Effects of demethylfruticulin A and fruticulin A from Salvia corrugata Vahl. (Lamiaceae) on biofilm production in vitro by multiresistant strains of Staphylococcus aureus and S. epidermidis.

In this study we assessed whether demethyl fruticulin A (dfA) and fruticulin A (fA) two quinones that represent the mayor diterpenoid components of the exudate produced by the aerial parts of Salvia corrugata Vahl., were able to inhibit the synthesis of biofilm produced in vitro by multiresistant S. aureus and S. epidermidis. Five clinical strains of S. aureus -3 methicillin resistant (MRSA) and 2 methicillin susceptible (MSSA) - and five clinical strains of S. epidermidis (4 MRSE and 1 MSSE) were used. FA decreased by at least twofold the hydrophobic properties of S. aureus cell membrane, evaluated by standard methods [1]. Biofilm formation on polystyrene plates was quantified spectrophotometrically by established methodologies [2] and was also confirmed by the Congo red plate assay [3]. DfA and fA were more effective against S. aureus strains (>70% effect at sub-MIC concentrations) than against S. epidermidis in inhibiting slime synthesis. Moreover, the two compounds were shown to posses chelating activity on divalent and trivalent metal cations by the batochromic shifts of their UV spectra in presence of Al3+ and Mg2+ ions [4, 5]. Our results indicate that fA and dfA interaction with bacteria could be very complex, being possibly species-specific, and could depend not only on EPS synthesis inhibition but also on their chelating activity and on changes in the microorganism surface, including cell hydrophobicity. References: 1. Rosenberg, M. Bacterial adherence to hydrocarbons: A useful technique for studying cell surface hydrophobicity. FEMS Microbiol. Lett.1984, 22, 289-295). 2. Cramton SE, Gerke C, Götz F. In vitro methods to study staphylococcal biofilm formation. Methods Enzymol. 2001;336:239-55. 3. Freeman DJ, Falkiner FR, Keane CT. New method for detecting slime production by coagulase negative staphylococci. J Clin Pathol. 1989 Aug;42(8):872-4. 4. Mabry T.J., Markham K.R., Thomas M.B. 1970. The Systematic identification of Flavonoids. Springer, Berlin, 35-39. 5. European Pharmacopoeia. Fourth Edition. Council of Europe, Strasbourg. 1227.