Breaking through Microbial Defenses─Organic Acid-Based Deep Eutectic Solvents as a Neoteric Strategy in Bacterial Biofilms, Persister, and Fungal Control

This study explores the adaptation of organic acid-based deep eutectic solvents (OA-DESs) as effective antimicrobial agents. Having already demonstrated their efficacy against planktonic bacteria in our previous research, herein we investigate their impact on more complex microbial forms, including biofilms, persister cells, and fungi (both human pathogenic and phytopathogenic). Our experiments revealed that OA-DESs effectively eradicated methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) and <i>Escherichia coli</i> in the biofilms, inducing significant morphological changes. A three-log-unit reduction was observed for most OA-DESs at concentrations below 1% (v/v), a remarkable achievement for this class of materials. Additionally, with only one exception, OA-DESs did not promote persister cells formation, underscoring their potential for complete eradication of biofilm-enveloped bacteria. In another part of our study, OA-DESs were compared to conventional DESs against <i>Candida albicans</i>, <i>Candida auris</i>, and <i>Aspergillus fumigatus</i>. Results showed that while individual DES components exhibited minimal activity, their combination effectively inhibited fungal growth and induced substantial morphological changes. Lastly, OA-DESs were tested against the phytopathogens <i>Zymoseptoria tritici</i> and <i>Venturia inaequalis</i>. Though their activity was less pronounced compared to pathogenic strains, most OA-DESs inhibited the growth of both fungi at the highest tested concentrations. Despite the broad scope of this investigation, we believe this work provides valuable insights into the potential of DESs as antimicrobial agents, offering a strong foundation for future research and innovation in this field.