Antimicrobial resistance modifying effects and molecular docking studies of Affinine, derived from Tabernaemontana crassa

• T. crassa extracts showed antimicrobial and resistance modifying effects. • Affinine, a monoterpene indole alkaloid isolated from T. crassa , inhibited efflux pump and biofilm formation in the tested microorganisms. • In silico studies, elucidated the mechanisms by which affinine exerts these resistance modifying effects. Tabernaemontana crassa is a native plant indigenous to Ghana which has garnered local recognition for its purported efficacy against ringworm, wounds, abscesses, and antibacterial infections. However, the antibacterial and resistance modifying effects of the crude extracts and isolated compounds have not been investigated. Consequently, this study aims to evaluate the antimicrobial and resistance modifying effects of the extracts and affinine, a monoterpene indole alkaloid, from T. crassa . Four extracts, namely the crude, alkaloidal, glycosidic and triterpene fractions were prepared by solvent-solvent extraction from the stem bark of T. crassa . Using chromatographic and spectroscopic techniques, affinine was isolated and identified from the alkaloidal fraction. The effects of the extracts and affinine were investigated using the micro dilution, efflux pump and biofilm inhibition assays against Staphylococcus aureus and Pseudomonas aeruginosa. The crude extracts were effective against the two bacteria strains at a concentration of 500 µg/ml. Affinine was without activity in the in vitro antimicrobial assays with MIC >1000 µg/ml. However, affinine possessed anti-efflux and antibiofilm activity against the test microorganisms which was confirmed with in silico studies. The study showed the efficacy of the extracts against the two microbes associated with wound healing. Affinine, not previously described from T. crassa , may contribute to the anti-infective effects of the plant.