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Bacterial ghosts are intact walls of bacterial cells that are relieved of their contents through pores formed by mild biological or chemical methods. Methodology for generating bacterial ghosts increases the safety of killed vaccines while maintaining their antigenicity through milder preparation procedures. Moreover, bacterial ghosts can simultaneously carry several antigens or plasmid DNAs encoding protein epitopes. In recent years, there has been a growing interest in the development of prototype vaccines and systems for delivery of biologically active substances based on bacterial ghosts. This review discusses the progress in the development of this type of medications over the last years. Various methods of obtaining bacterial ghosts, their advantages and limitations are considered. The phage-mediated lysis of bacteria, molecular manipulations with lysis genes, difficulties encountered in scaling the biotechnological production of bacterial ghosts, and ways to overcome them are described in detail. The use of bacterial ghosts as alternative killed vaccines, adjuvants, recombinant antigenic platform, carrier of plasmid DNA by the models of pathogens of particularly dangerous infections of bacterial etiology is investigated.

Live vaccines induce both cellular and humoral immunity and are cheap and easy to use. The induction of immunity is provided through the reproduction of the vaccine strain in the host body without the development of the disease, since the bacterium to which it is necessary to induce the immunity is characterized by reduced virulence (attenuation). The first generation of attenuated strains was chosen from a variety of spontaneous or physically, chemically and biologically induced mutants after virulence assessment. The rapid development of molecular genetics makes it possible to significantly reduce the time of pathogen attenuation via obtaining knockout mutants with genes selected by a researcher or by inserting “avirulence genes” into the genome. But, given that the methodological aspects of the design of avirulent strains are basically clarified, the absence of officially established criteria for assessing the hazard in regulatory documents hinders the determination of the degree of attenuation. In this regard, there is a need for changes in the procedure for accounting and storage of bacterial cultures, as well as regulation of the process of transferring plague pathogen avirulent strains from the 1st into the 3rd pathogenicity group for subsequent use in the vaccine preparations development. Thereat, the requirements to methodological aspects of the safe generation of attenuated Yersinia pestis strains and the criteria for testing the virulence loss should be maintained at high levels

The causative agent of plague, Yersinia pestis, is classified as pathogenicity (hazard) group I agent, which means that the work with “wild type” strains should be carried out in BSL-3 facilities. Y. pestis EV NIIEG is a Δpgm strain, allowing experimental studies to be carried out in BSL-2 laboratories. However, the disease and its progression elicited by such strain do not entirely mirror the infection observed with fully virulent strains. Residual virulence of Y. pestis EV NIIEG strain for mice can be increased under in vivo iron supplementation. The aim of the study was to optimize methodological approaches to modeling experimental plague in laboratory animals following administration of attenuated Δpgm Y. pestis strains with iron dextran. Materials and methods. Simulation of plague infection in outbred mice was carried out through subcutaneous inoculation of Y. pestis EV NIIEG strain with iron dextran supplementation. The animal condition was assessed on a daily basis. In the course of the experiment, the pathological presentation and bacterial content in organs of mice were evaluated. Results and discussion. Mice inoculated subcutaneously with Y. pestis EV NIIEG strain in the presence of iron dextran developed a bubonic plague that resulted in lethal outcome with pathological changes of internal organs, characteristic of plague infection. In case of daily administration of iron, LD50 of Y. pestis EV NNIEG strain for the mice significantly exceeded the same one with a single injection. Differences in the survival rate among animals in the groups with a single and multiple administration of iron compared to the control group were statistically valid. Thus, attenuated Δpgm Y. pestis strains in the presence of iron dextran can be used to model experimental plague in mice with marked pathological changes and lethality in BSL-2 laboratories.