Targeted photodynamic therapy of established soft-tissue infections in mice

Abstract

The worldwide rise in antibiotic resistance necessitates the development of novel antimicrobial strategies. Although many workers have used photodynamic therapy (PDT) to kill bacteria in vitro, the use of this approach has seldom been reported in vivo in animal models of infection. We have previously described the first use of PDT to treat excisional wound infections by Gram-(-) bacteria in living mice. However, these infected wound models involved a short timespan between infection (30 min) and treatment by PDT. We now report on the use of PDT to treat an established soft-tissue infection in mice. We used Staphylococcus aureus stably transformed with a Photorhabdus luminescenslux operon (luxABCDE) that was genetically modified to be functional in Gram-(+) bacteria. These engineered bacteria emitted bioluminescence, allowing the progress of the infection to be monitored in both space and time with a low light imaging charge-coupled device (CCD) camera. One million cells were injected into one or both thigh muscles of mice that had previously been rendered neutropenic by cyclophosphamide administration. Twenty-four hours later, the bacteria had multiplied more than one hundredfold; poly-L-lysine chlorin e6 conjugate or free chlorin e6 was injected into one area of infected muscle and imaged with the CCD camera. Thirty minutes later, red light from a diode laser was delivered as a surface spot or by interstitial fiber into the infection. There was a light dose dependent loss of bioluminescence (to <5% of that seen in control infections) not seen in untreated infections or those treated with light alone, but in some cases, the infection recurred. Treatment with conjugate alone led to a lesser reduction in bioluminescence. Infections treated with free chlorin e6 responded less well and the infection subsequently increased over the succeeding days, probably due to PDT-mediated tissue damage. PDT-treated infected legs healed better than legs with untreated infections. This data shows that PDT may have applications in drug-resistant soft-tissue infections.

Photodynamic antimicrobial therapy

“…The influence of PACT on infected wounds, burns, infection of soft tissues, disorders caused by Helicobacter pylori, and brain abscess have been evaluated. Application of PS and local irradiation in mice showed a significant reduction of bacteria infected wounds and burns, better healing of wounds and no sepsis developed [43,44]. In a study on rats, it was possible to eradicate Porphyromonas gingivalis in the periodontal pockets surrounding the affected tooth by using PACT (toluidine blue as a photosensitive substance).…”

Dirty hands: photodynamic killing of human pathogens like EHEC, MRSA and Candida within seconds

“…Recently photodynamic treatment of microorganisms has been shown to be very effective in vitro as well as in vivo. [14][15][16][17][18][19] Photodynamic inactivation of microorganisms is based on the concept of positively charged photosensitizers that can attach and/or accumulate in or at the pathogen to induce irreversible damage upon light activation of the photosensitizer. 20,21 The absorption of light by a photosensitizer leads to the generation of reactive oxygen species such as singlet oxygen which induces irreversible oxidative damage of the pathogens during illumination.…”

Antimicrobial photodynamic therapy combined with conventional endodontic treatment to eliminate root canal biofilm infection

“…Our laboratory has employed bioluminescent imaging as a convenient means to monitor the effectiveness of antimicrobial PDT in animal models of infections caused by several bioluminescent pathogens [38]. This methodology has been demonstrated in mouse models of infected wounds [39,40] burns [41] and abscesses [42] using both Gram-positive and Gram-negative bacteria.…”