Anthrax poses a pressing issue for veterinary medicine and public health in many countries, including the Russian Federation, which necessitates the improvement and development of new, sensitive and specific diagnostic tools.The aim of the work was to create an experimental peroxidase conjugate for the detection of specific antibodies to the anthrax pathogen and to optimize the conditions for performing enzyme immunoassay (ELISA).Materials and methods. The peroxidase conjugate was constructed using horseradish peroxidase and Staphylococcus aureus protein A (Sigma-Aldrich, USA). Bacterial antigens isolated from strains of Bacillus anthracis 55ΔTPA-1Spo, B. anthracis Sterne 34 F2 were used as sensitizing agents. The developed experimental batches of the conjugate were tested in ELISA for the ability to bind antibodies in the blood sera of anthrax patients and vaccinated individuals. The sensitivity, specificity, and accuracy of the method were calculated using the built-in functions of the ROCR software package.Results and discussion. The peroxidase conjugate to detect specific antibodies to the anthrax pathogen in the study of clinical material has been developed; conditions for the ELISA performance have been optimized. To interpret the results of the study, a threshold value of the positivity coefficient was used, below which the result was considered negative, and at an equal or higher value, positive. The test demonstrated significant differences in the “positivity coefficient” indicator for the “Healthy”/“Sick” and “Healthy”/“Vaccinated” groups, while the differences between the “Sick”/“Vaccinated” groups were statistically insignificant. The maximum accuracy of the method was observed at blood serum dilutions of 1:250 and 1:500. 100 % intra-run, run-to-run and series-to-series reproducibility has been established for all positive samples. The sensitivity and specificity of the experimental peroxidase conjugates were 100 and 95.8 %, respectively, and the accuracy was 97.6 %.
Liquid erythrocyte diagnostic preparations have a practical disadvantage; i.e., long-distance transportation involving possible non-compliance with cold-chain requirements may result in a complete loss of biological activity. A lyophilisation technology is necessary to ensure that the preparations retain their original properties for a long time. The aim of the work was to develop a protective medium and conditions for lyophilisation to stabilise the erythrocyte diagnostic preparation of tularaemia immunoglobulin. Materials and methods: Gelatin, thiourea, trehalose, sucrose, dextran, and Tween 80 were used as excipients for protective media. The authors used nine strains of homologous and heterologous microorganisms of different genera and species to control the lyophilised diagnostic preparation sensitivity and specificity. Evaluation of the main stability-related quality attributes (appearance of the dried preparation, loss on drying, solubility, appearance after reconstitution, appearance after settling, sensitivity, specificity) considered the temperatures specific to the climatic zones where the in vitro diagnostics is intended to be marketed and used. Results: The authors developed protective stabilising media with different compositions, used them in freeze-drying of the preparation and carried out control testing. The most promising was the lyophilisation medium containing a smaller amount of ingredients —6% of dextran, 0.06% of Tween 80 and up to 0.01% of sodium azide—as it was the simplest one to prepare and ensured complete preservation of the quality attributes. The authors carried out practical evaluation of lyophilisation procedures, and the 12–14-hour procedure proved to be the most cost-effective. Conclusions: The results of long-term, or real time, and accelerated stability testing of the lyophilised diagnostic preparation demonstrated the possibility of two-year storage at a labelled temperature of 2–8 °C, as well as at elevated and low temperatures of 30±2 °С and –18 °С, respectively. The tests showed no negative effects of the temperatures on the controlled quality attributes.
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