Aspects of Photodynamic Inactivation of Bacteria

Increasing resistance of bacteria to antibiotics is a serious worldwide problem, and to combat resistant bacteria, new antibacterial approaches are to be developed. One alternative to traditional antibiotic therapy is photodynamic antimicrobial chemotherapy (PACT). PACT is based on excitation of photosensitizers (PS) capable of transferring the absorbed light energy to dissolved molecular oxygen causing generation of reactive oxygen species, which irreversibly damage bacterial cell components. The overall efficiency of PACT has been proven for Gram-positive and Gram-negative bacteria. The effectiveness of PACT can be increased by encapsulation of PS in liposomes providing more concentrated delivery of PS, enhanced cytotoxicity, improved pharmacokinetic properties, sustained release, and prolonged action of the PS. For continuous and reusable application, PS can be immobilized in polymers. Chemiluminescence, sonodynamic treatment, and radiofrequency irradiation allow to perform excitation of PS in the dark without external illumination, opening prospects for combating internal infections. Combination of PS with antibiotics can gain a synergistic effect, allowing in some cases to overcome the resistance of bacteria to antibiotics

Bioconversion of Airborne Methylamine by Immobilized Recombinant Amine Oxidase from the Thermotolerant Yeast Hansenula polymorpha

Aliphatic amines, including methylamine, are air-pollutants, due to their intensive use in industry and the natural degradation of proteins, amino acids, and other nitrogen-containing compounds in biological samples. It is necessary to develop systems for removal of methylamine from the air, since airborne methylamine has a negative effect on human health. The primary amine oxidase (primary amine : oxygen oxidoreductase (deaminating) or amine oxidase, AMO; EC 1.4.3.21), a copper-containing enzyme from the thermotolerant yeast Hansenula polymorpha which was overexpressed in baker’s yeast Saccharomyces cerevisiae, was tested for its ability to oxidize airborne methylamine. A continuous fluidized bed bioreactor (CFBR) was designed to enable bioconversion of airborne methylamine by AMO immobilized in calcium alginate (CA) beads. The results demonstrated that the bioreactor with immobilized AMO eliminates nearly 97% of the airborne methylamine. However, the enzymatic activity of AMO causes formation of formaldehyde. A two-step bioconversion process was therefore proposed. In the first step, airborne methylamine was fed into a CFBR which contained immobilized AMO. In the second step, the gas flow was passed through another CFBR, with alcohol oxidase from the yeast H. polymorpha immobilized in CA, in order to decompose the formaldehyde formed in the first step. The proposed system provided almost total elimination of the airborne methylamine and the formaldehyde

Special Issue “World of Biosensing”

The broad definition of the term biosensing relates to practically all processes of molecular recognition [...

Photodynamic Eradication of Trichophyton rubrum and Candida albicans

Conventional methods of onychomycosis treatment are ineffective in some cases because the cure of onychomycosis very often depends on the patient’s individual response to the treatment; therefore, there is a crucial need to research and develop new methods of onychomycosis therapy. One of the most innovative treatments is photodynamic therapy (PDT) using photosensitizers (PSs). However, effective treatment depends on the correct choice of photosensitizer and substances that improve the characteristics of the final formulation. The aim of our work was to find an effective formulation for the treatment of onychomycosis. To achieve this goal, we tested the effect of three types of PSs, rose Bengal (RB), malachite green oxalate (MGO), and methylene blue (MB), on Candida albicans. The most effective PS was RB, and so the study was continued with Trichophyton rubrum. Additional comparative studies were carried out on substances included in the formulation (urea and thiourea), focusing on their antifungal activity, which can improve penetration through the nail plate. The composition of the formulation that achieved 100% eradication of Trichophyton rubrum under our conditions consisted of 150 μM RB, 5% urea, and 0.5% thiourea in glycerol/water (70/30%, w/w) solution. A white luminescent lamp was used as a light source (1.9 ± 0.1 mW cm−2). Stability of the formulation was checked. The selected formulation shows potential for future simplification and acceleration of PDT treatment of onychomycosis

Polymer-Immobilized Photosensitizers for Continuous Eradication of Bacteria

The photosensitizers Rose Bengal (RB) and methylene blue (MB), when immobilized in polystyrene, were found to exhibit high antibacterial activity in a continuous regime. The photosensitizers were immobilized by dissolution in chloroform, together with polystyrene, with further evaporation of the solvent, yielding thin polymeric films. Shallow reservoirs, bottom-covered with these films, were used for constructing continuous-flow photoreactors for the eradication of Gram-positive Staphylococcus aureus, Gram-negative Escherichia coli and wastewater bacteria under illumination with visible white light using a luminescent lamp at a 1.8 mW·cm−2 fluence rate. The bacterial concentration decreased by two to five orders of magnitude in separate reactors with either immobilized RB or MB, as well as in three reactors connected in series, which contained one of the photosensitizers. Bacterial eradication reached more than five orders of magnitude in two reactors connected in series, where the first reactor contained immobilized RB and the second contained immobilized MB