Deep Eutectic Solutions for Microbial Problems – Recent Advances in the Use of Deep Eutectic Solvents as Direct/Indirect Antimicrobial Agents and Guidelines for Assessing Their Antimicrobial Activity

The rise of antimicrobial resistance (AMR) urges the search for alternatives beyond conventional antibiotics. Deep eutectic solvents (DESs) have gained attention in biomedicine due to their tunable properties, ease of preparation, and stability. In the antimicrobial field, DESs play a dual role: they can display intrinsic activity when composed of bioactive constituents, or act as enabling vehicles that enhance the solubility, stability, and bioavailability of other agents. This review outlines current advances in both direct and indirect antimicrobial effects of DESs in widely defined antimicrobial applications. Herein, we summarize how composition of “free” DESs govern activity against Gram (+) and Gram (–) bacteria, as well as yeasts and filamentous fungi. Moreover, we also focus on representative examples where DESs enhance the performance of antibiotics, peptides, and phytochemical extracts. Special attention is also given to methodological aspects, including variability in antimicrobial testing protocols and the current scarcity of systematic cytotoxicity and in vivo data – based on which we propose a unified workflow for future antimicrobial testing of DESs. Altogether, this review captures the progress made over the last three years and aims to help systematize current knowledge in this (still emerging) field.