Neutral red monobrominated as photoantimicrobial agent against Staphylococcus 1 aureus 2

MARÍA N. URRUTIA , FABIANA ALOVERO Y CRISTINA S. ORTIZ

Córdoba

Congreso; 3raReunión Internacional de Ciencias Farmacéuticas (RICiFA; 2014

Neutral red monobrominated as photoantimicrobial agent against Staphylococcus 1 aureus 2 3 Keywords: Neutral Red, Photosensitizer, Photodynamic Antimicrobial Chemotherapy 4 5 Photodynamic Antimicrobial Chemotherapy was proposed as an alternative treatment 6 for localized infections in response to the worldwide problem of resistance because of 7 its efficacy and to be less likely to induce resistance. Neutral Red monobrominated 8 (NRBr) is a new azine compound synthesized in our laboratory derivated from Neutral 9 Red (NR). In a previous work, NRBr showed physicochemical and photophysical 10 properties appropriate for potencial use as a photosensitizer (PS). In this study, the 11 photoantimicrobial effect was evaluated in S.aureus. Simultaneously, NR was assayed 12 since reports on effects against bacteria are limited. 13 S.aureus ATCC 25923 and methicillin- and fluoroquinolone-resistant S.aureus isolate 14 (MRSA61) were used to determine effect of PS concentration (5-200 μM) and visible 15 irradiation time (15,30,60 min). Aliquots serially diluted in phosphate buffered saline 16 were subcultured on Müller-Hinton agar and incubated 18-24 h at 37°C for survival 17 account. Three independent experiments were performed and data averaged. Means 18 were compared by a two-tailed unpaired Student?s t test. 19 Both PS were not toxic for S.aureus in the dark up to 200 μM. NRBr was significantly 20 more phototoxic than NR toward these bacteria, displaying dependent effect of both 21 time-exposure and concentration. NRBr 50 μM reduced >4 log survival of S.aureus 22 ATCC 25923 after 30 min light exposure. No viable bacteria were detected after 60 min 23 throughout the concentrations range. 24 Conversely, NR was unable to complete photoinactivation under assessed conditions. 25 The greatest effect (~3.2 log decrease) was observed with 50 μM after 60 min, without 26 significant changes by increasing the concentration. 27 NRBr was slightly less phototoxic against MRSA61; 25 and 50 μM led to 3.3 and 3.7 28 log killing, respectively, for multidrug-resistant isolate while 4.2 and 5.03 log were 29 observed against sensitive strain. 30 Significant increases in photoantimicrobial action of NRBr compared to NR, suggesting 31 that new azine derivative could be a promising PS for use in photodynamic inactivation 32 of S.Neutral red monobrominated as photoantimicrobial agent against Staphylococcus 1 aureus 2 3 Keywords: Neutral Red, Photosensitizer, Photodynamic Antimicrobial Chemotherapy 4 5 Photodynamic Antimicrobial Chemotherapy was proposed as an alternative treatment 6 for localized infections in response to the worldwide problem of resistance because of 7 its efficacy and to be less likely to induce resistance. Neutral Red monobrominated 8 (NRBr) is a new azine compound synthesized in our laboratory derivated from Neutral 9 Red (NR). In a previous work, NRBr showed physicochemical and photophysical 10 properties appropriate for potencial use as a photosensitizer (PS). In this study, the 11 photoantimicrobial effect was evaluated in S.aureus. Simultaneously, NR was assayed 12 since reports on effects against bacteria are limited. 13 S.aureus ATCC 25923 and methicillin- and fluoroquinolone-resistant S.aureus isolate 14 (MRSA61) were used to determine effect of PS concentration (5-200 μM) and visible 15 irradiation time (15,30,60 min). Aliquots serially diluted in phosphate buffered saline 16 were subcultured on Müller-Hinton agar and incubated 18-24 h at 37°C for survival 17 account. Three independent experiments were performed and data averaged. Means 18 were compared by a two-tailed unpaired Student?s t test. 19 Both PS were not toxic for S.aureus in the dark up to 200 μM. NRBr was significantly 20 more phototoxic than NR toward these bacteria, displaying dependent effect of both 21 time-exposure and concentration. NRBr 50 μM reduced >4 log survival of S.aureus 22 ATCC 25923 after 30 min light exposure. No viable bacteria were detected after 60 min 23 throughout the concentrations range. 24 Conversely, NR was unable to complete photoinactivation under assessed conditions. 25 The greatest effect (~3.2 log decrease) was observed with 50 μM after 60 min, without 26 significant changes by increasing the concentration. 27 NRBr was slightly less phototoxic against MRSA61; 25 and 50 μM led to 3.3 and 3.7 28 log killing, respectively, for multidrug-resistant isolate while 4.2 and 5.03 log were 29 observed against sensitive strain. 30 Significant increases in photoantimicrobial action of NRBr compared to NR, suggesting 31 that new azine derivative could be a promising PS for use in photodynamic inactivation 32 of S.aureus.