Stabilization of tigecycline solutions during susceptibility testing of microorganisms by broth microdilution method

Introduction. Tigecycline is widely used in the treatment of infections, leading to the emergence of resistant bacteria. Determining susceptibility by broth microdilution method is recommended to be conducted using freshly prepared Mueller–Hinton broth (MHB) or MHB with antioxidant additives, due to the oxidation of the antibiotic. At the same time, there is no information on the possibility of storing and further using antibiotic solutions. The aim of the study is to determine the feasibility of stabilizing and rationally using tigecycline solutions to achieve acceptable values of minimum inhibitory concentrations (MIC) when testing control strains by the reference method. Materials and methods. In the study, the MIC of tigecycline for Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, and Streptococcus pneumoniae ATCC 49619 was determined using the microdilution method in MHB, which was pre-prepared and stored for 24–48 hours prior to the study. For the study, a tigecycline stock solution was prepared in water with the addition of various concentrations of Оxyrase, which were stored at 2–6°C and –70°C, and then testing was conducted in accordance with GOST R ISO 20776-1-2022. Results. The stability of the tigecycline stock solutions does not exceed 5 hours at 2–6°C, but with the addition of 5.0–8.0% Оxyrase, it increases to 16 days, allowing for the determination of MIC values for all test strains within the acceptable range. Changing the storage temperature to –70°C increases the stability of the solutions to 43 days, and with the addition of 5.0–8.0% Оxyrase, to at least 48 weeks Conclusion. The possibility of stabilizing tigecycline solutions stored at negative temperatures (with and without the addition of Оxyrase) has been determined to obtain acceptable MIC values when determining the susceptibility of control strains to antimicrobial agents. The use of these solutions allowed for a reduction in testing costs through the rational use of the antibiotic.