Sensitivity of Staphylococcus aureus and Pseudomonas aeruginosa to Blue Light Irradiation for Possible Role in Antimicrobial Therapy
Dr. Abhijeet Mane,
Department of Microbiology, Bharati Vidyapeeth Deemed to be University Medical College, Pune-411043, Maharashtra, India.
Introduction: Due to the escalation of antibiotic resistant pathogens, non-antibiotic approaches to clinical treatment are being investigated, particularly phototherapy. In this study, 470 nm blue light was examined as an antimicrobial agent against various isolates of S. aureus and P. aeruginosa in vitro.
Aim: To determine the adequacy of blue light as an antimicrobial agent against the two pathogens infamous for rapid development of drug resistance.
Materials and Methods: ATCC strains of each organism, along with 25 strains of each from patient isolates, were collected. Isolates were suspended in peptone water at 0.5McF, and then inoculated on plates of Mueller-Hinton agar (control and experimental plate). Antibiotic sensitivity of each isolate was determined with 7 common antibiotics, following which, experimental plates were irradiated with a 470 nm Light Emitting Diode (LED) for 60 minutes. Plates were then placed in incubators overnight at 37°C. Zones of inhibition for each experimental plate were compared with the control to determine any action of the blue LED with the antibiotics. Results of the study were analysed using paired t-test where p<0.05 and was calculated for all drugs which showed significant increase in zones of inhibition following 470 nm blue light irradiation.
Results: Results demonstrated an increase in zones by 0 to 6 mm, though this was predominantly seen in isolates of P.aeruginosa. The action of the LED was particularly significant with Linezolid for S.aureus and Imipenem for P.aeruginosa, where there was a mean increase of 2 mm and 3 mm, respectively. Comparison of Ciprofloxacin in both pathogens demonstrated a greater increase of zones in plates of P.aeruginosa (2.23 cm) as compared to S.aureus (1.27 cm), suggesting greater sensitivity of this organism to the 470 nm light.
Conclusion: This study determined that 470 nm blue light does demonstrate a species-specific inhibitory effect on S.aureus and P.aeruginosa and can act synergistically with antibiotics. With further research regarding its mechanism of action and safety, blue light therapy may be implemented into clinical treatment of skin, wound and burn infections as an adjunct to antibiotics.