Abstract
The ability of pathogenic bacteria acquire resistance to the existing antibiotics has long been considered a dangerous health risk threat. Currently, the use of visible light has been considered a new approach to treat bacterial infections as an alternative to antibiotics. Herein, we investigated the antimicrobial effect of two range of visible light, blue and red, on Staphylococcus aureus and Pseudomonas aeruginosa, two pathogenic bacterial commonly found in healthcare settings-acquired infections and responsible for high rate of morbidity and mortality. Bacterial cultures were exposed to blue or red light (470 nm and 660 nm) provided by light-emitting diodes - LED. The fluencies and irradiance used for blue and red light were 284.90 J/cm2, 13.19 mW/cm2 and 603.44 J/cm2, 27.93 mW/cm2 respectively. Different experimental approaches were used to determine the optimal conditions of light application. Only exposure to blue light for 6 hours was able to inhibit about 75% in vitro growth of both bacterial species after 24 hours. The surviving exposed bacteria formed colonies significantly smaller than controls, however, these bacteria were able to resume growth after 48 hours. Blue light was able to inhibit bacterial growth upon inoculation in both saline solution and BHI culture medium. We can conclude that blue light, but not red light, is capable of temporarily retarding the growth of gram negative and gram positive bacteria.
Highlights
Antibiotic resistance is among the most important public health threats of the 21st century (WHO, 2014)
LEDS positioned at 3 mm from the surface of solid medium increased the temperature from 27 °C to more were not observed for both bacterial lineages exposed to red light, 0.51 ± 0.1 mm for S. aureus and 0.75 ± 0.03 mm for P. aeruginosa (Figure 2A)
Since light have physical properties that can be influenced by different material while it passes through, we sought to investigate if plates made by plastic or glass could influence the inhibitory effect observed with the exposure of bacterial culture to blue light
Summary
Antibiotic resistance is among the most important public health threats of the 21st century (WHO, 2014). The inappropriate, excessive and careless use of antibiotics is the single most important factor associated to this resistance (Chambers and Deleo, 2009; Schwarz et al, 2017; Khan et al, 2017). S. aureus (Gram-positive facultative anaerobe bacterium) and P. aeruginosa (Gram-negative facultative anaerobe bacterium) are important pathogens due to its abundance in various types of environment its and ability to cause both local superficial infections as more severe invasive infections (Chambers and Deleo, 2009; Falkinham III et al, 2015; Oliver et al, 2015; Chaney et al, 2017; Feng et al, 2017; Monaco et al, 2017; Freitas et al, 2018)
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