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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., Competing Interests: The authors declare no conflict of interest.

Aim: To study main biologic characteristics of C. diphtheriae strains circulating in North-West Region of Russia for the last 15 years., Materials and Methods: Six hundred and fifty strains of C. diphtheriae isolated from ill persons and carriers in Saint-Petersburg, Leningrad region and Vologda region at various periods of time were studied. Identification of an infectious agent was performed according to methodic guidelines MU 4.2698-98. IHA-chromatographic test (ICS-test) on the basis of MKA, polymerase chain reaction, determination of adhesive activity and susceptibility to antibiotics were performed., Results: In recent years, circulation of C. diphtheriae strains with biologic characteristics similar to that observed in strains isolated during diphtheria epidemic and differed from that observed in strains isolated during the period of low incidence. Proportion of strains with "silent" gene between non-toxic in Elek-test C. diphtheriae increased. Decreasing of susceptibility to the range of antibiotics is observed in recent years., Conclusion: Revealed features of biologic characteristics of diphtheria agent circulating in post-epidemic period should be accounted during epidemiologic surveillance for diphtheria and choice of treatment of the infection.