Photodynamic inactivation of multidrug-resistant bacteria mediated

Due mainly to the extensive use of antibiotics, the spread of drug-resistant bacteria is one of the most worrying threats to public health. One strategy can be used to overcome potential shortcomings might be the inactivation of these organisms by photodynamic therapy. In this study, we have investigated whether multidrug-resistant wound-associated organisms (methicillin-resistant Staphylococcus aureus, methicillin-resistant Staphylococcus epidermidis and ESBL-producing Escherichia coli) are sensitive to lethal photosensitization using the dye methylene blue (MB) coupled with laser light of 660 nm.

Effect of photosensitizer concentration (25, 50, 100 µg/ml) and laser light dose (27.3, 54.6 and 109.2 J/cm2) on lethal photosensitization was investigated.

All species were susceptible to kill by photodynamic inactivation. The bactericidal effect was not dependent on the concentration of methylene blue; but it was dependent on the light dose. Methylene blue photosensitization using red laser light (109.2 J cm-2) was able to achieve reductions of 99.03% and 98.95% in the viable counts of S. aureus and S. epidermidis (using starting concentrations of 104–105 CFU ml-1). Kills of 92.23% were obtained for E. coli (initial concentration 104–105 CFU ml-1) photosensitized by the red light (109.2 J cm-2).

These findings imply that methylene blue in combination with red light may be an effective means of eradicating multidrug-resistant bacteria from wounds.