Photodynamic therapy (PDT) is an alternative to conventional therapies of infections. It can kill drug-resistant bacteria without damaging host tissues. In the present work we use the multiresistant strain PA21 of Pseudomonas aeruginosa to model a wound infection in mice and study the effect of PTD mediated by aqueous solutions of the anionic photosensitizer merocyanine 540 (solubilized in water and in 0.25 M sodium chloride) on bacterial decontamination and wound healing. To assess a therapeutic effect of PDT, we monitored bacterial contamination of the wound, measured the wound size in two planes using a caliper and carried out a histopathological examination of infected tissue sections. Our study reveals that PDT mediated by MC540 in the sodium chloride solution can induce bacterial death, inhibit bacterial re-growth and accelerate wound healing.