Antimicrobial and anti-biofilm activities of Vernonia amygdalina and Senna siamea leaf extracts against pathogenic bacteria

The study assessed the antibacterial and antibiofilm capability of Vernonia amygdalina and Senna siamea against both ESBL- and non-ESBL-producing bacteria. The result from the phytochemical screening revealed that secondary metabolites such as alkaloids, flavonoids, saponins, tannins, coumarins, triterpenoids, and phytosteroids were present in both plants, except glycosides, which were exclusively detected in Vernonia amygdalina. The antibacterial activity showed that Senna siamea had its highest zone of inhibition against K. pneumoniae, whereas Vernonia amygdalina recorded its highest effect on E. coli. The MIC values for Senna siamea ranged from 6.25 to 25.00 mg/mL, while the MICs of Vernonia amygdalina ranged from 12.50 ± 0.00 to 50.00 ± 0.00 mg/mL. Combination testing indicated synergy between the two extracts only for E. coli. Antibiofilm assays showed clear dose-dependent inhibition. At 100 mg/mL, Vernonia amygdalina showed 99.01% inhibition against ESBL K. pneumoniae, while Senna siamea at the same concentration reached 99.72% against S. aureus. These data demonstrate the relevant antibacterial and antibiofilm activities for each extract and support continuing efforts that could include them in new strategies against resistant pathogens, including ESBL-producers.