Photodynamic inactivation of Gram-positive bacteria employing natural resources

MAMONE L; GANDARA L; DI VENOSA G; VAINMAN M; SCHICKINGER S; ROSSETTI MV; BATLLE A; BUZZOLA F; CASAS A

Lucerna

Congreso; International Congress of Porphyrins and Porphyrias; 2013

Swiss Society of Clinical Chemistry

The aim of our work is to investigate a collection of plant extracts from Argentina as a source of new natural photosensitizers to be used in Photodynamic Inactivation (PDI) of bacteria. A collection of Argentinian plants were screened for toxicity upon the Gram-positive species Staphylococcus epidermidis. Three extracts turned out to be highly photoactive: Solanum verbascifolium, Tecoma stans and Cissus verticillata employed at non toxic concentrations induced 4, 2 and 3logs decrease in cell survival of S. epidermidis respectively, upon exposure to a light dose af 55 J/cm2. Positive controls of Chlorin e6 and Toluidine blue provoked a reduction of aproximately 6 logs under these conditions. Suspensions of S. epidermidis incubated with S. verbascifolium extract revealed that fluorescence quickly binds to the bacteria membrane. S. verbascifolium photochemistry was further studied. The PDI reaction was dependent mainly on singlet oxygen and hydroxyl radicals to a lesser extent, through the involvement of type II and I reactions respectively. Photodegradation employing artificial light revealed that the active principleof the extract was not particularly photolabile, and its product of degradation is still photoactive after 120 min of light exposure. Even considering the sunlight spectrum and high fluence during summer in South America, it is noticeable that S. verbascifolium -PDI is more efficient under sunlight, inducing decrease of 4 logs CFUs of S. epidermidis exposed 120 min, whereas artificial light induced 6 logs decrease. Even the response of PS to sunlight is particular for each entity, and the advantage of using solar light is the exploitation of the entire absorption spectra of each photosensitizing molecule. The balance between oxidant and antioxidant compounds is very likely to be maskingor unmasking potencial PS in the extracts, but we have demonstrated that employing the crude extract, the level of photoactivity is of the same extent of some artificial PS upon exposure to sunlight, demonstrating that natural resources can be employed for PDI of bacteria.