Introduction. Bacteria of the genus Staphylococcus are opportunistic microorganisms that have a high pathogenic potential, producing a number of aggression enzymes, which gives staphylococcus a priority opportunity to compete in microbiocenoses and, under certain conditions, cause infectious and inflammatory complications in patients. Patients with leukemia are no exception. Recently, probiotics have been widely used for prophylactic and therapeutic purposes. The use of probiotics to prevent dysbacteriosis and correct the composition of the microflora of biotopes in patients with leukemia is of great importance for the prevention and early diagnosis of infectious complications, which directly affects the targeted preventive and etiotropic treatment of these patients. The study of the influence of starter cultures of probiotics on the microflora of biotopes of patients with leukemia, including the pathogenic potential of staphylococci, which affects the risk of infectious and inflammatory complications, is relevant.

Aim. To investigate the effect of probiotic cultures on the pathogenic properties of staphylococci that were isolated from the mucous membranes of the nasal cavity and pharynx of patients with leukemia, in the dynamics of taking probiotics.

Materials and methods. The pathogenic properties of 29 strains of microorganisms of the genus Staphylococcus, which were isolated from the mucous membranes of the pharynx and nasal cavity of patients with leukemia, were studied in the dynamics of taking a bicomponent or multicomponent probiotic, which mainly included lacto- and bifidobacteria. The presence of the following aggression enzymes in staphylococci was determined: lecithinase, plasmacoagulase, phosphatase, hemolysins, fibrinolysin and lysozyme, according to generally accepted methods.

Results.  The presence of pathogenic properties was demonstrated in S. aureus and S. epidermidis strains isolated from the mucous membranes of the pharynx and nasal cavity of leukemia patients, ranging from 23 % to 100 %. Following the administration of probiotics, the isolated staphylococcal strains either lose or increase the synthesis of certain aggression factors. A positive outcome is the loss of ability to produce certain pathogenicity enzymes: for S. aureus: plasmacoagulase (19.0 % of strains) and fibrinolysin (9.6 %); for S. epidermidis: phosphatase (9.0 %) and fibrinolysin (19.2  %). This attenuates the virulence of staphylococci and can contribute to a reduction in the risk of staphylococcal-induced infectious and inflammatory complications in leukemia patients, subsequently having a beneficial impact on the course of these patients’ treatment.”

Conclusions. Pathogenic properties were demonstrated in strains of S. aureus and S. epidermidis isolated from the mucous membranes of the pharynx and nasal cavity of patients with leukemia, ranging from 23.1 % to 100 %. Against the background of probiotic use, the isolated staphylococcal strains lose or increase the synthesis of certain aggressive factors. A positive effect is the loss of the ability to produce certain pathogenicity enzymes: S. aureus – plasminogen activator (19.0 % of strains) and fibrinolysin (9.6 %), S. epidermidis – phosphatase (9.0 %) and fibrinolysin (19.2 %), which weakens the virulence of staphylococci and may contribute to reducing the risk of infectious and inflammatory complications of staphylococcal etiology in patients with leukemia and, as a result, have a positive effect on the course of treatment of these patients.

Keywords: leukemia, nasal cavity and pharynx, staphylococci, pathogenic properties, probiotics.