Fatty acid modified-antimicrobial peptide analogues with potent antimicrobial activity and topical therapeutic efficacy against Staphylococcus hyicus.

There is an urgent need to explore new antimicrobial agents due to the looming threat of bacteria resistance. Bovine lactoferricin (LfcinB), as a multifunctional peptide, has the potential to be a new active drug in the future. In this study, it aims to investigate the effect of fatty acid conjugation on antimicrobial peptide activity and topical therapeutic efficacy in a mouse model infected with Staphylococcus hyicus. Both Lfcin4 and Lfcin5 were conjugated with the unsaturated fatty acid linoleic acid (18-C) at their N-terminus and modified by acylation at the C-terminus. The derived peptides of Lin-Lf4NH2 and Lin-Lf5NH2 showed better antibacterial activity (MICs of 3.27 to 6.64 μM) than their parent peptides (MICs of 1.83 to 59.57 μM). Lin-Lf4NH2 (63.2%, 5 min) and Lin-Lf5NH2 (35.8%, 5 min) could more rapidly penetrate bacterial membrane than Lf4NH2 (2.34%, 5 min) and Lf5NH2 (1.94%, 5 min), which further confirmed by the laser scanning confocal microscopy (LSCM). Electron microscopy observations showed Lin-Lf4NH2 and Lin-Lf5NH2 disrupted S. hyicus cell membranes and led to the leakage of contents. Furthermore, after treatment with Lin-Lf4NH2 and Lin-Lf5NH2, the abscess symptoms of mice were significantly alleviated; the recovery rate of abscesses scope of Lin-Lf4NH2 (73.25%) and Lin-Lf5NH2 (71.71%) were 38.8 and 37.9-fold higher than that of untreated group (1.89%), respectively, and superior to Lf4NH2 (46.87%) and Lf5NH2 (58.75%). They significantly reduced the bacterial load and the levels of the pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) and chemokine (MCP-1) in S. hyicus skin lesions. This study provides evidence that conjugation of a fatty acid to antimicrobial peptides can improve the activity and have potential for topical therapeutic of S. hyicus skin infections. KEY POINTS: • Lin-Lfcin4NH2/Lfcin5NH2 showed stronger antimicrobial activity than parent peptides. • Lin-Lfcin4NH2/Lfcin5NH2 had a more effective ability to destroy bacterial membranes. • Lin-Lfcin4NH2/Lfcin5NH2 showed a topically higher efficacy than parent peptides.