Abstract
The global spread of bacterial resistance to antibiotics promotes a search for alternative approaches to eradication of pathogenic bacteria. One alternative is using photosensitizers for inhibition of Gram-positive and Gram-negative bacteria under illumination. Due to low penetration of visible light into tissues, applications of photosensitizers are currently limited to treatment of superficial local infections. Excitation of photosensitizers in the dark can be applied to overcome this problem. In the present work, dark antibacterial activity of the photosensitizer Rose Bengal alone and in combination with antibiotics was studied. The minimum inhibitory concentrations (MIC) value of Rose Bengal against S. aureus dropped in the presence of sub-MIC concentrations of ciprofloxacin, levofloxacin, methicillin, and gentamicin. Free Rose Bengal at sub-MIC concentrations can be excited in the dark by ultrasound at 38 kHz. Rose Bengal immobilized onto silicon showed good antibacterial activity in the dark under ultrasonic activation, probably because of Rose Bengal leaching from the polymer during the treatment. Exposure of bacteria to Rose Bengal in the dark under irradiation by electromagnetic radio frequency waves in the 9 to 12 GHz range caused a decrease in the bacterial concentration, presumably due to resonant absorption of electromagnetic energy, its transformation into heat and subsequent excitation of Rose Bengal.
Highlights
The global growth and spread of bacterial resistance to antibiotics obligates a search for new approaches to eradication of pathogenic bacteria
In the present work we examined the dark activity of Rose Bengal several antibiotics against S. aureus by detection of minimum inhibitory concentrations (MIC)
Rose Bengal possesses dark antibacterial activity which is enhanced upon combination with antibiotics
Summary
The global growth and spread of bacterial resistance to antibiotics obligates a search for new approaches to eradication of pathogenic bacteria. Illumination of PSs by visible light leads to energy transfer from the excited PS molecules to dissolved molecular oxygen This leads to the formation of reactive oxygen species, which cause irreversible damage to the bacterial cells that ends in the cells’ death [1,2,3,4]. In our previous works we showed that PSs can be activated by chemiluminescent light generated by a chemiluminescent reaction of luminol in the absence of external illumination [13,14,15]. This method was shown to be efficient against Gram-positive S. aureus and Gram-negative E. coli when methylene blue was used as the PS
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