[Cypopathic effect of diphtheria pathogen in the composition of biofilm.]

When the nasopharynx is colonized with toxigenic strains of the diphtheria pathogen, toxin is released, which contributes to the death of epithelial cells. But in bacterial carriers, the development of the clinical picture of the disease does not occur. This is due to the peculiarities of the state of their immune system, as well as the peculiarities of the production of diphtheria exotoxin by corynebacteria in the biofilm. Goal. Determining the nature of the cytopathic effect of C. diphtheriae as part of a biofilm in CHO-K1 cell culture. The planktonic and biofilm (120- and 720-hour) cultures of the strains were studied: C. diphtheriae gravis tox⁺ № 665, C. diphtheriae gravis tox⁺ № 6765, C. diphtheriae mitis tox⁺ № 269, C. diphtheriae gravis tox⁺ isolated from a patient with a diagnosis Localized oropharyngeal diphtheria C. diphtheriae gravis with a silent tox-gene. Biofilm (120- and 720-hour) cultures of diphtheria pathogen strains were obtained according to the Watnik method. The cytopathic effect of corynebacterial strains was studied on a CHO-K1 cell culture, taking into account in an inverted microscope. When studying the cytopathic effect of planktonic cultures of toxigenic strains of corynebacteria, it was found that the number of living CHO-K1 cells after 24 hours was insignificant (25.3±1.2%) and sharply decreased (2.5±0.5%) after 72 hours of cultivation. Under the influence of biofilm and, especially, 720-hour cultures, a different cytopathic effect dynamics was found: the number of living cells after 24 hours remained significant (82.5±2.2%), while at 72-hour it decreased to 25.0±3.0%. In the study of filtrates of planktonic and biofilm cultures of C. diphtheriae strain with a «silent» tox-gene, similar patterns were revealed. However, the number of live CHO-K1 cells when exposed to the filtrate of a 720-hour biofilm culture was significantly higher (p≤0.05) than when studying toxigenic strains of corynebacteria. Considering the nature of the cytopathic action, it was found that planktonic cultures of toxigenic strains of corynebacteria are characterized by a change in the cell monolayer, manifested by their thinning and elongation. The study of 720-hour biofilm cultures at 72-hour exposure revealed the appearance of a large number of rounded cells (63-69%). The cytopathic effect, formed under the influence of filtrates of planktonic and biofilm cultures of C. diphtheriae with a «silent» tox-gene, as well as strains of non-diphtheria corynebacteria, is characterized by rounding of cells and the formation of symplasts. In the biofilm, the intensity of the cytopathic effect of toxigenic C. diphtheriae strains and C. diphtheriae strain with a silent tox-gene decreased. CPD, manifested by thinning and lengthening of CHO-K1 cells, is associated with the action of diphtheria exotoxin, and rounding is associated with corynebacterial enzymes and, apparently, fragments of surface structures - adhesins. Decreased release of toxin and enzymes beyond the C. bihfilm matrix is a significant cause of the «asymptomatic» carriage of diphtheria.