PDT kills drug-resistant bacteria, fungus in lab tests

Photodynamic therapy may be an effective treatment for fungal infections and certain bacterial infections of the oral cavity, including some that are resistant to antibiotics, research from the University at Buffalo’s School of Dental Medicine has shown. Researchers found that the bacteria S. mutans, as well as fungal organisms of the genus Candida, cultured from HIV patients, were highly susceptible to killing with minimal doses of PDT, both in laboratory dishes and on biofilms grown on denture material. Results of the research were presented March 10, 2006 at the International Association of Dental Research meeting in Orlando, Fla. “The results of the studies so far, while not completed, may have important implications in the treatment of oral infectious diseases currently confounding the medical and dental community,” said Thomas S. Mang, Ph.D., associate professor of oral and maxillofacial surgery and senior author on the study.

“PDT may provide an adjunct to current antibiotic treatment or an alternative where antibiotics no longer are working. This may be vital for patients undergoing cancer therapy, HIV patients who demonstrate resistance to antibiotics and the elderly with persistent oral infections.” Photodynamic therapy is based on the propensity of certain types of cells or organisms to absorb light-sensitive drugs. This selective retention allows researchers to direct a laser beam into the organism, which activates the drug and kills the organism but does not damage surrounding tissue.

PDT has been shown to be effective against certain types of cancer, particularly Kaposi’s sarcoma, cancer of the esophagus and breast cancer that has metastasized to the chest wall. The drug Photofrin® has been approved by the FDA as a sensitizer for PDT in the treatment of early and late stage endobronchial and esophageal cancers, as well as high-grade abnormal tissues associated with Barrett’s esophagus, a peptic ulcer of the lower esophagus caused by the presence of cells that normally stay in the stomach lining.

In the current research, after adding the light-sensitive drug Photofrin® to the cultured samples and biofilm, the samples were exposed to various intensities of light. Results showed that the photosensitizer accumulated in the samples within 15 minutes. Very low doses of light killed nearly all the S. mutans bacteria, reducing its concentration to less than 0.1 percent. PDT also demonstrated significant killing of three types of Candida: C. albicans, which causes thrush, and C. glabrata and C. krusei, in samples harvested from immunocompromised (HIV) patients.

Science Daily
April 11, 2006

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