Antimicrobial resistance is listed by the World Health Organization (WHO) as one of the ten main global health threats. It is estimated that by 2050, this problem will cause the loss of 10 million lives per year due to the emergence of multidrug-resistant microorganisms, making the search for new therapeutic alternatives urgent. In this context, the investigation of medicinal plants combined with antibiotic action is highly promising. The objective of this study was to evaluate the synergistic potential between Sparattosperma leucanthum and vancomycin against Staphylococcus aureus ATCC 25923.

Leaf extracts were prepared using hexane, dichloromethane, ethyl acetate, and methanol for the determination of the minimum inhibitory concentration (MIC₁₀₀) against S. aureus. The most active extract was selected for evaluation of its synergistic potential with vancomycin using the checkerboard technique. Extract concentrations ranged from 1.95 to 250 µg/mL, and vancomycin concentrations from 0.0005 to 0.075 µg/mL, resulting in 64 combinations of both agents. Inoculum standardization, incubation, and controls followed CLSI procedures. All assays were performed in triplicate. Results were calculated using the fractional inhibitory concentration index (FICI): FICI ≤ 0.9 = synergistic effect; 0.9 < FICI < 1.1 = additive effect; FICI > 1.1 = antagonistic effect.

The most active extract was the dichloromethane extract, which presented an isolated MIC of 250 μg/mL and remained unchanged during the synergy evaluation. The isolated MIC of vancomycin was 0.0375 µg/mL, and when combined with the extract, it was reduced to 0.004 µg/mL. The FICI was 1.1, indicating a relevant additive effect between vancomycin and the extract, which reduced the antibiotic concentration by more than ninefold.

The combined action between antibiotics and plant extracts represents a relevant alternative for the treatment of infectious diseases, potentially contributing to controlling the advancement of antimicrobial resistance.