In situ monitoring of photodynamic inactivation of the membrane functions of bacteria using electrochemical sensors.

The photodynamic inactivation of the membrane functions of bacteria was analyzed in situ, using K(+) and tetraphenylphosphonium (TPP(+)) electrodes, as well as an oxygen electrode. Tetrakis(4-N-trimethylaminophenyl)porphine (TTMAPP) and rose bengal were used, since both dyes act strongly on bacteria, such as Staphylococcus aureus. After a short time lag, they inhibited the respiration of bacteria and increased the permeability of the cytoplasmic membrane to K(+), while dissipating the membrane potential. This combination of sensors is quite useful for visualizing the actions of photosensitizers on the bacterial membrane. TTMAPP and rose bengal impaired the bacterial function by reducing the membrane potential within minutes of photo-irradiation.