated by fluorescent release assay and Field Emission Scanning Electron Microscopy (FE-SEM) analyses. In vivo activity and toxicity of melittin were also examined on a mouse model of third-degree burn infection. The Minimum Inhibitory Concentration (MIC) and the Minimum Bactericidal Concentration (MBC) of melittin on all isolates ranged from '0.125-2 µg/mL' and '0.125-4 µg/mL', respectively. Rapid antibacterial activity of melittin on VRSA isolates was demonstrated by killing kinetics assays. Fluorometric and FE-SEM analyses indicated the membranolytic effects of melittin on VRSA isolates. The colonized VRSA bacteria were eradicated by melittin at 16 µg, in a single dose. No dermal toxicity and in vivo hemolysis were observed in the examined mice. The lack of in vivo toxicity of melittin along with its potent antibacterial activity indicated its promising therapeutic value as a topical drug against S. aureus associated third-degree burn infections.

Single dose eradication of extensively drug resistant Acinetobacter spp. In a mouse model of burn infection by melittin antimicrobial peptide.

Bacterial infections caused by antibiotic resistant bacteria are the leading cause of morbidity and mortality after burn injuries. This issue has driven the need for promising antimicrobial drugs to eradication of bacterial pathogens. Accordingly, we aimed to determine the therapeutic value of melittin, as a natural Antimicrobial peptide (AMP), in eradication of extensively drug-resistant (XDR) Acinetobacter spp. on a mouse model of third degree burn infection. Melittin killed all examined XDR isolates at 4 µg/mL up to 3 h. Melittin caused significant fluorescence release from XDR isolates at the minimum dose of 0.062 µg/mL. Vesicle formation on the membrane and squeezing of bacteria followed by cell lysis indicated the membranolytic effect of melittin. Melittin at 32 µg/mL completely eradicated the colonized XDR bacteria on infected burn mice during 2 h. No toxicity was observed on injured or healthy derma, as well as circulating Red Blood Cells (RBCs) in the examined mice. Potent promising antibacterial activity of melittin and the lack of toxicity at the therapeutic dose can clarify that melittin can be implemented as a topical drug lead in a preclinical trial of third degree burn infections.

Highly Synergistic Effects of Melittin with Conventional Antibiotics Against Multidrug-Resistant Isolates of Acinetobacter baumannii and Pseudomonas aeruginosa.

BACKGROUND: Morbidity and mortality due to multidrug-resistant (MDR) bacteria are of great concern in burn patients. In this critical condition, synergism between antimicrobial peptides and conventional antibiotics would be a promising strategy. Accordingly, this study aimed to determine the therapeutic value of melittin as a natural peptide by examining its synergistic effect with conventional antibiotics against MDR isolates of Acinetobacter baumannii and Pseudomonas aeruginosa. MATERIALS AND METHODS: Fifteen clinical isolates for each kind of bacteria were collected from burn patients. Antibiotic susceptibility of all isolates was evaluated by disk diffusion method. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration for melittin, colistin, doripenem, doxycycline, and ceftazidime were also examined. Fractional inhibitory concentration (FIC) of melittin in combination with the antibiotics was determined for six MDR isolates. The cytotoxicity of melittin in combination with the antibiotics was examined on a normal human cell line. RESULTS: The geometric means of MIC (GMMIC) for melittin and doripenem after combination were reduced to 61.5- and 51.5-fold, respectively, against MDR A. baumannii isolates. These reductions for melittin-doripenem and melittin-ceftazidime against MDR P. aeruginosa isolates were (63.5 and 58)-fold and (16 and 11)-fold, respectively. FIC for melittin-doripenem against A. baumannii and FIC for melittin-doripenem and melittin-ceftazidime against P. aeruginosa strains were ≤0.5. This issue caused a decrease of up to 104-, 68-, and 17-fold, respectively, in the cytotoxicity of melittin. CONCLUSION: In conclusion, the synergism of melittin at its nontoxic dose with doripenem and ceftazidime could be of great therapeutic value as a topical drug against burn infections caused by MDR bacteria.