Synergistic Effect of Frog Skin Antimicrobial Peptides in Combination with Antibiotics Against Multi host Gram-Negative Pathogens

Abstract

In the present study, two brevinin-1 peptides (Brevinin1 HYba1 and 2; B1 and B2 for ease) identified from the skin secretion of the frog Hydrophylax bahuvistara and their analogs (B1A1, B2A1, B1A2, B2A2) were tested against two multi host Gram-negative pathogens such as Pseudomonas aeruginosa and Vibrio vulnificus. The combined effect of peptides with known antibiotics (kanamycin, ciprofloxacin, and tetracycline) was also tested in different pH and serum concentrations. The parent peptides were active against V. vulnificus, but their modified analogs did not improve the activity. In P. aeruginosa, the parent peptides showed weak activity, but their modified analogs showed increased activity. The peptides were found to be hemolytic (18 to 50%). A synergistic interaction was observed when combining the peptides with traditional antibiotics resulted in the 4–25 fold reduction of MICs, which indicates an overall increase in the activity in low doses of both peptides and antibiotics. The parent peptide B2 showed synergy with tetracycline and ciprofloxacin against V. vulnificus. B1A1 and B2A1 showed synergy with all the antibiotics tested against V. vulnificus. B1A2 showed synergy with kanamycin against P. aeruginosa, while B2A2 showed synergistic relation with kanamycin and ciprofloxacin against P. aeruginosa. As a result, the percentage of hemolysis and the time needed for the bacterial killing was reduced notably. The activity was retained in different concentrations of cation, pH, and serum. These findings in the present study also highlight the influence of the modification of natural peptides for improved activity against Gram-negative bacteria and may verify the importance of combinatorial therapy of peptide-antibiotic combinations in the fight against drug-resistant pathogens.