To develop a modern plague vaccine, we used hypo-endotoxic Yersinia pestis bacterial ghosts (BGs) with combinations of genes encoding the bacteriophage ɸX174 lysis-mediating protein E and/or holin-endolysin systems from λ or L-413C phages. Expression of the protein E gene resulted in the BGs that retained the shape of the original bacterium. Co-expression of this gene with genes coding for holin-endolysin system of the phage L-413C caused formation of structures resembling collapsed sacs. Such structures, which have lost their rigidity, were also formed as a result of the expression of only the L-413C holin-endolysin genes. A similar holin-endolysin system from phage λ containing mutated holin gene S and intact genes R-Rz coding for the endolysins caused generation of mixtures of BGs that had (i) practically preserved and (ii) completely lost their original rigidity. The addition of protein E to the work of this system shifted the equilibrium in the mixture towards the collapsed sacs. The collapse of the structure of BGs can be explained by endolysis of peptidoglycan sacculi. Immunizations of laboratory animals with the variants of BGs followed by infection with a wild-type Y. pestis strain showed that bacterial envelopes protected only cavies. BGs with maximally hydrolyzed peptidoglycan had a greater protectivity compared to BGs with a preserved peptidoglycan skeleton.

Background/Objectives: Yersinia pestis is an important zoonotic pathogen responsible for the rare but deadly disease of people with bubonic, septic, or pneumonic forms of plague. The emergence of multidrug-resistant Y. pestis strains has attracted more and more researchers’ attention to the search for molecular targets for antivirulence therapy, including anti-nutritional-virulence therapy. The glnALG operon plays a crucial role in regulating the nitrogen content within a bacterial cell. This operon codes for three genes: the structural gene glnA and the two regulatory genes glnL and glnG. In this study, we tested the effect of the deletion of glnA and glnALG on the pathogenic properties of Y. pestis. Methods: To assess the contribution of nitrogen metabolism to Y. pestis virulence, knockout mutants ΔglnA and ΔglnALG were constructed. The former was unable to synthesize glutamine, while the latter was not only defective in glutamine synthesis but also lacked the two-component sensor–transcriptional activator pair GlnL and GlnG, which could partially compensate for the decrease in intracellular glutamine concentrations by transporting it from the host or by catabolic reactions. For vaccine studies, immunized mice and guinea pigs were injected s.c. with 200 LD₁₀₀ of the wild-type Y. pestis strain. Results: A single knockout mutation in the glnA gene did not affect the virulence of Y. pestis in mice and guinea pigs. Knockout of the entire glnALG gene cluster was required for attenuation in these animals. The ΔglnALG strain of Y. pestis did not cause death in mice (LD₅₀ > 10⁵ CFU) and guinea pigs (LD₅₀ > 10⁷ CFU) when administered subcutaneously and provided 100% protection of animals when subsequently infected with 200 LD₁₀₀ of the Y. pestis virulent wild-type strain 231. Conclusions: Y. pestis, defective in both the glutamine synthetase GlnA and the two-component sensor–transcriptional activator pair GlnL-GlnG, completely lost virulence and provided potent protective immunity to mice and guinea pigs subsequently challenged with a wild-type Y. pestis strain, demonstrating the potential use of the glnALG operon as a new molecular target for developing a safe and efficient live plague vaccine.

The aim of this work was to determine the role of periplasmic chaperone SurA in the pathogenesis of bubonic and pneumonic plague. Yersinia pestis surA knoc

Background/Objectives: Yersinia pestis caused the three plague pandemics that claimed more than two hundred million human lives. There is still no vaccine that meets all WHO requirements, and many researchers continue to develop plague vaccines using various technological platforms. For example, researchers led by Roy Curtiss 3rd have developed a new approach to achieve controlled, delayed attenuation of bacterial pathogens. Mutants generated using this method were superior in protecting Y. pestis-infected mice immunized with strains generated using traditional gene knockout. However, further studies are needed to determine the safety and efficacy of these delayed-attenuated strains in other mammalian species in order to extrapolate on humans the data obtained in accordance with the FDA Animal Rule. In this study, we compared the role of delayed shutting down of the crp gene alone versus delayed silencing of the crp gene in combination with loss of the pPst plasmid or single crp knockout in the safety of mutants in mice and guinea pigs, as well as their ability to induce protective immunity in these two animal species. Methods: Three Y. pestis strains, a Δcrp mutant, a mutant with arabinose-dependent regulated crp expression (araC P_BAD crp) or araC P_BAD crp mutant cured of plasmid pPst, were derived from virulent wild-type strain 231. To evaluate the safety, outbred mice or guinea pigs were immunized subcutaneously with serial tenfold dilutions of mutated strains. For vaccine studies, immunized animals were subcutaneously challenged with 200 LD₁₀₀ of the wild-type Y. pestis strain. Results: The challenge caused the death of 100% of naïve animals in controls. The Y. pestis strain 231Δcrp was nonlethal in mice at a dose of 107 CFU. The LD₅₀ of 231Δcrp strain in guinea pigs increased at least by 107-fold compared to that of the wild-type strain. The LD50s of the 231P_BAD-crp mutant in mice and guinea pigs were approximately 104-fold and 107-fold higher than those of Y. pestis 231, respectively. The 231P_BAD-crp(pPst¯) strain did not cause death in mice (LD₅₀>10⁷ CFU) and guinea pigs (LD₅₀>10⁹ CFU) when administered subcutaneously and was capable of inducing intense protective immunity in both species of laboratory animals. Conclusions: Our research has shown once again the necessity of balance between safety and effectiveness demonstrating the feasibility of further investigation of crp mutants as promising candidate plague vaccines.

The goal of this study is to find out the effect of deletion of some genes encoding biogenesis of components of the outer membrane protein complex on the virulence of Yersinia pseudotuberculosis mutants. Materials and methods. Y. pseudotuberculosis surA, degP, bamB, and ompH mutants were generated by RedGam mutagenesis using suicide vectors. The constructed mutants were characterized by growth rate, sensitivity to antibiotics, bile salts, and sodium dodecyl sulfate, as well as to the bactericidal action of normal human serum. Total composition of the outer membrane proteins of the knockout mutants was determined by SDS-PAGE. The virulence of DsurA, DdegP, DbamB and DompH was studied after subcutaneous, intraperitoneal, or oral infection of mice. Results. It was found that BamB, OmpH and SurA proteins were necessary for maintaining the integrity of the Y. pseudotuberculosis cell membrane, SurA and BamB proteins are important for resistance to the bactericidal action of serum complement and a high degree of attenuation of Y. pseudotuberculosis strains with deleted surA, degP, bamB genes for outbred mice was revealed. Conclusion. The surA, degP, and bamB genes can be used as potential molecular targets for construction of Y. pseudotuberculosis vaccine strains.

The goal of this study is to identify the effect of deletion of some genes encoding biogenesis of outer membrane protein complex components on the virulenc