On the possibility of photodynamic inactivation of tracheobronchial tree pathogenic microbiota using methylene blue (in vitro study)

•Methylene blue retains its optico-physical properties in the range of 1–30 μM.•The photodegradation of methylene blue molecules at irradiation doses up to 30 J/cm2 does not exceed 30%.•Methylene blue provides effective inactivation of isolated Gram-positive and Gram-negative bacteria, including multi- and panresistant to antibiotics. The treatment of patients after mechanical ventilation of lungs suffering from a multi-species infection of the tracheobronchial tree can be complicated.. The situation is aggravated in patients with post-intubation tracheal stenosis, where infection plays a leading pathogenetic role in damage to the tracheal wall. As a result of such a pathological process, cicatricial stenosis of the trachea of purulent-inflammatory infectious genesis or infected tracheal stenosis (ITS) may occur. In this work, we studied the possibility of photodynamic inactivation of pathogenic microbiota typical for patients with ITS using methylene blue (MB) as a photosensitizer. 13 clinical isolates of 8 species of bacteria from 9 patients were susceptible to photodynamic inactivation with MB. 30 μM of MB at a light irradiation dose of 25 J/cm2 and incubation with MB for 15 min allows to completely inactivate bacteria found in the tracheobronchial secretions of patients with ITS. MB retains its optico-physical properties in the range of 3–30 μM and provides effective inactivation of isolated Gram-positive and Gram-negative bacteria, including multi- and pan-resistant to antibiotics.