Antimicrobial activity of cultivated cardoon (Cynara cardunculus L. var. altilis DC.) leaf extracts against bacterial species of agricultural and food interest

The growth inhibition of bacterial species through bioactive natural compounds is an already consolidated purpose in the scientific community, with the dual aim to reduce environmental and health hazards derived from synthetic products and to manage the increasing diffusion of antimicrobial resistance. Aqueous, methanolic and ethanolic extracts at two different concentrations from cultivated cardoon leaves (Cynara cardunculus L. var. altilis DC.) were assessed in vitro for antimicrobial activity against eleven Gram positive and negative bacterial species of agriculture and food interest: Bacillus megaterium, Rhodococcus fascians, Xanthomonas perforans, Pseudomonas syringae pv. tomato, Escherichia coli, Salmonella enterica, Pseudomonas fluorescens, Listeria innocua, Staphylococcus aureus, Bacillus subtilis, and Bacillus cereus. The ethanolic extract was found to be the most active, followed by the methanolic and aqueous ones. All the extracts at the highest concentrations were able to effectively inhibit the growth of Gram positive species. For what concerning Gram negative bacteria, the methanolic extract was not effective, the ethanolic showed detectable antibacterial activity at both concentrations, and the aqueous evidenced inhibitory activity only against P. syringae and X. perforans when tested at the highest concentration. On the basis of HPLC analysis on dried leaves, identified compounds were caffeoylquinic acids (chlorogenic acid, 1,5-O-dicaffeoylquinic acid and monosuccinildicaffeoylquinic acid, representing more than 50% of the total measured polyphenols), luteolin and apigenin derivatives, and the sesquiterpene lactone cynaropicrin.