Antimicrobial Photodynamic therapy enhanced by the peptide aurein 1.2.

In the past few years, the World Health Organization has been warning that the post-antibiotic era is an increasingly real threat. The rising and disseminated resistance to antibiotics made mandatory the search for new drugs and/or alternative therapies that are able to eliminate resistant microorganisms and impair the development of new forms of resistance. In this context, antimicrobial photodynamic therapy (aPDT) and helical cationic antimicrobial peptides (AMP) are highlighted for the treatment of localized infections. This study aimed to combine the AMP aurein 1.2 to aPDT using Enterococcus faecalis as a model strain. Our results demonstrate that the combination of aPDT with aurein 1.2 proved to be a feasible alternative capable of completely eliminating E. faecalis employing low concentrations of both PS and AMP, in comparison with the individual therapies. Aurein 1.2 is capable of enhancing the aPDT activity whenever mediated by methylene blue or chlorin-e6, but not by curcumin, revealing a PS-dependent mechanism. The combined treatment was also effective against different strains; noteworthy, it completely eliminated a vancomycin-resistant strain of Enterococcus faecium. Our results suggest that this combined protocol must be exploited for clinical applications in localized infections as an alternative to antibiotics.

Phototherapeutic spectrum expansion through synergistic effect of mesoporous silica trio-nanohybrids against antibiotic-resistant gram-negative bacterium.

The extensive impact of antibiotic resistance has led to the exploration of new anti-bacterial modalities. We designed copper impregnated mesoporous silica nanoparticles (Cu-MSN) with immobilizing silver nanoparticles (SNPs) to apply photodynamic inactivation (PDI) of antibiotic-resistant E. coli. SNPs were decorated over the Cu-MSN surfaces by coordination of silver ions on diamine-functionalized Cu-MSN and further reduced to silver nanoparticles with formalin. We demonstrate that silver is capable of sensitizing the gram-negative bacteria E. coli to a gram-positive specific phototherapeutic agent in vitro; thereby expanding curcumin's phototherapeutic spectrum. The mesoporous structure of Cu-MSN remains intact after the exterior decoration with silver nanoparticles and subsequent curcumin loading through an enhanced effect from copper metal-curcumin affinity interaction. The synthesis, as well as successful assembly of the functional nanomaterials, was confirmed by various physical characterization techniques. Curcumin is capable of producing high amounts of reactive oxygen species (ROS) under light irradiation, which can further improve the silver ion release kinetics for antibacterial activity. In addition, the positive charged modified surfaces of Cu-MSN facilitate antimicrobial response through electrostatic attractions towards negatively charged bacterial cell membranes. The antibacterial action of the synthesized nanocomposites can be activated through a synergistic mechanism of energy transfer of the absorbed light from SNP to curcumin.

Violet 405 nm light: A novel therapeutic agent against ß-lactam-resistant Escherichia coli.

BACKGROUND AND OBJECTIVE: Approximately 1.7 million patients are affected by hospital-acquired infections every year in the United States. The increasing prevalence of multidrug-resistant bacteria associated with these infections prompts the investigation of alternative sterilization and antibacterial therapies. One method currently under investigation is the antibacterial properties of visible light. This study examines the effect of a visible light therapy (VLT) on ß-lactam-resistant Escherichia coli, a common non-skin flora pathogen responsible for a large percentage of indwelling medical device-associated clinical infection. MATERIALS AND METHODS: 405 nm light-emitting diodes were used to treat varying concentrations of a common laboratory E. coli K-12 strain transformed with the pCIG mammalian expression vector. This conferred ampicillin resistance via expression of the ß-lactamase gene. Bacteria were grown on sterile polystyrene Petri dishes plated with Luria-Bertani broth. Images of bacterial growth colonies on plates were processed and analyzed using ImageJ. Irradiance levels between 2.89 ± 0.19 and 9.45 ± 0.63 mW cm(-2) and radiant exposure levels between 5.60 ± 0.39 and 136.91 ± 4.06 J cm(-2) were tested. RESULTS: VLT with variable irradiance and constant treatment time (120 minutes) demonstrated significant reduction (P < 0.001) in E. coli between an irradiance of 2.89 mW cm(-2) (81.70%) and 9.37 mW cm(-2) (100.00%). Similar results were found with variable treatment time with constant irradiance. Log10 reduction analysis produced between 1.98 ± 0.53 (60 minute treatment) and 6.27 ± 0.54 (250 minute treatment) log10 reduction in bacterial concentration (P < 0.001). CONCLUSIONS: We have successfully demonstrated a significant bacterial reduction using high intensity 405 nm light. Illustrating the efficacy of this technology against a ß-lactam-resistant E. coli is especially relevant to the need for novel methods of sterilization in healthcare settings. These results suggest that VLT using 405 nm light could be a suitable clinical option for eradication of ß-lactam-resistant E. coli. Visible light kills statistically significant concentrations of E. coli. Antibiotic-resistant Gram-negative bacteria exhibits sensitivity to 405 nm light. Greater than 6 log10 reduction in ß-lactam-resistant E. coli when treated with visible light therapy.

Photo-activated porphyrin in combination with antibiotics: therapies against Staphylococci.

Staphylococcal infections have become difficult to treat due to antibiotic insensitivity and resistance. Antimicrobial combination therapies may minimize acquisition of resistance and photodynamic therapy is an attractive candidate for these combinations. In this manuscript, we explore combined use of antibiotics and meso-tetra (4-aminophenyl) porphine (TAPP), a cationic porphyrin, for treatment of Staphylococcus aureus contamination. We characterize the antimicrobial activity of photoactivated TAPP and show that activity is largely lost in the presence of a radical scavenger. Importantly, TAPP can be reactivated with continued, albeit attenuated, antibacterial activity. We then show that the antimicrobial activity of illuminated TAPP is additive with chloramphenicol and tobramycin for S. aureus and Escherichia coli, and synergistic for MRSA and Staphylococcus epidermidis. Chloramphenicol+methylene blue, another photosensitizer, also show additivity against S. aureus. In contrast, ceftriaxone and vancomycin do not strongly augment the low level effects of TAPP against S. aureus. Eukaryotic cells exhibit a dose-dependent toxicity with illuminated TAPP. Our results suggest that even sub-minimum inhibitory concentrations of photo-activated TAPP could be used to boost the activity of waning antibiotics. This may play an important role in treatments reliant on antibiotic controlled release systems where augmentation with photo-active agents could extend their efficacy.

In vitro resistance selection studies of RLP068/Cl, a new Zn(II) phthalocyanine suitable for antimicrobial photodynamic therapy.

Resistance to antimicrobial agents is emerging in a wide variety of nosocomial and community-acquired pathogens. The development of alternative therapies against nosocomial infections caused by clinically relevant pathogens represents a major public health concern. RLP068/Cl is a novel Zn(II) phthalocyanine proposed as a photosensitizer suitable for antimicrobial photodynamic therapy (APDT) for localized infections. Its ability, following activation by light, to induce resistance in three major human pathogens after 20 daily passages was studied. Simultaneously for the same strains, the ability of daily sequential subcultures in subinhibitory concentrations of RLP068/Cl to develop resistant mutants without illumination was evaluated. We demonstrate that 20 consecutive APDT treatments with RLP068/Cl did not result in any resistant mutants and that, in dark conditions, only Staphylococcus aureus strains had increased MICs of RLP068/Cl. However, even in this case, the susceptibility of the mutated bacteria to APDT was not affected by their MIC increase.