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The search for new methods for identifying the pathogen in biological material, including microscopic, remains relevant. The study of ultrastructural changes of microorganisms as a result of exposure to various groups of antibiotics is important, because the morphology of the bacterial cell varies considerably depending on the conditions of cultivation. The purpose of the study: 1. To identify the nature of changes in the ultrastructure of preserved bacterial cells of S. aureus, cultivated in the presence of antibiotics. 2. To determine the viability of that part of the population of S. aureus, which remained exposed to suppressive concentrations of antibacterial drugs. 3. To determine whether the ultrastructural changes of the reference strain S. aureus ATCC 25923 in the proposed conditions completely reflect the nature of these changes for strains isolated from clinical material. Materials and methods. Three strains of S. aureus isolated from biological material and the reference strain S. aureus ATCC 25923 were used to investigate the S. aureus ultrastructure. The analysis was carried out on the basis of data obtained using scanning electron microscopy (SEM). In the process of sample preparation, the technique of imprinting bacteria from agarized nutrient medium was applied. Results and conclusions. The most common feature for the strains of clinical isolates of S. aureus was the formation of a large number of bacterial cells of a specific disc-shaped form in zones of influence of bacteriostatic antibiotics. In terms of the use of bactericidal drugs, part of the population remained spherical, the other part had irregular contours. Changes in the size of bacterial cells in growth suppression zones were multidirectional. Cultivation of bacteria under conditions of exposure to suppressive concentrations of antibacterial drugs stimulated the production of exocellular matrix. The ultrastructural changes of phenotypic variability of the reference strain S. aureus ATCC 25923 did not fully correspond to changes in the morphology of the bacterial cells of the strains of clinical isolates. The viability of bacteria remaining in the zones of growth suppression has been confirmed in all cases of antibiotic exposure, except gentamicin. Thus, the study revealed the nature of changes in the ultrastructure of S. aureus as manifestations of phenotypic variability of microorganisms in response to the presence of antibacterial drugs with different mechanisms of action.

Morphological Сhanges of S. Aureus Cultivated in the Presence of Antibacterial Drugs