Environmental and Chemical Modulation of Staphylococcus aureus Newman Biofilm Formation

Staphylococcus aureus biofilm formation enhances survival on host tissues and medical devices. This study tested how oxidative stress (H₂O₂), pH (5–9), NaCl (0–10%), and human serum (5–50%) affect Newman strain biofilm and key genes ( icaA , icaD , sarA ). Biofilm was quantified by crystal violet assays, and gene expression measured by quantitative real-time PCR. Biofilm biomass was quantified using crystal violet staining assays under various environmental conditions. Statistical significance was determined using ANOVA with post-hoc analysis ( p  < 0.05). Hydrogen peroxide induced a dose-dependent reduction in biomass, with significant repression of icaA, icaD , and sarA expression at 3% H₂O₂ (≤ 22.8%, p  < 0.01). Similarly, deviations from neutral pH markedly impaired biofilm formation, with acidic (pH 5) and alkaline (pH 9) conditions reducing biomass by 34.6% and 41.7%, respectively, accompanied by strong downregulation of biofilm-associated genes ( p  < 0.001). In contrast, NaCl exerted a biphasic effect: mild osmotic stress (1.25% and 5%) enhanced biofilm biomass (up to 154.2%) and gene expression ( icaA 160.55%, icaD 168.18%, sarA 149.8%, p  < 0.01), whereas higher concentrations (≥ 10%) restored expression to near-control levels. Serum exposure produced a threshold-dependent response, with low concentrations (5–10%) slightly enhancing gene expression (~ 110%), while higher concentrations (20–50%) significantly repressed both biomass and transcription, with profound inhibition observed at 50% ( icaA 12.94%, icaD 10.88%, sarA 12.79%, p  < 0.001). Environmental stressors modulate Staphylococcus aureus biofilm formation in a dose-dependent manner via regulation of the ica operon and sarA , offering molecular insights that may guide strategies for biofilm control.