Inhibition of bacterial growth and biofilm production by constituents from Hypericum spp.

Biofilm embedded bacterial pathogens such as Staphylococcus spp., Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii are difficult to eradicate and are major sources of bacterial infections. New drugs are needed to combat these pathogens. Hypericum is a plant genus that contains species known to have antimicrobial properties. However, the specific constituents responsible for the antimicrobial properties are not entirely known, nor have most compounds been tested as inhibitors of biofilm development. The investigation presented here tested seven secondary metabolites isolated from the species Hypericum densiflorum, Hypericum ellipticum, Hypericum prolificum, and Hypericum punctatum as inhibitors of bacterial growth and biofilm production. Assays were conducted against Staphylococcus epidermidis, Staphylococcus aureus, clinical methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Escherichia coli, and Acinetobacter baumannii. Five of the seven compounds demonstrated growth inhibition against the Gram-positive bacteria with minimum inhibitory concentrations (MIC) ranging from 1.95 µg/mL to 7.81 µg/mL. Four of the secondary metabolites inhibited biofilm production by certain Gram-positive strains at sub-MIC concentrations.

Prenylated benzophenone derivatives from Clusia havetiodes var. stenocarpa.

Extracts of the fruit of Clusia havetiodes var. stenocarpa have yielded three new prenylated benzophenone derivatives, 28,29-epoxyplukenetione A (1), 33-hydroperoxyisoplukenetione C (2), and 15,16-dihydro-16-hydroperoxyplukenetione F (3), as well as four which have been previously described, plukenetiones C, F, and G and sampsonione G.

The Weber fraction versus perceived similarity.

The Weber fraction type of discrimination outcome means that stimuli of high magnitude are difficult to discriminate. Simultaneous and successive discriminations between two long (high magnitude) lines and also between two short (low magnitude) lines were carried out. Over-all performance on the successive discrimination between the two long lines was much poorer than on the three other discriminations. This discrimination also produced the poorest performance on different stimuli relative to same stimuli. The latter result should indicate that the two successive long lines were perceived as most similar. These and additional results support the conclusion that over-all discrimination performance and perceived similarity were consistently associated even though they were not consistently associated with length and time of occurrence (simultaneous versus successive). Nevertheless, the association of discrimination with perceived similarity has received minimal attention in the psychophysics area.