Experimental Adaptation of a strain of the plague microbe to lyophilization process

The use of lyophilization as a means of preserving commercial properties of the dried live plague vaccine is closely linked to a number ofresistant microbial cells surviving in the preparation after microbial population exposure to such stress action. Lyophilized live vaccine efficiency, even without violation of storage rules at low temperatures (4 ± 2 – 6 ± 2 оС), decreases gradually due to death of live cells of microorganisms forming the base of a vaccine. Aim: The aim of this study was to enhance resistance of the reference vaccine strain Yersinia pestis EV of NIIEG lineage to freeze-drying in vacuum (lyophilization) by different techniques: the use of lyophilization process per se as a selection factor, resistant clone selection from populations of strains which underwent single, double and triple lyophiliation, strain culturing at low temperatures (4 ± 2 – 6 ± 2 °С). Summary and conclusion: It was demonstrated that after double and triple lyophilization the Y. pestis EV strain resistance to the process increased by 3–3.5 times. Clonal selection of twice and three times lyophilized variant facilitated detection of resistant clones and stabilization of this property.The clones selected were characterized by increased immunogenicity, high heat stability, as well as by increased duration of vaccine efficiency (by 2.3 times). A psychrophilic variant of Y. pestis EV strain was obtained in vitro acquiring higher resistance to lyophilization (in 2 times or more) in comparison with the reference strain. The number of psychrophilic variant cells surviving post-liophilization was higher in comparison with the commercial strain. Thus the methods used in this study for selection of strains and clones with the highest resistance to lyophilization from Y. pestis EV reference strain population showed a significant potential for quality improvement of dried live plague vaccine. So, the possibility of receiving of a vaccine of more high quality by means of the ways of selection explained in our work is experimentally confirmed. Effectiveness of these ways creates prerequisites for their use in production of a live plague vaccine.