Combining antibiotics and photodynamic therapy to inactivate Staphylococcus aureus on skin

• Autor(a) principal: Branco, Tatiana Moura
• Data de Publicação: 2016
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/22361
• topic: Antibióticos; Terapia fotodinamica; Porfirinas

Staphylococcus aureus is a Gram-positive bacterium common in skin infections, but this bacterium can spread through the bloodstream and infect distant organs. To the treatment of this infections antibiotics are usually used, however, microorganisms have acquired the capacity to develop resistance against antimicrobial agents. Antimicrobial photodynamic therapy (aPDT) is being actively studied as a possible alternative to antibiotics to treat localized infections. This study was conducted to evaluate the antibacterial activity of aPDT for treatment of S. aureus infections on skin. The synergistic effect of aPDT and antibiotics (ampicillin, chloramphenicol, kanamycin, penicillin G and tetracycline) to inactivate S. aureus was also evaluated. To this purpose, a tetracationic porphyrin, the 5,10,15,20-tetrakis(1-methylpiridinium-4-yl)porphyrin tetra-iodide (Tetra-Py+-Me) was used to inactivate S. aureus in vitro using a buffer solution (PBS) and ex vivo, on pork skin artificially contamined with S. aureus. The results show an efficient inactivation of S. aureus in PBS using 5.0 μM of Tetra-Py+-Me during 180 min in the presence of a white light at an irradiance of 40 W m-2 (reduction of 8 log). When aPDT was done in the presence of ampicillin at 0.5 and 1.0 μg mL-1 (MIC dose 0.25 μg mL) in PBS a faster decrease (8 log) in total bacterial number was observed at 60 and 30 min, respectively. For the other antibiotics no increase in bacterial inactivation was observed. In ex vivo experiments a reduction of ~4 log of S. aureus after treatment with 50 μM of Tetra-Py+-Me under after 180 min. The efficiency of inactivation in the skin in the same conditions but in the presence of 5 μg mL-1 of ampicillin at 50 μM was significantly different of that obtained with PS in the absence of antibiotic with an inactivation of ~5.6 log. The results of this study showed that aPDT is an effective approache to control S. aureus infection in skin, inactivating the bacteria to the detection limit after three cycles of treatment. Moreover, the combination of aPDT with antibiotics can increase the efficacy of bacterial inactivation, allowing the reduction the treatment time for a quarter.