Structure-Activity Study of the Antimicrobial Lipopeptide Humimycin A and Screening Against Multidrug-Resistant .

BACKGROUND

The emergence of multidrug-resistant (MDR) presents a critical global health challenge due to treatment failures and high mortality rates. Faced with this growing threat, new antimicrobials with original modes of action are urgently needed, and antimicrobial peptides proved to be promising alternatives.

OBJECTIVES

The aim of this study is to explore the structure-function relationship of the lipopeptide humimycin A, compare the spectrum of activity of the synthetic analogs against a panel of isolates, and investigate their binding to the humimycin target, the lipid II flippase MurJ.

METHODS

Humimycin A and 15 analogs were produced by solid-phase peptide synthesis, and their antimicrobial activity was evaluated by agar diffusion and microtitration assays against 19 isolates from bovine mastitis and other pathogens.

RESULTS

Among the synthesized peptides, four humimycin analogs exhibited activity against methicillin-sensitive and methicillin-resistant , as well as several isolates in the panel, including MDR , with minimal inhibitory concentration values ranging from 0.5 to 256 µg/mL. Results from the structure-activity relationship study showed that the β-hydroxymyristoyl lipid chain and C-terminal carboxylic acid are essential for antimicrobial efficacy. In presence of human erythrocytes, the active humimycin analogs exhibited moderate hemolytic activity, suggesting selectivity indexes ranging from 3 to 27 against the more sensitive strains. Critical micelle concentration measurements elucidated micelle formation and proved to not be essential for the antibacterial activity. Molecular docking and 100 ns simulations with the lipid II flippase MurJ (PDB: 5T77) provided favorable binding energy.

CONCLUSIONS

The findings underscore the potential of humimycin analogs as antimicrobials for preventing and treating MDR infections in veterinary, animal husbandry, and human medicine.