In Vitro Photodynamic Eradication of Pseudomonas aeruginosa in Planktonic and Biofilm Culture

Abstract

Photodynamic disinfection (PDD) is a nonantibiotic approach to treating drug-resistant bacterial infections. Pseudomonas aeruginosa, an opportunistic pathogen, is problematic because of its propensity to develop antibiotic resistance and its ability to secrete a protective biofilm matrix. This study examined the ability of PDD to eradicate planktonic and biofilm cultures of P. aeruginosa in vitro. Planktonic P. aeruginosa cultures were briefly exposed to a methylene blue-based photosensitizer formulation and subjected to energy doses ranging from 1.7 to 20.6 J cm )2 using a 670 nm nonthermal diode laser. Biofilms were grown for 24 and 48 h and exposed to photosensitizer for 30 s before illumination with 13.2 or 26.4 J of energy. A single exposure of planktonic P. aeruginosa to photosensitizer at >15.5 J cm )2 resulted in 100% eradication (>7 log 10 reduction from control), an effect that could be decreased significantly in the presence of the singlet oxygen quenchers L L-tryptophan and sodium azide. Decreasing the energy dose below this threshold by varying both power density and illumination duration resulted in a dose-dependent decrease in bacterial kill. In addition, 24 h biofilm viability was reduced by 99% with single exposure and 99.9% with double exposure, while 48 h biofilm viability was reduced by >99.999% with both single and double exposures. This study shows that PDD is effective in eradicating planktonic and biofilm cultures of P. aeruginosa, supporting the concept that translation into clinical practice for indications such as otitis externa and wound disinfection is a viable option.

A clinical study of photodynamic therapy for chronic skin ulcers in lower limbs infected with Pseudomonas aeruginosa

“…Based on the coloring conditions after culture, bacterial identification results could be accurately obtained in a short time period. Patients who had bacterial culture results that were positive for PA after 3 days and who met the inclusion criteria were included in the study [27].…”

“…However, the specific mechanism for this action requires further elucidation. Additionally, Street et al [27]. demonstrated that methylene blue-based PDT at a dose [15.5 J/cm 2 could completely eradicate planktonic PA and inhibit biofilms at a rate of 99 %.…”

The impact of antimicrobial photodynamic therapy in an artificial biofilm model

“…Development of bacterial resistance has not yet been shown and could not be generated in an experimental study protocol [14]. aPDT was shown to be able to eliminate the specific periodontopathogenic bacterium Aggregatibacter actinomycetemcomitans in a planktonic biofilm model [15], and to effectively eradicate planktonic and biofilm cultures of the opportunistic pathogen Pseudomonas aeruginosa [16]. Moreover, multispecies microbial biofilms and suspensions of microorganisms were developed from dental plaque samples and treated photodynamically.…”

Chapter 13. Antimicrobial Photodynamic Therapy (aPDT) for Oral Infections

“…Reasons for this variability, while likely in part due to small sample sizes of studies published to date, can be theorized from preclinical studies that preceded this clinical work. As demonstrated in several preclinical aPDT studies, 51,97,98 the importance of delivering an optimal activating light energy dose cannot be understated. While it is difficult to pinpoint a precise power density or energy dose threshold for clinical use using preclinical results, it is clear that antibacterial efficacy drops off dramatically when insufficient light is delivered to the site of treatment.…”