The Effects of Blue Light and Antibiotic Synergistic Treatments on Biofilms

The Synergistic Effect of Blue Light and Antibiotics on Pseudomonas aeruginosa Biofilms

Day by day the treatment of infectious pathogens is becoming more difficult due to antibiotic resistance. Of these increasingly resistant microorganisms, Pseudomonas aeruginosa is one of the most relevant, infecting surface burns, medical equipment, and implants due to its multidrug-resistant nature and ability to grow in biofilms. Therefore, P. aeruginosa’s medical relevance and resistant nature warrant the use of novel treatment techniques. For these reasons, blue light irradiation, both on patient wounds and other surfaces, is being investigated. Blue wavelengths are intrinsically antimicrobial and work by exciting intracellular porphyrins leading the production of fatal reactive oxygen species. One important benefit of blue light therapy is that its wavelengths do not injure surrounding native cells, allowing for the clinical targeting of pathogens. Blue light has also been shown to kill otherwise antibiotic-resistant organisms but is limited in its ability to fully eradicate a resistant biofilm due to incomplete penetration. Therefore, in this experiment the synergistic properties between blue light and two antibiotics—neomycin and tetracycline—were investigated. Synergy is defined as two antimicrobials having greater action when paired than independently. The minimum inhibitory concentration (MIC) of each antibiotic was determined, and a specific concentration range established around each. P. aeruginosa biofilms were then treated with varying concentrations of neomycin or tetracycline with half the biofilms being irradiated with blue light. Results analysis indicated that there was no synergistic effect between the antibiotics and blue light irradiation. Antibiotic concentration, however, played a significant role in the degree of biofilm inhibition and destruction.