INTERACTION OF ANTIMICROBIAL SUBSTANCES IN ESCHERICHIA COLI

The effectiveness of the combined antimicrobial drug primarily depends on the interaction of its active substances in the target species of microorganisms, which can be manifested in synergism, antagonism or indifference (additive effect). The guarantee of an effective clinical response of an animal suffering from a bacterial infection to the use of a combined drug is the synergism of its active pharmaceutical ingredients (API) with respect to a microorganism sensitive to their action, the causative agent of the disease. The article presents the results of the study of the interaction of various antimicrobial substances, which are the active substances of combined chemotherapeutic drugs present on the veterinary market of Ukraine, in Escherichia coli. The indications for the use of these drugs include the treatment of colibacteriosis, one of the most common bacterial zoonotic diseases in young farm animals. The study of the interaction of antimicrobial substances was carried out by the checkerboard method, based on the minimum inhibitory concentrations (MIC) of each API of the combination for Escherichia coli. The reference test microorganism Escherichia coli ATCC 11105 was used for the study. The interaction of oxytetracycline and neomycin caused an additive effect in Escherichia coli, when the result of the action of both substances is equal to the sum of the effects caused by each of the substances separately. The interaction of enrofloxacin and trimethoprim, enrofloxacin and gentamicin, enrofloxacin and colistin, doxycycline and colistin, and sulfadiazine and trimethoprim was manifested in synergism against Escherichia coli. In each case, the synergistic effect depends on various factors: the mechanisms of action of antimicrobial substances in combination directed at different target sites in the bacterial cell; the nature of their effect on the bacterium (act bactericidal or bacteriostatic); action in the same direction, as in the case of sulfadiazine and trimethoprim, when they compete for inhibition of different enzymatic stages of folate metabolism.