Therapeutic Potential of Clerodendrum glabrum and Gardenia volkensii Acetone Extracts: Antioxidant, Antibacterial, and Anti-Virulence Activities

Background/Objectives: Antibiotic-resistant bacteria pose a global health threat, driving the need for alternative treatments. Medicinal plants such as Clerodendrum glabrum and Gardenia volkensii are promising sources of bioactive compounds. This study evaluated the antioxidant, antibacterial, and anti-virulence activities of their acetone extracts, comparing sonication and conventional shaking extraction methods. Methods: Colorimetric methods assessed total polyphenol content. Antioxidant activity was measured using 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and hydrogen peroxide (H2O2) assays. Antibacterial effects against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes were analysed through broth microdilution, total activity, growth kinetics, and combinational studies. Anti-virulence activity was assessed via biofilm biomass inhibition, metabolic activity and anti-swarming assays. Results: Phenolics were the most abundant phytochemicals, followed by flavonols. C. glabrum exhibited strong antioxidant activity in both DPPH and H2O2 assays. MIC values ranged from 0.16 to 2.5 mg/mL, with the shaken G. volkensii leaf extract showing the highest total activity (575 mL/g) against E. coli. A combination of G. volkensii leaf extract and gentamicin resulted in an additive antibacterial effect. All extracts prevented the formation of biofilm biomass in all tested microorganisms (inhibition > 50%) except for extracts obtained by sonication. The sonicated leaf extract of C. glabrum inhibited initial E. coli attachment. Additionally, the sonicated leaf extract of C. glabrum inhibited P. aeruginosa motility. Conclusions: These findings suggested that a targeted approach based on plant species and extraction methods could improve treatment outcomes against biofilm-associated pathogens. Notably, acetone extracts derived from C. glabrum and G. volkensii exhibit considerable potential as natural sources of antioxidant, antibacterial, and anti-virulence agents effective against nosocomial infections.