Effects of chitosan on the efficacy of methylene blue mediated photodynamic therapy against Gram-negative bacterial planktonic cells and biofilms
Date Issued
2011
Date
2011
Author(s)
Hong, Jia-Lin
Abstract
Biofilms are groups of microbes that attached to a surface. They can grow on indwell medical devices or human tissues, resulting in chronic or persistent infections. Because biofilms have stronger resistance to antibiotics than planktonic cells, those infections of biofilms are hard to treat. Photodynamic therapy (PDT) is an emerging method to treat microbial infections. So far, there is no strain resistant to PDT being observed. PDT is effective against Gram-positive planktonic cells and biofilms as well as drug-resistant strains. However, Gram-negative bacteria are more resistant to PDT. In this study, we used chitosan to enhance the efficacy of PDT. The results show that methylene blue-mediated PDT has a poor efficacy to Gram-negative bacteria, but it is more effective to planktonic cells treated with 0.0004% of chitosan for 10 minutes. Biofilms treated by 0.05% of chitosan for 90 minutes are also more sensitive to PDT. We observed that there is a threshold of methylene blue excitation level at 1 nmol/mL. If the excitation level of methylene blue is higher than the threshold, all the bacteria will be killed. After the treatment of chitosan, the amount of methylene blue binding to bacteria is increased, and the excitation level of methylene blue is higher. It implies that chitosan can enhance the binding between bacteria and methylene blue. The images taken by scanning electron microscope show bacteria aggregated after treatment of chitosan. Our result shows that chitosan have weak binding ability to methylene blue, it cannot explain the mechanism of chitosan enhancing PDT. However, the use of chitosan to enhance the efficacy of PDT may be a potent method.
Subjects
photodynamic therapy
biofilm
methylene blue
chitosan
Type
thesis
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