The Effect of Photoactivated TMP on \u3cem\u3eBurkholderia cepacia\u3c/em\u3e Biofilms

Burkholderia cepacia is an opportunistic pathogen that causes infections in immunocompromised individuals such as cystic fibrosis patients. B. cepacia infections are typically characterized by the formation of complex communities of cells known as biofilms. Because B. cepacia biofilms are difficult to eradicate using antibiotics, it is important to pursue alternative treatment methods. Photodynamic therapy (PDT) is a type of therapy that uses light, a photosensitizer, and oxygen to elicit cell death through the production of reactive oxygen species. PDT has been shown in previous studies to be successful in killing both Pseudomonas aeruginosa and Staphylococcus aureus. In this study, we examined the effect of a cationic porphyrin on B. cepacia biofilms by exposing static biofilms to 5,10,15,20-tetrakis(1-methyl-pyridino)-21H,23H-porphine, tetra-p-tosylate salt (TMP) followed by irradiation. Standard plate counts of cells recovered from attached biofilms revealed a 0.7-log10 reduction (80.2%) in cell viability in the presence of 225µM of TMP and light. In addition, there was a 2.74-log(10) reduction in cell viability when biofilms were treated with TMP and ciprofloxacin in comparison to a 1.96-log(10) reduction when biofilms were treated with ciprofloxacin alone. Because surface motility is involved in biofilm formation, we also examined the effects of TMP on swarming motility in B. cepacia and P. aeruginosa. In the presence of TMP in the dark, there was a substantial increase in swarming motility of both B. cepacia and P. aeruginosa. These results suggest that photoactivated TMP not only kills biofilm-associated cells, but may promote biofilm disruption through pre-dispersion behavior in the absence of light