Photodynamic inactivation of Staphylococcus aureus and Escherichia coli biofilms by malachite green and phenothiazine dyes: an in vitro study.
OBJECTIVE
The organization of biofilms in the oral cavity gives them added resistance to antimicrobial agents. The action of phenothiazinic photosensitizers on oral biofilms has already been reported. However, the action of the malachite green photosensitizer upon biofilm-organized microorganisms has not been described. The objective of the present work was to compare the action of malachite green with the phenothiazinic photosensitizers (methylene blue and toluidine blue) on Staphylococcus aureus and Escherichia coli biofilms.


METHODS
The biofilms were grown on sample pieces of acrylic resin and subjected to photodynamic therapy using a 660-nm diode laser and photosensitizer concentrations ranging from 37.5 to 3000 μM. After photodynamic therapy, cells from the biofilms were dispersed in a homogenizer and cultured in Brain Heart Infusion broth for quantification of colony-forming units per experimental protocol. For each tested microorganism, two control groups were maintained: one exposed to the laser radiation without the photosensitizer (L+PS-) and other treated with the photosensitizer without exposure to the red laser light (L-PS+). The results were subjected to descriptive statistical analysis.


RESULTS
The best results for S. aureus and E. coli biofilms were obtained with photosensitizer concentrations of approximately 300 μM methylene blue, with microbial reductions of 0.8-1.0 log(10); 150 μM toluidine blue, with microbial reductions of 0.9-1.0 log(10); and 3000 μM malachite green, with microbial reductions of 1.6-4.0 log(10).


CONCLUSIONS
Greater microbial reduction was achieved with the malachite green photosensitizer when used at higher concentrations than those employed for the phenothiazinic dyes.
Department of Biosciences and Oral Diagnosis, Laboratory of Microbiology, School of Dentistry of São José dos Campos, UNESP - Univ Estadual Paulista, Francisco José Longo 777, 12245-000 São José dos Campos, SP, Brazil. simonefurgeri@gmail.com
Simone Furgeri Godinho
SF
Vilela
Juliana Campos
JC
Junqueira
Junia Oliveira
JO
Barbosa
Marta
M
Majewski
Egberto
E
Munin
Antonio Olavo Cardoso
AO
Jorge
D018441:Biofilms / Q000187:drug effects*; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000187:drug effects* / Q000528:radiation effects; D066298:In Vitro Techniques; D008751:Methylene Blue / Q000494:pharmacology*; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D012394:Rosaniline Dyes / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000528:radiation effects; D014048:Tolonium Chloride / Q000494:pharmacology*
D017319:Photosensitizing Agents; D012394:Rosaniline Dyes; C005095:malachite green; D014048:Tolonium Chloride; D008751:Methylene Blue