Background: With the increasing emergence of multidrug-resistant (MDR) bacterial strains, there is a pressing need for the development of alternative treatment for infections. Antimicrobial blue light (aBL) has provided a simple and effective approach. <p> </p>Methods: We first investigated the effectiveness of aBL (415 nm) inactivation of USA300 LAClux (a communityacquired Methicillin-resistant Staphylococcus aureus strain) both in the planktonic and biofilm forms. The survival of the bacteria in suspensions was determined by serial dilution and that of the biofilm-embedded bacteria was determined by bioluminescence quantification. Using a mouse model of thermal burn infected with USA300 LAClux, we further assessed the effectiveness of aBL for treating localized infections. Bioluminescence imaging was performed to monitor in real time bacterial viability in vivo. <p> </p>Results: In vitro study showed that, for the planktonic counterpart of the bacteria or the 24-h-old biofilms, an irradiance of 55 mW/cm<sup>2</sup> for 60 min resulted in a 4.61 log<sub>10</sub> or 2.56 log<sub>10</sub> inactivation, respectively. In vivo study using infected mouse burns demonstrated that a 2.56-log<sub>10</sub> inactivation was achieved after 100-mW/cm<sup>2</sup> irradiation for 62 min. Conclusions: aBL is a potential alternative approach for treating Methicillin-resistant Staphylococcus aureus infections.
In this preclinical study, we investigated the utility of antimicrobial blue light therapy for <i>Candida albicans </i>infection in acutely burned mice. A bioluminescent strain of <i>C. albicans </i>was used. The susceptibilities to blue light inactivation were compared between<i> C. albicans </i>and human keratinocyte. <i>In vitro </i>serial passaging of<i> C. albicans </i>on blue light exposure was performed to evaluate the potential development of resistance to blue light inactivation. A mouse model of acute thermal burn injury infected with the bioluminescent strain of<i> C. albicans </i>was developed. Blue light (415 nm) was delivered to mouse burns for decolonization of <i>C. albicans</i>. Bioluminescence imaging was used to monitor in real time the extent of fungal infection in mouse burns. Experimental results showed that<i> C. albicans </i>was approximately 42-fold more susceptible to blue light inactivation in vitro than human keratinocyte (<i>P</i>=0.0022). Serial passaging of <i>C. albicans </i>on blue light exposure implied a tendency for the fungal susceptibility to blue light inactivation to decrease with the numbers of passages. Blue light reduced fungal burden by over 4-log<sub>10</sub> (99.99%) in acute mouse burns infected with <i>C. albicans </i>in comparison to infected mouse burns without blue light therapy (<i>P</i>=0.015).
Background: An increasing prevalence of Candida infections has emerged with the wide use of immune-suppressants and antibiotics. Current antifungal drugs exhibit low efficiency and high toxicity to the normal organs. Photodynamic inactivation (PDI) provides an alternative therapeutic strategy involving the use of photosensitizer (PS) and light irradiation. This study evaluated PDI effects against strains of C. albicans, C. parapsilosis, C. krusei and C. glabrata, using the PS of hematoporphyrin monomethyl ether (HMME), which is a second-generation PS clinically approved in China. Methods: Suspensions (~10<sup>6</sup> CFU/ml) were incubated with seven HMME concentrations (0.25~50 μM) for 30 min followed by 532-nm laser irradiation for 10 min at 40 mW/cm2. Viability of cells was assayed by CFU counting. Furthermore, fetal calf serum (10%) and singlet oxygen quencher sodium azide (100mM) were respectively added to the suspension of C. krusei to evaluate their roles in PDI process. Results: Among the four species, C. albicans was the most sensitive to PDI; 4 log<sup>10</sup> killing was achieved at the concentration of 7.5 μM. C. glabrata was the most resistant; 3 log<sub>10</sub> killing was not obtained even at PS concentration of 50 μM. PDI effects against C. krusei were inhibited by both serum and sodium azide. Conclusions: HMME-mediated PDI was able to effectively kill Candida in our experimental conditions, mainly through a Type Ⅱ photoprocess. However, the effects could be intensively reversed by the presence of serum. Thus, there might be a long way before HMME can be used in fighting against Candida in real infectious foci.
[Ru(bpy)<sub>2</sub>(dppn)]<sup>2+</sup>, one of Ru(II) polypyridyl complexes, present inner dicationic charge and high <sup>1</sup>O<sub>2</sub> quantum yield. In
this study, the synthetic compound was used as photosensitizer (PS) to photoinactivate a reference strain of
<i>Staphylococcus aureus </i>ATCC 25923. Bacterial suspensions consisting of 10<sup>8</sup> colony-forming units (CFU) per milliliter
were incubated with PS of different concentrations (0.025μM ~ 25μM). After a 30 minutes period, the suspensions
were exposed to 457nm laser light, determined by the absorption spectra of the PS in phosphate buffered saline (PBS),
with a power density of 40 mW/cm<sup>2</sup> for 10 minutes (energy density of 24 J/cm<sup>2</sup>). PS group, light group and the blank
control were also concerned. Viability of bacteria was determined by pour plates. The Log<sub>10</sub> reductions were calculated
and killing effects in photodynamic inactivation (PDI) group were analysed contrast to the blank control. We observed
that neither the laser light nor the PS per se had any inhibitory effect on the viability of the bacteria. PS at low dose
(0.025μM) followed by illumination yielded no significant decrease in the viable number. PS at 0.25μM and 2.5μM
with irradiation induced reductions of 1.69 Log<sub>10</sub> and 5.97 Log<sub>10</sub>, respectively. PS at 10μM and 25μM combined with
light brought viable bacterial cells down to undetectable levels (reductions < 7 Log<sub>10</sub>). We concluded that with the PS of
appropriate doses, [Ru(bpy)<sub>2</sub>(dppn)]<sup>2+</sup> mediated PDI inactivated S.aureus efficiently. At the concentration of 2.5μM,
bactericidal activity was reached where the viability of bacteria fell more than 3 Log<sub>10</sub> based on previous researches.