Photodynamic inactivation of Staphylococcus aureus employing PSs derived from plants

GÁNDARA L; MAMONE L; VAINMAN M; ROSSETTI MV; DI VENOSA G; CALVO G; BATLLE A; BUZZOLA F; CASAS A

Lucerna

Congreso; Annual Assembly of the Swiss Society of Clinical Chemistry & International Congress of Porphyrins and Porphyrias & International Meeting of Porphyria Patients; 2013

Swiss Society of Clinical Chemistry

Proposed clinical fields of interest of antimicrobial Photodynamic Inactivation (PDI) include the treatment of chronic ulcers, infected burns, acne vulgaris, cutaneous leshmaniasis, and a variety of oral infections.  PDI has been employed in eradication of biofilms present in dental plaques, oral implants, prothesis and infected catheters. On the other hand, PDI employing cationic (PS) are particularly efficient in the treatment of S. aureus and S. epidermidis biofilms. Among the bacteria, Staphylococcus aureus is particularly clinically important since the emergency of resistance to antibiotics leads to the need of new alternative therapies. In a screening study, we have identified several plants with high photoactivity against bacteria. The aim of this work was to evaluate the ability of natural and synthetic PSs to photoinactivate S. aureus (SH100 strain and RN6390 strain, deficient in sigB factor and thus impaired in its ability to produce the antioxidant pigment Staphyloxanthyne). The radiation source was a set of two tungsten halogen lamps of about 23 mW/cm2. Unirradiated and irradiated cells were serially diluted with PBS and each dilution was plated on a solid growth medium. PDI of S. aureus RN6390 employing Solanum verbascifoliium flower extract (0.5 mg/ml) and Cissus verticillata root (0.5 mg/ml); induce an impairment of 6 logs decrease of CFU, Combretum fruticosum leaf (0.5 mg/ml) provoked 1 log decrease, whereas Scutia buxifolia leaf (0,01mg/ml) induced 2 logs decrease. Suspensions exposed to Toluidine blue-PDI (synthetic PS) induced 7 logs decrease employing 5 µM. Mean ± SD were as follows: Control:  1.3x108 ± 8.7x107 CFU/ml vs  Cissus verticillata 0.5 mg/ml: 7.7x102 ± 9.2x102; Solanumverbascifollium 0.5 mg/ml: 1.9 x102 ± 2.1x102; Combretum fruticosum 0.005 mg/ml: 4.3x107 ± 5.4 107; Scutia buxifolia 0.01 mg/ml: 7.7x106 ± 1.0x107 and Toluidine blue 5 µM:  9.08x101 ± 2.01x102 (p< 0.01, Mann-Whitney test). RN6911 strain was more resistant to PDI employing all the PSs as compared to RN6390. The most relevant conclusion is that S. aureus can be photoinactivated employing both natural and synthetic PSs. We are carrying out studies to photoinactivate biofilms.