Acquiring of photosensitivity by Mycobacterium tuberculosis in vitro and inside infected macrophages is associated with accumulation of endogenous Zn–porphyrins

Abstract

Mycobacterium tuberculosis (Mtb) is able to transition into a dormant state, causing the latent state of tuberculosis. Dormant mycobacteria acquire resistance to all known antibacterial drugs and can survive in the human body for decades before becoming active. In the dormant forms of M. tuberculosis, the synthesis of porphyrins and its Zn-complexes significantly increased when 5-aminolevulinic acid (ALA) was added to the growth medium. Transcriptome analysis revealed an activation of 8 genes involved in the metabolism of tetrapyrroles during the Mtb transition into a dormant state, which may lead to the observed accumulation of free porphyrins. Dormant Mtb viability was reduced by more than 99.99% under illumination for 30 min (300 J/cm2) with 565 nm light that correspond for Zn–porphyrin and coproporphyrin absorptions. We did not observe any PDI effect in vitro using active bacteria grown without ALA. However, after accumulation of active cells in lung macrophages and their persistence within macrophages for several days in the presence of ALA, a significant sensitivity of active Mtb cells (ca. 99.99%) to light exposure was developed. These findings create a perspective for the treatment of latent and multidrug-resistant tuberculosis by the eradication of the pathogen in order to prevent recurrence of this disease.

Photoinactivation of <em>Mycobacterium tuberculosis</em> and <em>Mycobacterium smegmatis</em> by Near-Infrared Radiation Using a Trehalose-Conjugated Heptamethine Cyanine

“…Currently, methylene blue, radachlorin and various porphyrin derivatives are used as exogenously photosensitizers (PSs) for the inactivation of mycobacteria [5]. Mycobacterial cells with endogenously accumulated porphyrines also exhibited a great sensitivity to illumination [7][8][9]. Such PSs are activated by light with a wavelength not exceeding 690 nm, which prevents their widespread use for inactivating the pathogen in the deep tissues of the macroorganism.…”