Effect of Photodynamic Antimicrobial Chemotherapy Combined with Antibiotic Treatment on Antibiotic Resistant Bacteria

Yana Ilizirov, Ariel University, Ariel, Israel
Marina Nisnevitch, Ariel University, Ariel, Israel

Resistance of bacteria to antibiotics is a well-known phenomenon and rapidly growing caused by uncontrolled, excessive and inappropriate use of antibiotics. Bacterial cells develop resistance to the antibiotics by natural selection after repeated exposure to certain antibiotics. Recently, an alternative to antibiotic treatment based on excitation of photosensitizers by visible light was developed. This treatment was called photodynamic antimicrobial chemotherapy (PACT). PACT is based on a combination of photosensitizers and visible or ultraviolet light in order to provide a phototoxic response, usually via oxidative damage. Currently, the major application of PACT lies in disinfection of blood products, particularly for viral inactivation, although clinical protocols have being developed for the treatment of oral and skin infections and some types of cancer. The PACT technique has been shown to be effective in vitro against bacteria (including drug-resistant strains), yeasts, viruses and parasites. In this study the effect of the photosensitizer Rose Bengal on hospital isolates of Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) was examined when Rose Bengal was applied alone or in a combination with methicillin. Our results show that all the MRSA strains were sensitive to Rose Bengal. In the presence of sub-MIC Rose Bengal concentrations, the MIC of methicillin dropped significantly for six MRSA strains. However, in the case of three other MRSA strains the addition of Rose Bengal did not restore the sensitivity of bacteria to methicillin. Photodynamic inactivation of S. aureus by Rose Bengal may become an alternative to antibiotic treatment of bacterial infections.