Thiol-reactive natural antimicrobials and high pressure treatment synergistically enhance bacterial inactivation

摘要

Bacterial inactivation by high pressure (HP) treatment can be strongly enhanced in the presence of antimicrobial compounds, but the mechanism of this synergy is poorly understood. In the present study, screening of thirteen natural antimicrobial compounds (NACs) led to the identification of six NACs that exhibited synergy with HP treatment against eight Gram-negative and two Gram-positive bacteria. The strongest synergy was found with alpha,beta-unsaturated aldehydes (t-cinnamaldehyde, t-2-hexenal, dimethylfumarate), isothiocyanates (allyl isothiocyanate, sulforaphane) and other electrophilic compounds (reuterin). The antibacterial activity of these compounds and their synergistic interaction with HP was linked to thiol reactivity based on (1) their reaction with cysteine in vitro, (2) their reduced minimal inhibitory concentration in an Escherichia coli gshA mutant which is defective in glutathione synthesis, and (3) the loss of synergy with HP in the presence of excess cysteine. These novel insights in the mechanisms leading to synergy will support the development of more effective hurdle technology applications of HP treatment and natural antimicrobials.