Antimicrobial blue light inactivation of biofilms formed by clinical isolates of multidrug-resistant microorganisms

Antibiotic resistance is one of the most serious threats to public health. It is estimated that at least 23,000 people die each year in the USA as a direct result of antibiotic-resistant infections. In addition, many antibiotic-resistant microorganisms develop biofilms, surface-associated microbial communities that are extremely resistant to antibiotics and the immune system. A light-based approach, antimicrobial blue light (aBL), has attracted increasing attention due to its intrinsic antimicrobial effect without the involvement of exogenous photosensitizers. In this study, we investigated the effectiveness of this non-antibiotic approach against biofilms formed by multidrug-resistant (MDR) microorganisms. MDR Acinetobacter baumannii, Escherichia coli, Candida albicans, and Pseudomonas aeruginosa biofilms were grown either in 96-well microtiter plates for 24 h or in a CDC biofilm reactor for 48 h, and then exposed to aBL at 405 nm emitted from a light-emitting diode (LED). We demonstrated that, for the biofilms grown in the CDC biofilm reactor, approximately 1.88 log(10) CFU reduction was achieved in A. baumannii, 2.78 log(10) CFU in E. coli and 3.18 log(10) CFU in P. aeruginosa after 162 J/cm(2), 576 J/cm(2) and 500 J/cm(2) aBL were delivered, respectively. For the biofilms formed in the 96-well microtiter plates, 5.67 and 2.46 log(10) CFU reduction was observed in P. aeruginosa and C. albicans polymicrobial biofilm after an exposure of 216 J/cm(2). In conclusion, aBL is potentially an alternative non-antibiotic approach against MDR biofilm-related infections. Future studies are warranted to investigate other important MDR microorganisms, the mechanism of action of aBL, and aBL efficacy in vivo.