Allium-Derived Compounds Against Multidrug-Resistant Bacteria: Antibacterial Activity and Synergistic Effects

Antibiotic resistance is a major global health challenge, driven by misuse in medicine and agriculture and the scarcity of new drugs. Allium-derived organosulfur molecules have shown antimicrobial and synergistic effects with antibiotics. This study aimed to evaluate the in vitro antibacterial activity of four Allium-derived compounds and their potential synergy with clinical antibiotics against multidrug-resistant bacteria.

A total of 330 multidrug-resistant clinical isolates were analyzed, including Gram-positive cocci and Gram-negative bacilli. Antibacterial activity of propyl-propane-thiosulfinate, propyl-propane-thiosulfonate (PTSO), butyl-butane-thiosulfinate, and butyl-butane-thiosulfonate was determined by broth microdilution. Synergy with conventional antibiotics was assessed in 24 representative isolates using the checkerboard method, with interactions classified by the fractional inhibitory concentration index.

PTSO exhibited the highest activity, with MIC₅₀ of 4-8 µg/mL and MIC₉₀ up to 8 µg/mL against S. aureus, E. faecalis, and S. agalactiae. Activity against Gram-negative bacteria was limited, though PTSO was the most active. Checkerboard assays showed predominantly indifferent interactions, but partial synergy with aminoglycosides was observed in both Gram-positive and Gram-negative bacteria.

PTSO demonstrated the most significant activity against multidrug-resistant Gram-positive bacteria, with limited impact on Gram-negative strains, and partial synergy with aminoglycosides suggests a potential role for combination therapy.