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Abstract
Photodynamic therapy (PDT) was discovered over 100 years ago by observing the killing
of microorganisms when harmless dyes and visible light were combined in vitro. Since
then it has primarily been developed as a treatment for cancer, ophthalmologic disorders
and in dermatology. However, in recent years interest in the antimicrobial effects
of PDT has revived and it has been proposed as a therapy for a large variety of localized
infections. This revival of interest has largely been driven by the inexorable increase
in drug resistance among many classes of pathogen. Advantages of PDT include equal
killing effectiveness regardless of antibiotic resistance, and a lack of induction
of PDT resistance. Disadvantages include the cessation of the antimicrobial effect
when the light is turned off, and less than perfect selectivity for microbial cells
over host tissue. This review will cover the use of PDT to kill or inactivate pathogens
in ex vivo tissues and in biological materials such as blood. PDT has been successfully
used to kill pathogens and even to save life in several animal models of localized
infections such as surface wounds, burns, oral sites, abscesses and the middle ear.
A large number of clinical studies of PDT for viral papillomatosis lesions and for
acne refer to its antimicrobial effect, but it is unclear how important this microbial
killing is to the overall therapeutic outcome. PDT for periodontitis is a rapidly
growing clinical application and other dental applications are under investigation.
PDT is being clinically studied for other dermatological infections such as leishmaniasis
and mycobacteria. Antimicrobial PDT will become more important in the future as antibiotic
resistance is only expected to continue to increase.