Antibacterial and antifungal activity of Avarone and Avarol

The sesquiterpenoid hydroquinone and quinone, Avarol and Avarone, were previously found to be potent antitumor agents (Müller et al., 1984). In the present study it is reported that in aqueous solution (pH 7.2), in the presence of dimethylsulfoxide, Avarol is converted to Avarone. Avarone and to a smaller extent also Avarol were active against a variety of grampositive bacterial species. The highest activity was determined for Streptococcus pneumoniae and Erysipelothrix rhusiopathiae (MIC 0.781 mg/l). The antibacterial activity can be augmented 2 to 4-fold by lowering the pH in the culture medium from 7.0 to 6.0. The efficiency of Avarone and Avarol was abolished in the presence of serum. No antibacterial activity was determined in gramnegative bacterial species. In addition, Avarol and to a smaller extent also Avarone displayed an antifungal activity on Trichophyton species and Microsporum canis (MIC: 15.6-62.5 mg/l), while Avarone and not Avarol was active on Aspergillus niger, no activity was found against Candida species. These data indicate that the antitumor agents Avarol/Avarone display also antibacterial- and antifungal activities against a limited range of microorganisms.