Time-dependent antimicrobial effect of photodynamic therapy with TONS 504 on Pseudomonas aeruginosa
Pseudomonas aeruginosa (P. aeruginosa) is a major cause of infectious keratitis, which itself is a major cause of blindness worldwide. We have now evaluated the time-dependent effectiveness of photodynamic antimicrobial chemotherapy (PACT) with the chlorin derivative TONS 504 and a light-emitting diode (LED) on P. aeruginosa in vitro. PACT with TONS 504 (10 mg/L) and irradiation (30 J/m2) by an LED device that delivers light centered on a wavelength of 660 nm was applied to 1 × 106 colony-forming units of P. aeruginosa in liquid medium. The bacteria were then cultured at 37 °C for various times before assay of viability by determination of colony formation on agar plates. The effect of a second irradiation at 3 h after the initial LED exposure was also examined. Bacterial growth was markedly inhibited between 3 and 9 h after PACT with TONS 504, with the maximal effect being apparent at 3 h. Furthermore, a second exposure to LED irradiation at 3 h after the first treatment enhanced the inhibitory effect on bacterial growth. PACT with TONS 504 thus inhibited the growth of P. aeruginosa in a time-dependent manner, and an additional irradiation exposure applied 3 h after the first LED treatment greatly increased the effectiveness of PACT. This antibacterial system thus warrants further evaluation with regard to its potential effectiveness for the treatment of infectious keratitis.
KeywordsPhotodynamic antimicrobial chemotherapy (PACT) Pseudomonas aeruginosa Chlorin derivative TONS 504 Light-emitting diode (LED) Infectious keratitis
We thank Isao Sakata (Porphyrin Laboratory, Okayama, Japan) for providing information on TONS 504 as well as Akira Ichikawa (CCS, Kyoto, Japan) for building the LED device according to our design.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All experimental protocols were approved by the Hiroshima University Animal Experiment Committee, and were in keeping with the basic guidelines of Hiroshima University regarding animal experiments (Approval number: A15–76).
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