Species-Dependent Effects of 3-Hydroxychromone Derivatives on Biofilm Biomass and Planktonic Growth

A series of 3-hydroxychromone derivatives bearing Mannich-type motifs was synthesized and evaluated for effects on biofilm-associated biomass and planktonic growth in Staphylococcus aureus ALC2085 and Pseudomonas aeruginosa PAO1. Compounds were initially screened at 20 μg/mL using crystal violet staining, followed by experimental 50% growth-inhibitory concentration (GIC50) and CFU analyses. Against S. aureus, aryl-substituted derivatives had GIC50 values >200 μg/mL, whereas 6-bromo derivatives had values of 1.25–10 μg/mL. Thus, the biomass reductions produced by NSK 18 at 20 μg/mL could not be separated from planktonic growth inhibition. Against PAO1, NSK 16 produced statistically significant decreases in biomass, reducing it to 50 ± 24% of the untreated control (p = 0.03584), without comparably large or sustained reductions in the measured planktonic-growth endpoints at 20 μg/mL. These findings demonstrate species- and substitution-dependent activity and identify NSK 16 as preliminary PAO1 biomass-reducing hits. Because biomass was measured at a single concentration and not normalized to growth under matched conditions, further concentration-response and viability studies are required to establish biofilm selectivity.