Antibacterial, Antioxidant activities, and phytochemical content of Piliostigma thonningii (Schumach) Milne-Redh and Piliostigma reticulatum (DC) Hochst from Lubumbashi, in Democratic Republic of Congo

Background: Piliostigma thonningii (Schumach.) Milne‐Redh and Piliostigma reticulatum (DC.) Hochst. are widely employed in Katangan traditional medicine to treat respiratory and urinary tract disorders. This study evaluated the in vitro antibacterial, antioxidant and safety profiles of crude leaf, stem-bark and root extracts of both species, alongside their phytochemical composition.

Methods: Extracts were screened against six bacterial pathogens—Escherichia coli, Salmonella typhi, Shigella sonnei, Staphylococcus aureus, Klebsiella pneumoniae and Streptococcus pneumoniae—using broth microdilution to determine minimum inhibitory concentrations (MIC) and agar diffusion to measure inhibition zones. Radical-scavenging activity was assessed by the DPPH assay. Total polyphenol and flavonoid contents were quantified spectrophotometrically (expressed as mg gallic acid equivalents [GAE]/g and mg quercetin equivalents [QE]/g, respectively). Acute oral toxicity was conducted according to OECD Guideline 423, with haematological and biochemical parameters monitored post-dosing. Physicochemical quality of the powdered plant drugs was evaluated by total ash and titratable acidity determinations.

Results: All extracts exhibited significant antibacterial activity, with MIC values ranging from 15 to 250 µg/mL. The most pronounced activity was observed against E. coli and K. pneumoniae (MIC = 15.625 µg/mL; Inhibition zone diameter :12–19 mm). Extracts displayed potent antioxidant capacity (IC₅₀ = 2.4–5 µg/mL). No acute toxicity or adverse alterations in haematological or biochemical markers were detected at the tested doses. Phytochemical analysis revealed total polyphenol contents of 47–578 mg GAE/g and total flavonoid contents of 30–435 mg QE/g across all organs. The powdered drugs contained 7–10 % total ash and exhibited titratable acidity of 2.3–3.6 mg/g.

Conclusion: The demonstrated antibacterial and antioxidant activities, coupled with a favourable safety profile, substantiate the traditional use of P. thonningii and P. reticulatum in managing bacterial infections and support their further development as phytomedicinal agents.