Diverse outcomes of Photodynamic Antimicrobial Chemotherapy on five Enterococcus faecalis strains

• Photogem alone was distinctly toxic to planktonic cells of Enterococcus faecalis.
• Photogem-mediated PACT was effective against biofilms of all E. faecalis strains.
• The efficacy of PACT on E. faecalis biofilms was strain-dependent.
• Clinical outcomes of PACT on E. faecalis probably vary among different patients.

SummaryObjectivesIn the present study, the effectiveness of Photodynamic Antimicrobial Chemotherapy (PACT) was evaluated on planktonic cells and biofilms of five Enterococcus faecalis clinical isolates.MethodsPlanktonic cells and biofilms of E. faecalis E2, E3, ER3/2s, OS16 and AA-OR34 were grown in SDMY medium plus 0.4% glucose. Approximately 5.0 × 107 CFU planktonic cells and 24 h biofilms were subjected to PACT using the combination of Light Emitting Diodes (LEDs, Biotable®) and Photogem®. The metabolic activity of bacterial cells was evaluated by a resazurin assay. Biomass values of the biofilms were determined by a crystal violet assay.ResultsCompared to the water-treated control group, gradual increases of light energy led to greater reduction of metabolic activity of planktonic cells and biofilms of E. faecalis when the combination of LEDs and Photogem® was applied. Photogem® alone significantly reduced the metabolic activity of planktonic cells, whereas LEDs or Photogem® alone did not result in biofilm viability changes. PACT yielded similar antimicrobial outcomes on planktonic cells of all tested E. faecalis strains, whereas biofilms of E. faecalis E3, ER3/2s and OS16 were more resistant to PACT than biofilms of E. faecalis E2 and AA-OR34.ConclusionsThe efficacy of PACT on E. faecalis biofilms was strain dependent. PACT demonstrated its potential as an adjuvant antimicrobial treatment by killing of E. faecalis planktonic and biofilm cells.