Neutral red monobrominated as photoantimicrobial agent against Staphylococcus aureus

URRUTIA, MARÍA NOEL; ALOVERO, FABIANA L.; ORTIZ, CRISTINA

Congreso; 3rd International Meeting on Pharmaceutical / 3ª Reunión Internacional de Ciencias Farmacéuticas-; 2014

UNIVERSIDAD NACIONAL DE CORDOBA Y UNIVERSIDAD NACIONAL DE ROSARIO

Photodynamic Antimicrobial Chemotherapy was proposed as an alternative treatment for localized infections in response to the worldwide problem of resistance because of its efficacy and to be less likely to induce resistance. Neutral Red monobrominated (NRBr) is a new azine compound synthesized in our laboratory derivated from Neutral Red (NR). In a previous work, NRBr showed physicochemical and photophysical properties appropriate for potential use as a photosensitizer (PS). In this study, the photoantimicrobial effect was evaluated in S.aureus. Simultaneously, NR was assayed since reports on effects against bacteria are limited. S.aureus ATCC 25923 and methicillin- and fluoroquinolone-resistant S.aureus isolate (MRSA61) were used to determine effect of PS concentration (5-200 µM) and visible irradiation time (15, 30, 60 min). Aliquots serially diluted in phosphate buffered saline were subcultured on Müller-Hinton agar and incubated 18-24 h at 37°C for survival account. Three independent experiments were performed and data averaged. Means were compared by a two-tailed unpaired Student?s t test. Both PS were not toxic for S.aureus in the dark up to 200 μM. NRBr was significantly more phototoxic than NR toward these bacteria, displaying dependent effect of both time-exposure and concentration. NRBr 50 µM reduced >4 log survival of S.aureus ATCC 25923 after 30 min light exposure. No viable bacteria were detected after 60 min throughout the concentrations range. Conversely, NR was unable to complete photoinactivation under assessed conditions. The greatest effect (~3.2 log decrease) was observed with 50 µM after 60 min, without significant changes by increasing the concentration. NRBr was slightly less phototoxic against MRSA61; 25 and 50 µM led to 3.3 and 3.7 log killing, respectively, for multidrug-resistant isolate while 4.2 and 5.03 log were observed against sensitive strain. Significant increases in photoantimicrobial action of NRBr compared to NR, suggesting that new azine derivative could be a promising PS for use in photodynamic inactivation of S.aureus.