Bacterial resistance against antibiotic treatment is becoming an increasing problem in medicine. Therefore methods tc, destroy microorganisms by other means are being investigated, one of which is photodynamic therapy (PDT).It has already been shown that a variety of Gram-positive and Gram-negative bacteria can be killed in vitro by PDT using exogenous sensitizers. An alternative method of photosensitizing cells is to stimulate the production of endogenous sensitizers. The purpose of this study was to investigate the bactericidal efficacy of PDT for Huemophilusparuin~~~enzue with endogenously produced porphyrins, synthesized in the presence of Saminolaevulinic acid (GALA).H. paruinjkuxzue incubated with increasing amounts of GALA showed decreased survival after illumination with 630 nm light. No photodynamic effect on the bacterial viability was found when H. pczruinjluenzae was grown without added &ALA. H. influenzue, grown in the presence of S-ALA, but not capable of synthesizing porphyrins from GALA, was not affected by PDT. Of the range of incident wavelengths, 617 nm appeared to be the most efficient in killing the bacteria. Spectrophotometry of the bacterial porphyrins demonstrated that the maximum fluorescence occurred at approximately 617 nm, with a much lower peak around 680 nm. We conclude that a substantial killing of H. puruinjluenzue by PDT in vitro after endogenous sensitization with 6-A:LA can be achieved. 0 1997 Elsevier Science S.A.

Virulence factors are required to cause infections. Previous work has shown that the spatial organization of a population, such as a biofilm, can increase the production of some virulence factors, including pyoverdine, which is produced by Pseudomonas aeruginosa .

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