In many countries around the world, massive declines in bee colonies have been reported as a consequence of the multifactorial effects of exogenous and endogenous factors. The development of opportunistic infections in bees is due to an imbalance of opportunistic pathogenic microflora that colonise the midgut of insects. The problem of dysbacteriosis in various animal species, including bees, is of interest to veterinarians. Therefore, the search for new remedies alternative to antibiotics is a high priority in beekeeping. Probiotic preparations have been proposed as new and safe medicines for the treatment and prevention of dysbacteriosis in human and veterinary medicine. Probiotics are products containing live micro-organisms that are able, in a certain dosage, to influence the macro-organism effectively. The application of such therapeutic additives to insects is preceded by their preliminary in vitro testing. Therefore, the main aim o the study was to determine the direction of action (bacteriostatic, bactericidal, antagonistic) of «EM® PROBIOTIC FOR BEES», diluted with sugar syrup solution and water in different concentrations, against Klebsiella pneumoniae, Klebsiella (Enterobacter) aerogenes bacteria and on mixed microbialas sociation in vitro. An in vitro experiment on the above probiotic agent was carried by diffusion in agar wells (well method) and a modified KirbyBauer method for the beekeeping industry (disk diffusion method). Bacteriostatic, bactericidal and antagonistic effects were determined visually and by measuring diameter of the are aaround the discs and wells. The bacteriostatic effect of probiotic microorganisms against enterobacteriaceae of Klebsiella pneumoniae species was recorded to be maintained at the same level when diluted with 50 % sugar syrup solution in concentrations from 0.5 % to 30 %. «EM® PROBIOTIC FOR BEES» diluted with water had pronounced antagonistic effect against Klebsiella pneumoniae bacteria by diffusion in agar wells method at concentrations of 0.5 % - 75,4±1,04 mm and 1% - 61,2±0,42 mm on the third day of the experiment. By diluting the probiotic with 50% sugar syrup solution, inhibition of the growth of Klebsiella (Enterobacter) aerogenes bacteria was observed in concentrations of up to 50%, ranging from 18,2±0,42 mm to 25,4±0,45 mm (disk diffusion method). Bactericidal effect of «EM® PROBIOTIC FOR BEES» diluted with water against mixed microbial association isolated from bee colonies with signs of intestinal disorders was observed at a concentration of 10% with a diameter of 18,6±0,57 mm by the disk diffusion method. Thus, «EM® PROBIOTIC FOR BEES» has antagonistic, bacteriostatic and bactericidal effects against enterobacteriaceae of bees Klebsiella pneumoniae, Klebsiella (Enterobacter) aerogenes species and agaist mixed microbial associations. The nature of the action of this probiotic depends on the solvent and its concentration, which in turn determines the direction and purpose of its application.

Key words: beekeeping, dysbiosis, Klebsiella (Enterobacter) aerogenes, Klebsiella pneumoniae, bactericidal and bacteriostatic effects, antagonistic action.