Rehab Amin, PhD

Pseudomonas aeruginosa is among the most common pathogens that cause nosocomial infections and is responsible for about 10% of all hospital-acquired infections. In the present study, we investigated the potential development of tolerance of P. aeruginosa to antimicrobial blue light by carrying 10 successive cycles of sublethal blue light inactivation. The high-performance liquid chromatographic (HPLC) analysis was performed to identify endogenous porphyrins in P. aeruginosa cells. In addition, we tested the effectiveness of antimicrobial blue light in a mouse model of nonlethal skin abrasion infection by using a bioluminescent strain of P. aeruginosa. The results demonstrated that no tolerance was developed to antimicrobial blue light in P. aeruginosa after 10 cycles of sub-lethal inactivation. HPLC analysis showed that P. aeruginosa is capable of producing endogenous porphyrins in particularly, coproporphyrin III, which are assumed to be responsible for the photodynamic effects of blue light alone. P. aeruginosa infection was eradicated by antimicrobial blue light alone (48 J/cm(2) ) without any added photosensitizer molecules in the mouse model. In conclusion, endogenous photosensitization using blue light should gain considerable attention as an effective and safe alternative antimicrobial therapy for skin infections. Lasers Surg. Med. © 2016 Wiley Periodicals, Inc.

BACKGROUND:  Biofilms affect more than 80% bacterial infections in human and are usually difficult to eradicate due to their inherent drug resistance.

METHODS:  We investigated the effectiveness of antimicrobial blue light (aBL; 415 nm) inactivation of Acinetobacter baumannii or Pseudomonas aeruginosa biofilms in 96-well microplates and in infected mouse burns.

RESULTS:  In vitro in 96-well microplates, 24-h and 72-h old biofilms of A. baumannii exposed to 432 J/cm(2) aBL had 3.59- and 3.18-log10 inactivation, respectively. For P. aeruginosa biofilms, a similar 3.02- and 3.12-log10 inactivation was achieved. In mouse burns infected with 5×10(6) CFU of A. baumannii, approximately 360 and 540 J/cm(2) aBL was required to achieve 3-log10 inactivation of biofilms when aBL was delivered at 24 and 48 h post-inoculation, respectively. High-performance liquid chromatography (HPLC) analysis revealed the presence of endogenous porphyrins in both A. baumannii and P. aeruginosa cells. Using the TUNEL assay, no apoptotic cells were detected in aBL-irradiated mouse skin at up to 24 h after aBL exposure (540 J/cm(2)).

CONCLUSIONS:  aBL has antimicrobial activity in biofilms of A. baumannii and P. aeruginosa, and is a potential approach for biofilm-related infections.

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