Antibacterial activity and mode of action of selected glucosinolate hydrolysis products against bacterial pathogens

Abstract

Plants contain numerous components that are important sources of new bioactive molecules with antimicrobial properties. Isothiocyanates (ITCs) are plant secondary metabolites found in cruciferous vegetables that are arising as promising antimicrobial agents in food industry. The aim of this study was to assess the antibacterial activity of two isothiocyanates (ITCs), allylisothiocyanate (AITC) and 2-phenylethylisothiocyanate (PEITC) against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes. The antibacterial mode of action was also characterized by the assessment of different physiological indices: membrane integrity, intracellular potassium release, physicochemical surface properties and surface charge. The minimum inhibitory concentration (MIC) of AITC and PEITC was 100 μg/mL for all bacteria. The minimum bactericidal concentration (MBC) of the ITCs was at least 10 times higher than the MIC. Both AITC and PEITC changed the membrane properties of the bacteria decreasing their surface charge and compromising the integrity of the cytoplasmatic membrane with consequent potassium leakage and propidium iodide uptake. The surface hydrophobicity was also non-specifically altered (E. coli and L. monocytogenes become less hydrophilic; P. aeruginosa and S. aureus become more hydrophilic). This study shows that AITC and PEITC have strong antimicrobial potential against the bacteria tested, through the disruption of the bacterial cell membranes. Moreover, phytochemicals are highlighted as a valuable sustainable source of new bioactive products.

Biosynthesis and bioactivity of glucosinolates and their production in plant in vitro cultures

“…Moreover, the interaction between isothiocyanate groups and thiol or amine groups of microbial proteins may induce oxidative stress responses and alter cellular redox homeostasis (Dufour et al 2015). In this sense, aromatic glucosinolate-derived isothiocyanates had higher levels of reactivity due to their ability to act as electron donors from the benzene ring (Borges et al 2015). Borges et al (2015) also found that isothiocyanates can act on bacterial cell membranes because these compounds are able to interact with external membrane proteins and penetrate into the cytoplasm, decreasing bacterial growth and leading to their death.…”

Gut Glucosinolate Metabolism and Isothiocyanate Production

“…Of interest is the effect that ITC‐producing bacteria have on other microorganisms of the human gut. ITCs are known to have antibacterial properties and it is possible that there may be an overall negative effect on other functions of the gut microbiota. This however, would be dependent on the concentrations of ITCs in the human gut and as yet this question has not been fully addressed .…”

The Glucosinolates, A Sulphur Glucoside Family of Mustard Phytochemicals With Diverse Biomedical Application

“…Significantly, the activated glucosinolates appear applicable to the treatment of human infections and may be used in combination therapy with existing antibiotics. Comparison of the antibiotic activities of SFN and AITCs with that of Vancomycin showed that all contained significant bactericidal activity [4,7,11,65,78]. Sulphoraphane was at least as effective an antibiotic as Vancomycin and was more potent in all bacteria tested.…”

“…The myrosinase-glucosinolate system evolved in plants of the Capparales order as a protective mechanism aimed against, bacterial and fungal infection and attack by parasites or insects [4,7,11,65,78]. Significantly, the activated glucosinolates appear applicable to the treatment of human infections and may be used in combination therapy with existing antibiotics.…”

“…Plants produce a myriad of phytochemicals and many of these have valuable nutritive, medicinal and health promoting properties [1][2][3]. Anecdotal evidence often points to these beneficial properties however in this report we will concentrate on one family of molecules, the glucosinolates, a family of Sulphur containing glucosides with a very extensive scientific and nutritional literature [1] which documents their properties as a nutritive supplement and as medicinal compounds which are of potential application in a number of therapeutic areas in biomedicine [3][4][5][6][7][8][9][10][11][12].…”