In Vitro Evaluation of the Antibacterial and Antioxidant Activities of Extracts From Five Medicinal Plants Traditionally Used to Treat Infections in Burundi

Infectious diseases periodically emerge or re-emerge, causing epidemics or pandemics that significantly impact global health. While hygiene measures and antibiotics have improved infection control, the rapid spread of antimicrobial resistance remains a major threat. In this context, extracts from five plants used in traditional Burundian medicine (Mikania natalensis DC., Helichrysum congolanum Schltr. & O. Hoffm., Justicia nyassana Lindau, Urtica massaica Mildbr., and Senecio maranguensis O. Hoffm.) were evaluated for their antibacterial and antioxidant potential. Antibacterial activities were assessed on fifteen bacterial strains using microdilution method and TLC-bioautography, while antioxidant activity was assessed through the DPPH• radical scavenging method. Gram-positive strains, particularly S. aureus, showed greater sensitivity compared to Gram-negative bacteria. Four plants exhibited active extracts with MICs between 250 and 1000 µg/mL, except for S. maranguensis (MICs ≥ 2000 µg/mL). M. natalensis was the most active, with dichloromethane and ethyl acetate extracts showing MICs of 250 and 500 µg/mL. Beyond their intrinsic antibacterial activity, this study reveals that otherwise inactive extracts of M. natalensis can significantly potentiate β-lactam and aminoglycoside antibiotics against multidrug-resistant S.aureus, highlighting a previously underexplored resistance-modulating effect. Methanolic extracts of all five plants displayed modest antioxidant activity, with IC₅₀ values, expressed as quercetin equivalents (IC₅₀ QE) ranging from < 0.08 to 0.169±0.0065. These findings highlight the potential of Burundian medicinal plants in combating antibiotic resistances, though the use of S. maranguensis should be carefully reevaluated, given the well-known occurrence of genotoxic and hepatotoxic pyrrolizidine alkaloids in the genus.