Antibacterial activity of natural anthraquinones

COMINI L.R.; HEUMANN V.; PAÉZ P.L.; ALBESA I.; NÚÑEZ MONTOYA S.C.; CABRERA J.L.

Buenos Aires. Argentina

Congreso; AAPS Pharm Sci Tech; 2010

RICIFA

Introduction and objectives Substances with photosensitizing characteristics have become particularly important in the field of pharmacology due to their potential applications (1). In relation to this, research oriented towards photodynamic antimicrobial chemotherapy is in progress with promising results. This therapeutic treatment consists in the application of ultraviolet or visible radiation (UV-Vis) on infected tissue, which is previously associated to the photosensitizer (PS), which is activated by light in order to produce reactive oxygen species (superoxide anion radical and/or singlet molecular oxygen). These species act on microorganisms, generating microbial inactivation (2). Previously, we have demonstrated that three majority anthraquinones (AQs): rubiadin, soranjidiol and rubiadin 1-methyl ether, isolated from stems and leaves of Heterophyllaea pustulata, showed photosensitizing properties by generation of superoxide anion radical and/or singlet molecular oxygen under irradiation conditions (3). On the other hand, in previous microbiological studies we have established that two of the tested AQs (rubiadin and soranjidiol), have in vitro photodynamic antimicrobial activity against Gram (+) bacteria (Staphylococcus aureus ATCC 25923) (4). In the present work, the objective was to evaluate the antibacterial activity of these AQs against another microorganism that belong to Gram (+) genus: Staphylococcus. Materials and methods Measurement of the Minimum Inhibitory Concentration (MIC) for each AQ was carried out in Staphylococcus epidermidis ATCC 12228, by means of broth macrodilution method, in accordance with international standards of the Clinical and Laboratory Standards Institute (CLSI) (5). Results The results of dilution in broth were satisfactory for the three assayed AQs. Thus, S. epidermidis showed susceptibility with a MIC of 125 mg/mL for rubiadin 1-methyl ether, and 250 mg/mL for rubiadin and soranjidiol. Discussion Previous results showed that rubiadin and soranjidiol had a MIC for S. aureus between 32-64 µg/mL, and the MIC for rubiadin 1-methyl ether was higher than 250 µg/mL (4). However, this methylated derivative exhibited a higher antimicrobial activity against S. epidermidis than rubiadin and soranjidol. Therefore, these results are remarkably promising because each one of these AQs derivatives has demonstrated to possess a selective effect against one or the other of the two assayed species of Staphylococcus. Thus, this encourages us to carry out further test in order to study in depth the photodynamic antimicrobial activity of these metabolites.