Z-Amino Acids Present Innovative Antimicrobial and Antibiofilm Properties against Methicillin-Susceptible and -Resistant <i>Staphylococcus aureus</i>

One of the challenges associated with bacteria is their ability to form biofilms that can grow on medical equipment, resulting in more severe and persistent infections. Unfortunately, most antibiotics are optimized for planktonic bacteria, and their therapeutic window is limited when targeting biofilms. Eradicating biofilms typically requires concentrations that are much higher than the minimum inhibitory concentration (MIC), increasing the concern about cytotoxicity toward mammalian cells. In this study, benzyloxycarbonyl-protected amino acids (Z-amino acids), for the first time, were analyzed for both antimicrobial and antibiofilm activity against <i>Staphylococcus aureus</i> (<i>S. aureus</i>), a strain prevalent in surgical infections. It was determined that Z-amino acids, especially Z-glycine (Z-Gly), exhibited fast antimicrobial properties against <i>S. aureus</i>, causing early depolarization and leading to enhanced membrane permeability. Severe membrane disruption of <i>S. aureus</i> after treatment with Z-glutamine (Z-Gln) was confirmed microscopically. Additionally, Z-amino acids effectively inhibited biofilm formation at 1× MIC and dispersed mature biofilms at 2× MIC. Notably, Z-Gln had the most favorable antimicrobial activity profile with minimal toxicity toward mammalian cells at both 1× and 2× MIC. These concentrations were effective against both planktonic and biofilm-associated bacteria while maintaining at least 80% viability of osteoblast cells after a 24 h exposure. These Z-amino acids also exhibited similar toxicity toward epithelial cells (e.g., BEAS-2B cells), indicating a consistent safety profile against different cell types. These findings suggest that Z-amino acids, particularly Z-Gln, show promise as a new therapeutic agent that targets both planktonic and biofilm-associated infections.