Antimicrobial effect and proposed action mechanism of cordycepin against Escherichia coli and Bacillus subtilis

The detailed antibacterial mechanism of cordycepin efficacy against food-borne germs remains ambiguous. In this study, the antibacterial activity and action mechanism of cordycepin were assessed. The results showed that cordycepin effectively inhibited the growth of seven bacterial pathogens including both Gram-positive and Gram-negative bacterial pathogens; the minimum inhibitory concentrations (MIC) were 2.5 and 1.25 mg/ml against Escherichia coli and Bacillus subtilis, respectively. Scanning electron microscope and transmission electron microscope examination confirmed that cordycepin caused obvious damages in the cytoplasmatic membranes of both E. coli and B. subtilis. Outer membrane permeability assessment indicated the loss of barrier function and the leakage of cytoplasmic contents. Propidium iodide and carboxyfluorescein diacetate double staining approach coupled with flow cytometry analysis indicated that the integrity of cell membrane was severely damaged during a short time, while the intracellular enzyme system still remained active. This clearly suggested that membrane damage was one of the reasons for cordycepin efficacy against bacteria. Additionally, results from circular dichroism and fluorescence analysis indicated cordycepin could insert to genome DNA base and double strand, which disordered the structure of genomic DNA. Basis on these results, the mode of bactericidal action of cordycepin against E. coli and B. subtilis was found to be a dual mechanism, disrupting bacterial cell membranes and binding to bacterial genomic DNA to interfere in cellular functions, ultimately leading to cell death.