Green-leaf-derived C6-aroma compounds with potent antibacterial action that act on both gram-negative and gram-positive bacteria

All eight C6-aliphatic alcohol and aldehyde compounds in naturally occurring green leaves showed bacteriostatic effects against Staphylococcus aureus IFO 12732, methicillin-resistant S. aureus, Escherichia coli IFO 3301, E coli O157:H7 and Salmonella enteritidis, with bacteriostatic activities of less than 12.5 mug mL(-1). In this study, the susceptibility of Gram-positive bacteria tested was, observed to be greater than that of Gram-negative bacteria. The bactericidal action of the aldehyde compounds was found to be much stronger than that of the alcohol compounds under both liquid and gaseous conditions. The Most effective compound was (3E)-hexenal at concentrations of 0.1, and 1 mug mL(-1), which killed 2.1 x 10(5) cfu mL(-1) of S. aureus IFO 12732 and 1.4 x 10(5) cfu mL(-1) of E coli IFO 3301, respectively, by direct contact with the compound. Lethality of (3E)-hexenal against S. aureus IFO 12732 and E coli IFO 3301 was also observed as a result of gaseous contact at concentrations of 3 and 30 mug mL-1, respectively. The bactericidal effects of 30 mug mL(-1) (3E)-hexenal were thoroughly maintained throughout periods of 2 days and 1 day against S. aureus IFO. 12732. and E. coli IFO 3301, respectively, by a complex formation with alpha-cyclodextrin.