EFFECT OF COMBINED ANTIBIOTIC AND PHOTODYNAMIC TREATMENT ON VIABILITY OF BACTERIA

Non-controlled, excessive and inappropriate use of antibiotics against pathogenic bacteria has triggered bacterial resistance to antibiotics. An alternative to antibiotic treatment is photodynamic antimicrobial chemotherapy based on excitation of dyes called photosensitizers by visible light. This technique can be applied for treatment of bacterial infections, especially those caused by antibiotic-resistant strains of bacteria. No resistance of bacteria to photosensitizers has been reported to date. In the present study the effect of the photosensitizer Rose Bengal, alone or in combination with methicillin, on viability of Gram-positive Staphylococcus aureus was studied. Minimum inhibitory concentration (MIC) of methicillin was decreased 2-30 fold in the presence of sub-MIC concentrations of Rose Bengal. Hospital isolates of Methicillin Resistant Staphylococcus aureus (MRSA) strains were found to be sensitive to Rose Bengal although the MIC values of the latter were 2-16 times higher than the MIC of the methicillin sensitive Staphylococcus aureus strain (MSSA). Photodynamic inactivation of S. aureus by Rose Bengal opens prospects for developing an alternative to antibiotic treatment of bacterial infections.