Bacteriophages to Control Multi-Drug Resistant Enterococcus faecalis Infection of Dental Root Canals.

Phage therapy is an alternative treatment to antibiotics that can overcome multi-drug resistant bacteria. In this study, we aimed to isolate and characterize lytic bacteriophages targeted against Enterococcus faecalis isolated from root canal infections obtained from clinics at the Faculty of Dentistry, Ismalia, Egypt. Bacteriophage, vB_ZEFP, was isolated from concentrated wastewater collected from hospital sewage. Morphological and genomic analysis revealed that the phage belongs to the Podoviridae family with a linear double-stranded DNA genome, consisting of 18,454, with a G + C content of 32.8%. Host range analysis revealed the phage could infect 10 of 13 E. faecalis isolates exhibiting a range of antibiotic resistances recovered from infected root canals with efficiency of plating values above 0.5. One-step growth curves of this phage showed that it has a burst size of 110 PFU per infected cell, with a latent period of 10 min. The lytic activity of this phage against E. faecalis biofilms showed that the phage was able to control the growth of E. faecalis in vitro. Phage vB_ZEFP could also prevent ex-vivo E. faecalis root canal infection. These results suggest that phage vB_ZEFP has potential for application in phage therapy and specifically in the prevention of infection after root canal treatment.

Photochemical and thermal spiropyran (SP)-merocyanine (MC) interconversion: a dichotomy in dependence on viscosity.

The current study extends our work with spiropyran-merocyanines (SP-MC) as molecular photoswitches by delving into the effects of viscosity. This has led to the interesting finding of a dichotomy in viscosity dependence. Solutions of SP [6'-nitro-1,3,3-trimethylspiro(indolino-2,2'-benzopyran)] in a wide range of ethylene glycol-methanol (EG-MeOH) media (3.59 to 17.9 M in EG) were irradiated 90 s (365 nm). The absorbance at 90 s of MC (532 nm) formed photolytically varied with solvent. The least viscous medium yielded the highest concentration of MC and yields declined with increasing viscosity. Once irradiation ceased each system achieved thermal equilibrium. Molecular dynamics studies of typical thermal reactions governed by electronic and steric factors show that the transition state is achieved primarily after solvent reorganization has occurred to accommodate the new structure. It follows that in such thermal reactions viscosity may not cause any hindrance to the motion of atoms in molecules because solvent has already rearranged. In contrast, photochemical excitations occur at much higher rates (10(-15) s) than solvent reorganization, i.e. dielectric relaxation (10(-10) to 10(-12) s). The viscosity dependence of photochemical MC formation suggests that a major geometrical change is required for excited SP to be converted to MC. The dichotomy in dependence on viscosity is confirmed by the thermal equilibration of SP and MC. The equilibrium constant for the process increases three-fold (from 0.0535 to 0.158) as the EG content of the medium increases. However, the forward rate constant (SP → MC) is almost invariant with EG content or viscosity. The process is viscosity independent. The increase in the equilibrium constant with EG concentration is a result of a decline in the reverse rate constant for MC cyclisation to SP. This is attributed to special stabilisation of the MC that increases with increasing EG concentration. The present study, to our knowledge, is the first to dissect viscosity from solvent stabilisation factors in SP-MC systems. Further, the study highlights the fundamental difference between photolytic and thermal processes, providing another avenue of control for these SP-MC photoswitches.

Energy transfer in the azobenzene-naphthalene light harvesting system.

We have investigated the model light harvesting systems (LHSs) A and B typifying energy transfer (ET) between a naphthalene, Np (donor, D), and an azobenzene, Az (acceptor, A), shown schematically in Scheme 2 . These models were actualized as the naphthyl azo molecules 1 and 4 containing a methylene tether (Scheme 1). The methoxy azo molecules 2 and 5, respectively, served as benchmarks for the assessment of ET. Photophysical data, including initial rate constants for photoisomerization (trans to cis, t-1 --> c-1, and cis to trans, c-1 --> t-1), the relevant c-1 --> t-1 quantum yields, and fluorescence quenching with free naphthalene, 3, as D were measured. Therefore, (1) irradiation of 3 at (270 nm) to give 3* generates fluorescence at 340 nm that is 65% quenched by the trans isomer of 2 (t-2) and 15% quenched by c-2. Comparable naphthalenic fluorescence of c-1 (LH model A) is quenched beyond detectability. (2) Rates of photoisomerization were determined spectrophotometrically for c-1 --> t-1 starting from the c-1 photostationary state as compared with the c-2 --> t-2 benchmark. (3) Progressing toward more complex LH systems, the initial rate constants, k(i), for c-4 --> t-4 (LH model B), were measured as compared with the c-5 --> t-5 benchmark. (4) A new criterion for ET (D --> A) efficiency emerges that combines k(i) (c --> t) ratios and light absorption on irradiation (at 270 nm) ratios. On the basis of this new criterion, both 1 and 4 exhibit virtually quantitative ET efficiency. (5) Quenching data of 1 (almost complete) and 4 (95%) and ET are discussed by comparison with the relevant model azoarenes, 2 and 5, respectively, and in terms of geometrical considerations. Implications for the extension of the results, notably the new criterion for ET efficiency, in these LH models A and B to the polymer and block copolymer D-(CRR')(n)-A and D-(CRR')(n)-A-(CR''R''')(m)-D targets are considered.