Effect of Photodynamic Inactivation against Dormant Forms and Active Growing Cells of Mycobacterium smegmatis

A potential method for the destruction of dormant Mycobacterium smegmatis ( Msm ) mycobacteria via photodynamic inactivation (PDI) using their ability to store endogenous porphyrins during the transition to a dormant state was studied. The dormant Msm cells were obtained under gradual acidification of the growth medium in the stationary phase for 14 days at different concentrations of ferric ions and the presence of 5-aminolevulinic acid in the growth medium. Cells were exposed to light at a wavelength of 532 nm emitted by an LLD10 laser for 5–60 min. It was shown that an increase in the coproporphyrin concentration in M. smegmatis after 6 days of growth correlated with the onset of a decrease in metabolic activity in cells and the formation of ovoid dormant forms. The dormant bacteria were sensitive to PDI and were destroyed after 15–30 min of illumination, in contrast to active cells. In the presence of 5-aminolevulinic acid and an optimal concentration of ferric ions (0.5 mg/L), there was an increase in the production of uroporphyrin in both active and dormant mycobacteria, which was accompanied by an increase in sensitivity to the action of PDI. The results demonstrate the promise of PDI for the destruction of dormant mycobacteria and the fight against latent tuberculosis.