Results published by Gad et al. indicated that extracellular slime significantly influences PS uptake by S. aureus cells, PRN1371 manufacturer however an unambiguous conclusion was not possible due to the significant differences in both the uptake and PDI efficacy of the three PS tested, namely chlorine e6 , poly-L-lysine-chlorine e6 and methylene blue [48]. S. aureus strains tested in our experimental conditions expressed no statistical correlation Stattic order between PS uptake and PDI effectiveness, nevertheless the highest accumulation of PS was observed for the most efficiently killed strain 472 (3.4 log10 reduction in viable

count units), as well as the lowest PS accumulation was observed in the case of the most resistant to PDI – strain 1397 (0.2 log10 reduction in viable count units) (Figure 3). The mean uptake level was 47.4 μg/mg of total protein content and 7.3 μg/mg of total protein content, for strains 472 and 1397, respectively. The results concerning uptake level in strains 472 and 1397 remain in a good agreement with our previous reports, where the same set of clinical isolates was analyzed but with the use of a different PS, namely PpIXArg2 [25]. Based on our previous and present results we conclude that the PS uptake process is not the main determinant of PDI effectiveness, at least for the porphyrin-based photokilling. We and other authors propose subsequent

factors which may contribute and explain the differences in PDI efficacy of bacteria [25, 49], eg. cellular repair systems or level of antioxidant enzymes. Sod AZD1390 research buy activity and transcript level increase after PDI in PDI-susceptible strains The participation of superoxide

dismutase in oxidative stress resistance, and also in photodynamically generated reactive oxygen species is obvious. However, the role of Sod activity in PDI of bacteria has not been studied so far. There is few literature data on the association of Sod activity and photodynamic inactivation studies, and to the best of our knowledge they all concern eukaryotic cells. It was proposed for example that inhibition of Mn-Sod activity potentiates the antitumor effectiveness of photodynamic therapy in several cell lines and also in a mouse model old of tumorigenesis [50]. Our attempt was to assess Sod activity in clinical isolates of S. aureus and to compare its basic level between PDI-resistant and PDI-susceptible bacteria. Basic Sod activity levels differed only slightly between PDI-resistant and PDI-susceptible strains (33.2 ± 15 U/mg and 23.6 ± 4 U/mg, respectively), which can be expected as S. aureus is not constantly exposed to elevated levels of oxidative stress After PDI treatment we observed about a 4-fold increase of Sod activity but only in strains susceptible to PDI. Sod expression is probably induced by a particular signal.