Antimicrobial properties of natural coniferous rosin in the European Pharmacopoeia challenge test.

Rosins (resins) are natural products of the coniferous trees. Purified rosin from the trunk of Norway spruce (Picea abies) is antibacterial against the gram-positive bacteria, but not against the gram-negative bacteria in agar plate diffusion test. In this study, we examined the antimicrobial properties of the coniferous rosin against bacteria and yeasts using the European Pharmacopoeia (EP) challenge test. The microbes tested were Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Candida albicans. To prepare challenge media, purified rosin was mixed with a biologically inert salve in varying concentrations. The microbes were inoculated (5 × 10(5) microbes (bacteria) or 5 × 10(4) microbes (yeast, C.albicans)) into 10 g of the rosin-containing challenge medium for 14 days at maximum. Samples were taken from the media for re-cultivation of the microbes at time intervals of 1 h, 24 h, 4, 7, and 14 days. The microbicidal efficacy of the challenge media was estimated by reduction of the number of the colony forming units (CFU) of microbes in the test samples. A reduction of more than 10(3) CFU for bacteria and 10(2) CFU for fungi in 7 days was considered to indicate a significant microbicidal action. Pure rosin was antimicrobial within 24 h against all microbes tested. The 0.5% rosin-salve medium (w/w) did not differ in microbicidal effects from the rosin-free salve medium (control). A raise of the rosin concentration resulted in increase of the microbicidal effect of the rosin-salve medium against all micro-organisms tested. Rosin concentration of 10% (w/w) in the medium significantly reduced the colonization of S. aureus (including MRSA) within 24 h and significantly reduced the colonization of all other micro-organisms within 4 days. Rosin is strongly microbicidal against a wide range of microbes, against both gram-positive and gram-negative bacteria, and against C. albicans, in the EP challenge test. The minimum concentration of rosin is 10% (w/w) to prevent the preservation of the microbes in the rosin-salve media.