Staphylococcus aureus as a target of peripheral blood microbicidal factors from healthy donors

Objective. The aim of investigation was to evaluate the bacteriolytic activity of the peripheral blood of healthy donors against S. aureus. Currently, much attention is paid to the involvement of opportunistic microorganisms in the development of infectious and inflammatory diseases, among which one of the leading places is occupied by the processes of staphylococcal etiology. Staphylococcus aureus possesses a unique spectrum of pathogenic factors, which, together with intracellular persistence, allow staphylococci to avoid exposure to immune factors and other agents.

Materials and methods. The bacteriolytic activity of the peripheral blood of 32 healthy donors, as well as the ability of the whole blood and serum to destroy biofilms, were evaluated. The phagocytic activity of peripheral blood monocytes and neutrophils and the ability to produce hydroxyl radicals were analyzed. For opsonization of S. aureus, a commercial immunoglobulin G or donor serum was used.

Results. It was shown that the whole peripheral blood practically does not have a significant effect on the number of viable cells of S. aureus. However, freshly obtained blood serum significantly destroys the biofilm. It has been established that a fifth part of peripheral blood leukocytes is absorbed by S. aureus. After opsonization of microbial cells with immunoglobulin G, the indices of phagocytic activity of monocytes and neutrophils did not change significantly. When using freshly obtained serum for opsonization of objects, a stimulating effect on the production of hydroxyl radicals by leukocytes was revealed (2758.7 ± 725.3 and 870.6 ± 197.4 related light units, respectively; p < 0.05). After heating the serum at 56 °C, the stimulating effect was leveled (1091.1 ± 234.7 related light units; p > 0.05 for samples with non-opsonized objects). In general, the obtained data indicate that the complement components can be recognized as the most effective system for the elimination of S. aureus.

Conclusions. Thus, S. aureus uniquely adapted to the human body that allows staphylococci to persist for a long time without clinical manifestations. It can be assumed that among the factors of the immune system, the proteins of the complement system, which destroy both S. aureus cells and the biofilm matrix, probably have the most effective bactericidal action. However, the effectiveness of this system depends on the protein-synthesizing function of the liver, the availability of microorganisms to the action of complement.