Efficacy of photodynamic antimicrobial chemotherapy on gram negative bacteria

Abstract

Purpose: To evaluate the effectiveness of photodynamic antimicrobial chemotherapy (PACT) on gram negative bacteria.

Methods: A derivative porphyrin (TONS504; Porphyrin Lab., Okayama) with light emitting diode (LED) exposure by the LED device (CCS Inc., Kyoto) was applied in vitro onto 10⁷ colony forming unit of Pseudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli) and Serratia marcescens (S. marcescens) with an additional agent of ethylene diamine tetra acetic acid (EDTA). The LED lighting device which can supply a single wavelength (660 nm) was applied with 10, 20 and 30 J/cm². After applying TONS504 with various concentrations (0.5 to 20μg/mL) mixed with 0.05M of EDTA and followed by LED exposure, bacterial suspensions on 24 wells plate were incubated overnight in 37°C. The growth activity was evaluated by cultured on standard agar, and confirmed by counting bacterial colony formation after 30 minutes and 24 hours incubation.

Results: TONS504-PACT showed a dose dependent inhibition on bacterial growth of gram negative bacteria. After 30 minutes LED exposure, there is no complete inhibitory effect on bacterial growth from this treatment. The completely inhibitory effect on bacterial growth was founded after 24 hours incubation with the concentration of TONS504 from 10μg/mL with 10J/cm², and from 1μg/mL with 20 and 30J/cm² of LED exposure. However, TONS504 in the concentration between 0.5 to 20μg/mL without LED exposure had no inhibition on gram negative bacteria.

Conclusions: TONS504-PACT had a bactericidal effect in vitro on gram negative bacteria with the presence of EDTA.

Keywords: 480 cornea: basic science • 422 antibiotics/antifungals/antiparasitics • 573 keratitis