Sub-lethal doses of photodynamic therapy affect biofilm formation ability and metabolic activity of Enterococcus faecalis.
BACKGROUND
During photodynamic therapy (PDT) in the treatment of a primary endodontic infection, it is extremely likely that microorganisms would be exposed to sub-lethal doses of PDT (sPDT). Although sPDT cannot kill microorganisms, it can considerably influence microbial virulence. This study was conducted to characterize the effect of sPDT using toluidine blue O (TBO), methylene blue (MB), and indocyanine green (ICG) on biofilm formation ability and metabolic activity of Enterococcus faecalis.


METHODS
The antimetabolic and antibiofilm potential of ICG-, TBO-, and MB-sPDT against E. faecalis was analyzed at sub-lethal doses (1/2-1/64 minimum inhibitory concentration) using the XTT reduction assay, crystal violet assay, and scanning electron microscopy.


RESULTS
Higher doses of sPDT adversely affected biofilm formation ability and metabolic activity. ICG-, TBO-, and MB-PDT at a maximum sub-lethal dose markedly reduced the formation of biofilm up to 42.8%, 22.6%, and 19.5%, respectively. ICG-, TBO-, and MB-sPDT showed a marked reduction in bacterial metabolic activity by 98%, 94%, and 82%, respectively. ICG-PDT showed a stronger inhibitory effect on biofilm formation in E. faecalis than MB- and TBO-PDT at sub-lethal levels. Interestingly, a gradual increase in metabolic activity and biofilm formation upon exposure to a lower dose of test sPDT were observed.


CONCLUSIONS
sPDT showed dual effect on biofilm formation ability and metabolic activity of E. faecalis. High doses revealed antimetabolic and antibiofilm potential activity, whereas lower doses had conflicting results. Hence, when PDT is prescribed in clinical settings, the dose of PDT used in vivo should be taken into consideration.
Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
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Pourhajibagher
Laser Research Center of Dentistry, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran.
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Chiniforush
Dental biomaterials Department, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
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S
Shahabi
Private practice, Tehran, Iran.
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R
Ghorbanzadeh
Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran; Laser Research Center of Dentistry, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran. Electronic address: abahador@sina.tums.ac.ir.
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A
Bahador
D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development* / Q000528:radiation effects; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D013293:Enterococcus faecalis / Q000187:drug effects* / Q000378:metabolism* / Q000528:radiation effects; D007208:Indocyanine Green / Q000008:administration & dosage; D008027:Light; D008751:Methylene Blue / Q000008:administration & dosage; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000008:administration & dosage*; D018915:Root Canal Preparation / Q000379:methods; D014048:Tolonium Chloride / Q000008:administration & dosage
D017319:Photosensitizing Agents; D014048:Tolonium Chloride; D007208:Indocyanine Green; D008751:Methylene Blue
Biofilm; Enterococcus faecalis; Indocyanine green; Methylene blue; Photodynamic therapy; Root canal; Toluidine blue O