Photodynamic antimicrobial chemotherapy action of phenothiazinium dyes in planktonic Candida albicans is increased in sodium dodecyl sulfate.

BACKGROUND

Photodynamic antimicrobial chemotherapy (PACT) is an important therapeutic platform for antimicrobial activity, especially due to the resistant strains, however, the physical-chemical properties of the photosensitizers may affect the final outcome. Recently, this research group showed that the control of aggregation potentiates the PACT action of Methylene Blue. In this study, the researchers investigated the PACT action of other phenothiazinium dyes (PDs), such as Azure A, Azure B (AB), and 1,9-dimethyl methylene blue (DMMB), and the effects of different mediums which modulate PD aggregation were studied.

METHODS

The C. albicans planktonic culture was treated with PDs at different concentrations (0-100.00 mg/L), both in the dark (5 min) and irradiated (640 ± 12 nm LED during 30 min, 2.60 mW/cm2). After the treatments, the diluted samples were grown on Sabouraud Dextrose Agar and maintained at 37 °C for 24 h. Later, one single concentration was defined and the inoculum was treated with the compounds in different media (water, phosphate buffer saline - PBS, physiological solution - 0.90 % NaCl, urea 1.00 mol/L, and sodium dodecyl sulfate 0.25 % - SDS), at 20.00 mg/L for AA and AB, and at 0.50 mg/L for DMMB. The cell uptake and the dimer to the monomer ratios were determined by spectrophotometry.

RESULTS

PACT with the PDs showed a reduction in the CFU/mL, with DMMB being the most effective due to the higher cell uptake within the series. When PACT was applied in the different mediums, the inactivation response was influenced by the medium. In water, the physiological solution, PBS, and urea showed no significant differences in relation to the control group. On the other hand, SDS potentiated the PACT action, and the inactivation of the microorganism was achieved with AB and DMMB.

CONCLUSIONS

In water, DMMB presented the highest PACT action within the PDs being studied, reaching a microorganism inactivation with a 1.00 mg/L solution, mainly due to its high cell uptake. SDS 0.25 % increased the PACT action of the PDs studied, mainly with DMMB and AB, and this may be used in formulations to develop antimicrobial treatments to be used in clinics.