Antimycobacterial Mechanisms and Anti-Virulence Activities of Polyphenolic-Rich South African Medicinal Plants Against Mycobacterium smegmatis

The rise of multidrug-resistant tuberculosis (TB) necessitates alternative therapeutic sources. This study investigated the polyphenolic content and the antioxidant, antimycobacterial, and anti-virulence activities of selected medicinal plants traditionally used to treat TB and related symptoms. Total phenolics, tannins, and flavonoids were quantified using colorimetric assays. Antioxidant capacity was assessed via DPPH and ferric-reducing power assays. Antimycobacterial activity against <i>Mycobacterium smegmatis</i> was evaluated using broth microdilution, growth kinetics, cell constituent leakage, and respiratory chain dehydrogenase inhibition assays. Anti-virulence effects were examined using crystal violet biofilm and swarming motility assays. <i>Tarchonanthus camphoratus</i> showed the highest polyphenolic levels and, together with <i>Combretum hereroense</i>, strong antioxidant activity. Extracts of <i>Senecio macroglossus</i>, <i>Nerium oleander</i>, and <i>Tetradenia riparia</i> displayed potent antimycobacterial activity (MIC = 0.16 mg/mL), characterized by delayed exponential growth, membrane damage, and metabolic inhibition. <i>Tabernaemontana elegans</i> exhibited the weakest activity (MIC > 2.5 mg/mL). Most extracts also significantly impaired motility (12-100%) and early-stage biofilm formation. Polyphenolic-rich plant extracts demonstrated promising antimycobacterial and anti-virulence properties against <i>M. smegmatis</i>, highlighting their potential as leads for developing novel anti-TB agents.