Increased Staphylococcus-killing activity of an antimicrobial peptide, lactoferricin B, with minocycline and monoacylglycerol

This study aimed to find antibiotics or other compounds that could increase the antimicrobial activity of an antimicrobial peptide, lactoferricin B (LFcin B), against Staphylococcus aureus, including antibiotic-resistant strains. Among conventional antibiotics, minocycline increased the bactericidal activity of LFcin B against S. aureus, but methicillin, ceftizoxime, and sulfamethoxazole-trimethoprim did not have such an effect. The combination of minocycline and LFcin B had synergistic effects against three antibiotic-resistant strains of S. aureus, according to result of checkerboard analysis. Screening of 33 compounds, including acids and salts, alcohols, amino acids, proteins and peptides, sugar, and lipids, showed that medium-chain monoacylglycerols increased the bactericidal activity of LFcin B against three S. aureus strains. The short-term killing test in water and the killing curve test in growing cultures showed that a combination of LFcin B and monolaurin (a monoacylglycerol with a 12-carbon acyl chain) killed S. aureus more rapidly than either agent alone. These findings may be helpful in the application of antimicrobial peptides in medical or other situations.