Mechanistic Aspects of the Photodynamic Inactivation of Vancomycin-Resistant Enterococci Mediated by 5-Aminolevulinic Acid and 5-Aminolevulinic Acid Methyl Ester

Abstract

Vancomycin-resistant Enterococci (VRE) is a serious concern for public health. Serious infections with VRE have very limited effective antimicrobial therapy, and alternative treatment approaches are highly desirable. One promising approach might be the photodynamic antimicrobial chemotherapy. In the present study, we investigated the photodynamic inactivation (PDI) of two VRE strains mediated by 5-aminolevulinic acid (5-ALA) and its derivative 5-ALA methyl ester (MAL). The photodynamic damages to bacteria on the level of genomic DNA, the leakage of cell components, and the changes of membrane structure were investigated. After treated with 10 mM 5-ALA and irradiated by the 633 ± 10 nm LED for 60 min, 5.37 and 5.22 log10 reductions in bacterial survival were achieved for the clinical isolate of VRE and E. faecalis (ATCC 51299), respectively. After treated with 10 mM MAL and irradiated by the LED for 60 min, 5.02 and 4.91 log10 reductions in bacterial survival were observed for the two VRE strains, respectively. In addition, the photocleavage on genomic DNA and the rapid release of intracellular biopolymers were detected in PDI-treated bacteria. The intensely denatured cytoplasm and the aggregated ribosomes were also found in PDI-treated bacteria by transmission electron microscopy. Although 5-ALA and MAL-mediated PDI could induce the photocleavage on genomic DNA, the PDI of the two VRE strains might be predominantly attributed to the envelope injury, the intracellular biopolymers leakage, and the cytoplasm denature.

Photodynamic Antibiofilm and Antibacterial Activity of a New Gel with 5-Aminolevulinic Acid on Infected Titanium Surfaces

“…By comparison, previous literature that used different formulations of aminolevulinic acid followed by photodynamic therapy (ala-PDI) showed contradictory results, especially on Gram-negative bacteria [36,37]. It was shown that the increase in reactive oxygen species (ROS) induced by ala-PDI promotes intracellular biopolymer leakage, photocleavage on genomic DNA, cytoplasm denaturing, and envelope injury [38].…”

Validation of stable reference genes in Staphylococcus aureus to study gene expression under photodynamic treatment: a case study of SEB virulence factor analysis

“…Apart from a recent observation that S. aureus tolerated treatment with 15 consecutive cycles of passages under sublethal aPDI conditions 11 , no resistance selection for aPDI has been shown thus far. aPDI effectively eradicates a wide group of multidrug-resistant bacteria in vitro (planktonic and biofilm cultures), e.g., vancomycin-resistant Enterococcus faecalis (VRE) (5.37 log 10 unit reduction in survival) 12 , a methicillin-resistant S. aureus (MRSA) strain (5–6 log 10 unit reduction) 13 , and extended-spectrum β-lactamase (ESBL)-producing K. pneumoniae . Effective biofilm reduction under aPDI was also documented 14 .…”

Photoinactivation of ESKAPE Pathogens: Overview of Novel Therapeutic Strategy

“…Treatment with 5-ALA resulted in 5.37 log 10 reduction in survival fraction for VRE clinical isolate and 5.22 log 10 for the reference E. faecalis strain. Slightly lower efficiency was observed in case of MAL treatment reaching 5.02 and 4.91 log 10 reduction in survival fraction for the clinical and reference strains, respectively [11]. Another study concerning in vitro planktonic conditions was reported by Borba et al, who described the effectiveness of erythrosine and LED lamp emitting blue wavelength light (440-480 nm).…”