The most reliable criterion for the microorganisms antibiotic susceptibility is the value of the minimum inhibitory concentration (MIC). The gradient diffusion method (epsilometric test, e-test), carried out using test strips impregnated with an antimicrobial agent, allows to obtain the quantitative value of MIC, bypassing the time-consuming steps of the traditional method of serial dilutions. We tested strips for the epsilometric test, developed at Saint-Petersburg Pasteur Institute. The quality control, carried by testing the reference strains of E. coli ATCC 25922 and S. aureus 29213, confirmed compliance of the manufacturer's declared antibiotic concentration ranges. The MIC values obtained in the study of the antibiotic susceptibility of 101 clinical isolates of microorganisms of the ESKAPE group, isolated from patients of various hospitals in St. Petersburg, were compared to 8 antimicrobial agents using tested test strips and the corresponding M.I.C. Evaluator of the Oxoid (UK). A high percentage of compliance of MIC values was demonstrated, as well as full compliance of susceptibility categories for all microorganism/antibiotic combinations. The resulting divergences in the MIC values did not exceed one step of a double serial dilution, which is permissible according to GOST R ISO 20776-1-2010. The study showed that the test strips developed at the Saint-Petersburg Pasteur Institute DNT are an acceptable alternative to import tests and, after the registration certificate will be completed, can be offered to determine the susceptibility of microorganisms to antimicrobial agents in bacteriological laboratories.
Keywords: E-test, minimum inhibitory concentration; ESKAPE; MIC; antimicrobial susceptibility testing; gradient diffusion method.