Contribution of reactive oxygen species to (+)-catechin-mediated bacterial lethality.

The contribution of reactive oxygen species to (+)-catechin-mediated bacterial lethality was investigated. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentration (MBC) of (+)-catechin against E. coli, P. aeruginosa and S. aureus were investigated using 96-well microtitre plate. MIC and MBC of (+)-catechin against E. coli, P. aeruginosa and S. aureus are 600 and 700; 600 and 800; 600 and 800 µg/mL respectively. The optical densities and colony forming units of (+)-catechin-treated bacteria decreased. (+)-Catechin (4× MIC) significantly increased the superoxide anion content of E. coli, P. aeruginosa and S. aureus compared to DMSO. Superoxide dismutase and catalase in (+)-catechin treated E. coli, P. aeruginosa and S. aureus increased significantly. Conversely, level of reduced glutathione in (+)-catechin-treated E. coli, P. aeruginosa and S. aureus decreased significantly while glutathione disulfide increased significantly. Furthermore, malondialdehyde and fragmented DNA increased significantly following exposure to (+)-catechin. From the above findings, (+)-catechin enhanced the generation of reactive oxygen species (superoxide anion radical and hydroxyl radical) in E. coli, P. aeruginosa and S. aureus, possibly by autoxidation, Fenton chemistry and inhibiting electron transport chain resulting into lipid peroxidation and DNA fragmentation and consequentially bacterial cell death.

Redox and respiratory chain related alterations in the lophirones B and C-mediated bacterial lethality.

The influence of chalcone dimers, lophirones B and C on redox status and respiratory chain activity of Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa was investigated. Minimum inhibitory concentrations (MIC) of lophirones B and C against E. coli, P. aeruginosa and S. aureus are 200-; 100-; 200- and 150-µg/mL respectively. Similarly, the minimum bactericidal concentrations (MBC) of lophirones B and C are 250; 200; 300 and 200-µg/mL respectively. The optical densities and colony forming units of lophirones B and C-treated bacteria decreased in time-dependent manner. Superoxide anion content of E. coli, P. aeruginosa and S. aureus exposed to lophirones B and C (4× MIC) increased significantly. Superoxide dismutase and catalase in the chalcone dimers-treated bacteria increased significantly. Conversely, reduced glutathione in lophirones B and C-treated bacteria decrease significantly with corresponding increase in glutathione disulfide. Furthermore, malondialdehyde and fragmented DNA increased significantly following exposure to the chalcone dimers. The respiratory complex I and II decreased significantly in the chalcone dimers-treated bacteria. From the findings, lophirones B and C altered intracellular redox status via enhanced oxidant generation possibly by autoxidation, Fenton chemistry and inhibiting electron transport chain resulting to lipid peroxidation and DNA fragmentation and consequentially bacterial cell death.