Killing of stationary staphylococcus aureus within microaggregates and macrophages by free sitafloxacin and sugar, or as carrier-free nanodrug.

Staphylococcus aureus infections often develop biofilms, abscesses, and intracellular reservoirs, which reduce antibiotic effectiveness. This reduced efficacy is partly due to bacterial metabolic inactivity. However, sugars can reactivate bacteria and restore their susceptibility. This study aims to identify effective combination of sitafloxacin and sugars and develop a carrier-free nanodrug delivery system to enhance treatment against metabolically inactive S. aureus. Sitafloxacin demonstrates the highest activity against stationary-phase USA300 S. aureus, achieving a ∼3 log10 bacterial reduction, which is more than tenfold enhanced when combined with glucose, fructose, or mannose. The antibacterial effects were confirmed in biofilm and abscess in vitro models, with sugars potentiating sitafloxacin in abscesses. Nanodrugs were synthesized by covalently linking sitafloxacin to sugars via Schiff-base bonds, allowing self-assembly into stable nanoparticles (∼100 nm). Antibiotic release reaches ∼35-40% over three days at physiological pH, indicating high stability. These nanodrugs reduce stationary and growing bacteria and in vitro abscesses by ∼2 log10 and biofilm bacteria by ∼4 log10, needing further refinement to achieve enhanced activity compared to free sitafloxacin. They accumulate in macrophages, reducing intracellular bacteria by 2 log10 without any cytotoxic effect. This novel nanosystem co-delivers antibiotic and sugar without inert carriers, demonstrating antimicrobial activity, biocompatibility, and delayed release, offering potential for targeting persistent bacterial infections.