Approaches to unravel pathways of reactive oxygen species in the photoinactivation of bacteria induced by a dicationic fulleropyrrolidinium derivative.

The photodynamic mechanism sensitized by N,N-dimethyl-2-[4-(3-N,N,N-trimethylammoniopropoxy)phenyl]fulleropyrrolidinium (DPC ₆₀ ²⁺ ) was investigated in Staphylococcus aureus cells. Different experimental conditions were used to detect reactive oxygen species (ROS) in S. aureus cell suspensions. First, a photoinactivation of 4 log decrease of S. aureus viability was chosen using 0.5μM DPC ₆₀ ²⁺ and 15min irradiation. An anoxic atmosphere indicated that oxygen was required for an effective photoinactivation. Also, photoprotection was found in the presence of sodium azide, whereas the photocytotoxicity induced by DPC ₆₀ ²⁺ increased in D ₂ O. The addition of diazabicyclo[2.2.2]octane or d-mannitol produced a reduction in the S. aureus photokilling. Moreover, singlet molecular oxygen, O ₂ ( ¹ Δ _g ), was detected by the reaction with 9,10-dimethylanthracene into the S. aureus cells. A decrease in the photoinactivation of S. aureus was observed in the presence of β-nicotinamide adenine dinucleotide reduced form, which was dependent on the NADH concentration. Therefore, under aerobic condition the photocytotoxicity activity induced by DPC ₆₀ ²⁺ was mediated by mainly a contribution of type II process. Moreover, photoinactivation of S. aureus was possible with DPC ₆₀ ²⁺ in the presence of azide anions under anoxic condition. However, these conditions were not effective to photoinactivate Escherichia coli. On the other hand, the addition of potassium iodide produced an increase in the photokilling of bacteria, depending on the KI concentration and irradiation times. The formation of reactive iodine species may be contributing to inactivate S. aureus cells photoinduced by DPC ₆₀ ²⁺ .
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