Cynaroside targets distinct metabolic pathways in gram-positive and gram-negative pathogenic bacteria: an integrated...

The antibiotic resistance crisis has become a major threat to global public health. Discovering natural antibacterial compounds with unique mechanisms from traditional medicinal plants is an effective strategy to overcome this challenge. Through activity-guided fractionation, three compounds were isolated from Turpinia arguta leaves, identified as piperyamine A, cynaroside, and gallic acid. Cynaroside exhibited the strongest antibacterial activity, with MIC values of 31.25 μg/mL against Staphylococcus aureus (Gram-positive) and 62.5 μg/mL against Vibrio parahaemolyticus (Gram-negative). Phenotypic experiments, including scanning electron microscopy, electrical conductivity measurements, and alkaline phosphatase (ALP) activity assays, were performed to evaluate antibacterial effects of cynaroside. The results indicated that cynaroside exerted antibacterial effects by disrupting the integrity of bacterial cell walls and cell membranes, with markedly different responses between Gram-positive and Gram-negative bacteria. Specifically, the increase in electrical conductivity was more pronounced in V. parahaemolyticus (Gram-negative), while the peak ALP activity was higher in S. aureus (Gram-positive). Integrated metabolomic and transcriptomic analyses were conducted to elucidate the differential antibacterial mechanisms. In S. aureus, cynaroside treatment was associated with suppression of pyrimidine metabolism and histidine metabolism, negatively regulating 11 metabolites with pyrC as the hub gene; in V. parahaemolyticus, it mainly inhibited glyoxylate and dicarboxylate metabolism and branched-chain amino acid degradation, negatively regulating tricarboxylic acid cycle intermediates with fdh3B as the hub gene. This study reveals the differential antibacterial mechanisms of cynaroside isolated from Turpinia arguta against Gram-positive and Gram-negative bacteria, laying a theoretical foundation for the development of species-selective natural antibacterial agents.