Several types of phototherapy target human pathogens and Porphyromonas gingivitis (Pg) in particular. The various approaches can be organized into five different treatment modes sorted by different power densities, interaction times, effective wavelengths and mechanisms of action. Mode 1: antimicrobial ultraviolet (aUV); mode 2: antimicrobial blue light (aBL); mode 3: antimicrobial selective photothermolysis (aSP); mode 4: antimicrobial vaporization; mode 5: antimicrobial photodynamic therapy (aPDT). This report reviews the literature to identify for each mode (a) the putative molecular mechanism of action; (b) the effective wavelength range and penetration depth; (c) selectivity; (d) in vitro outcomes; and (e) clinical trial/study outcomes as these elements apply to Porphyromonas gingivalis (Pg). The characteristics of each mode influence how each is translated into the clinic.

Whole-cell spectra of human pathogens are examined to identify species-specific wavelengths of maximum light absorption. It is presented how these data relate to clinical efficacy for antimicrobial phototherapies. Twelve species of microorganisms were cultured to exponential growth then processed and suspended in a scattering solution. Diffuse reflectance from the sample was delivered to two spectrometers that covered a spectral range of 370nm to 1200nm. Reflectance spectra were converted to relative absorbance. Absorbance spectra from multiple trials were averaged to produce a representative spectrum for each species. All pathogens studied demonstrated an absorbance spectrum with a primary component in the range 405-426 nm and 1-4 secondary components in the range 445-636 nm. Antibiotic-resistant and antibiotic-sensitive strains of Pseudomonas aeruginosa (Pa) had identical absorbance spectra. Whole-cell spectra support the hypothesis that a pathogen’s absorbance is directly related to efficacy of photoinactivation. The spectral signatures in all pigmented bacteria tested appear to be that of various combinations of in situ porphyrins. The knowledge of the absorption spectrum of a given pathogen provides a logical start for selecting the appropriate light source for a clinical trial.

The chicken brainstem sound localization neural network exhibits a case where fiber length varies continuously across the fiber arrays connecting n. magnocellularis and n. laminaris. Detailed morphometric measurements were taken to quantify these length gradients. For both ipsilateral and contralateral projections, the path lengths connecting the caudal low‐frequency segments are longer than those at the rostral high‐frequency end, with a linear path length gradient between them. The length and the length gradient of the contralateral projection increase from hatchling to 2–4 weeks. Synchronous transmission of information is achieved if there is a conduction velocity gradient across both the ipsilateral and contralateral fiber tracts. Adjustments of conduction velocity are required at both the cellular and population levels. A model is proposed that balances conduction distances and velocities by varying the number of nodes of Ranvier along a gradient to achieve isochronicity across the entire network. Continued differential growth between fiber arrays requires a continuous timing adjustment during development and maturation. Control is assigned to the oligodendrocytes that produce and maintain myelin.