Biological Activities of Leonotis ocymifolia (Burm.f.) and Its Antibacterial Activities Against ESKAPE Pathogens.

Background/Objectives: The rise in antibiotic-resistant ESKAPE pathogens, which are responsible for severe and hard-to-treat infections, highlights the urgent need for alternative therapeutic agents. While species in the Leonotis genus have demonstrated antimicrobial potential, limited research exists on Leonotis ocymifolia. This study evaluated the phytochemical profiles and antioxidant, antibacterial, and antibiofilm activities of L. ocymifolia leaf and stem extracts. Methods: Acidified acetone and hexane were used for extraction, followed by liquid-liquid fractionation with dichloromethane (DCM), ethyl acetate, and butanol. Phytochemicals were profiled using thin-layer chromatography (TLC), while polyphenolic content and antioxidant activity were determined using colorimetric and DPPH assays, respectively. Antibacterial activity was assessed via bioautography and micro-broth dilution assays. Antibiofilm activities were evaluated using crystal violet staining, and metabolic activity was assessed using tetrazolium salt as a cell viability indicator. Results: Ethyl acetate fractions had the highest phenolic (98.15 ± 9.63 mg GAE/g) and tannin contents (108.28 ± 8.78 mg GAE/g), with strong DPPH scavenging activity (79-90% at 250 µg/mL). DCM extracts had potent antibacterial activity, with a minimum inhibitory concentration (MIC) of 0.31-0.625 mg/mL against Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae. Antibiofilm assays revealed over 50% inhibition across biofilm formation phases, with DCM leaf extracts disrupting biofilms by inhibiting microbial metabolism. Conclusions: This study highlights L. ocymifolia as a promising source of bioactive compounds with significant antioxidant and antibacterial properties. The DCM and ethyl acetate extracts demonstrated high polyphenol content and effective biofilm inhibition. Further studies are warranted to isolate bioactive compounds and elucidate their mechanisms of action.