Novel Type of Water-Soluble Photosensitizer from Trichoderma reesei for Photodynamic Inactivation of Gram-Positive Bacteria

Abstract

sorbicillinoids obtained by microbial fermentation using T. reesei. Sorbicillinoids could effectively generate singlet oxygen under UV light irradiation, and ultimately display photoinactivation activity on Gram-positive bacteria, but not Gram-negative ones. More importantly, UV light can generally only be used to inactivate bacteria on the surface due to its weak penetration. However, it can penetrate deep into the solution and inactivate bacteria in the presence of sorbicillinoids. Therefore, sorbicillinoids, a type of secondary metabolite from fungus, has a promising future as a new PS for APDT using nontoxic dose of UV light irradiation.

Highly potent photoinactivation of bacteria using a water soluble, cell permeable, DNA-binding photosensitizer

“…Moreover, selective killing of bacteria can be readily achieved in the presence of mammalian cells. Br-DAPI’s sub-micromolar potency in both gram-negative and gram-positive bacteria make it superior to commonly employed phenothiazinium PSs like the FDA approved MB as demonstrated here, and to other recently reported PSs, which in addition to having lower potencies, often photoinactivate either gram-positive or gram-negative bacteria, but not both 10,16,35,36 . Given its high potency, bacterial selectivity over mammalian cells, and 2-photon excitability, Br-DAPI may be a promising stand-alone PS for treating more complex bacterial systems.…”

“…In contrast, bacteria treated with Br-DAPI and light reduced total genomic DNA of N99 E. Coli and B. subtilis by 74% and 73%, respectively (Figure 5). The lack of appearance of new bands at lower molecular weights is assumed to be due to ROS induced double-stranded DNA breaks, which lead to fragments at concentrations too low to detect by staining, as observed in previously reported PS photocleavage experiments 10, 22 . Overall, these experiments confirm that at least one molecular target of Br-DAPI is DNA, which may be one contributor to the observed high potency in gram-negative and gram-positive bacteria.…”

“…Given that Br-DAPI binds DNA, produces ROS and kills bacteria, we asked whether light-mediated ROS production causes DNA damage. To determine this, we performed a DNA photocleavage experiment as previously described 10 . Bacteria were treated with Br-DAPI (1 μM) for 5 minutes, irradiated (365 nm, 4.5 J cm −2 ) or kept in the dark, then the DNA was extracted and analyzed by agarose gel electrophoresis.…”

“…Genomic DNA was extracted from N99 E. coli and B. subtilis after treatment as reported in a previous study 10 using PureLink™ Genomic DNA Mini Kit (purchased from ThermoFisher Sceintific). 1 mL suspensions of bacteria from the overnight culture were incubated with Br-DAPI (0.5 μM; < 1% DMSO) for 5 minutes at 37°C and those designated for light treatment irradiated with a 365 nm LED for 5 minutes (4.5 J cm −2 ).…”

“…Despite its advantages over other antimicrobial therapies, the use of APDT for treating bacterial infections has been limited by the requirement for high concentrations of the PS and high doses of light to completely eliminate infectious bacteria cells, leading to surrounding host cell damage. Since most PSs have poor solubility in water, high concentrations often result in aggregation, which leads to poor APDT efficacy 9, 10 . To overcome this issue, PSs may be combined with other agents such as antimicrobial peptides 11 , liposomal systems 12 or biodegradable polymers 13 , or have small cationic groups or other moieties 14–16 conjugated to the PS.…”