Immunogenicity of Yersinia pestis grown on nutrient media at 28 and 37 degrees C

The immunogenicity of Y. pestis strain EV, grown in yeast-casein medium, yeast medium with Hottinger digest and yeast medium with sunflower-seed protein at 28 degrees C and 37 degrees C, for guinea pigs and white mice has been studied. As revealed in this study, these media ensure the formation of highly immunogenic populations of Y. pestis strain EV and, therefore, can be used for growing Y. pestis vaccine strains. Considerable fluctuations in the content of such highly protective antigen as fraction 1 do not affect the immunogenicity of live cultures of Y. pestis strain EV. This is due to the leveling of differences in the content of this antigen in the process of the multiplication of these bacteria in laboratory animals.     

The mutagenic effect of polymorphonuclear leukocytes on Yersinia pestis

As the result of in vitro experiments, Y. pestis auxotrophic mutants have been obtained under the influence of polymorphonuclear lymphocytes obtained from guinea pigs, previously immunized with Y. pestis strain EV. The mutagenic effect has been found to occur at minute 45 of phagocytosis. The control treatment of the bacteria with the lysate of neutrophils, homologous serum, penicillin (antibiotic-influenced selection) has not been found to lead to the appearance of auxotrophicity. These data suggest that the polymorphonuclear leukocytes of animals, having a set of powerful cytocidal systems, play an active role in the process of the natural variability of Y. pestis.     

The effect of different Yersinia pestis antigens on the cellular link in immunity

Immunization with live plague vaccine has been shown to give no protection to thymectomized mice from subcutaneous challenge with Y. pestis virulent strain. Under the action of the vaccine or individual Y. pestis antigens (fraction I) the functional and morphological activation of thymocytes and macrophages is observed, more pronounced in C57BL/6 mice and less pronounced in CBA mice. Y. pestis antigenic preparations (fractions I and II, pesticin) act as T-cell mitogens and are thus capable of inducing the in vitro proliferation of thymocytes. At the same time the in vivo action of fraction II induces a decrease in the level of lymphocytes in the peripheral blood of mice and the destruction of lymphocytes in their thymus and spleen.     

Quorum-sensing signal synthesis by the Yersinia pestis acyl-homoserine lactone synthase YspI

The acyl-homoserine lactone molecular species (AHLs) produced by the Yersinia pestis AHL synthase YspI were identified by biochemical and physical/chemical techniques. Bioassays of extracts from culture supernatants of the recombinant YspI and wild-type Yersinia pestis showed similar profiles of AHLs. Analysis by liquid chromatography-mass spectrometry revealed that the predominant AHLs were N-3-oxooctanoyl-L-homoserine lactone and N-3-oxo-hexanoyl-L-homoserine lactone.     

Transport of basic amino acids into Yersinia pestis cells

The transport of the basic amino-acids into the plague microbe cells has been shown to proceed by means of two transfer systems, the common transfer system and the system specific for lysine. Besides that, arginine can be transported into the plague microbe cells by the histidine transport system. The vaccine strain EV NIIEG was used as a model to study the amino-acid transport systems.     

The effect of Mg 2+ ions on the properties of various strains of Yersinia pestis

The strains of Yersinia pestis that restrict their growth on the media deficient for Mg2+ ions at 37 degrees C have been found. The bacterial cell lysis is registered under these conditions. The effect of Yersinia pestis own plasmids on the level of growth restriction in the absence of Mg2+ ions has been studied. The phenomenon is not connected with the presence of the plasmid determining Ca2(+)-dependence. The presence of 6Md plasmid coding for pesticinogenicity increased the frequency of colony formation, while the heavy plasmid determining the production of "mouse" toxin favoured the increase in growth restriction on Mg2(+)-less media. The clones growing under the latter conditions acquire the rearrangements in the DNA of the plasmid coding for the "mouse" toxin.     

The tissue heterogeneity of mononuclear phagocyte system cells interacting with Yersinia pestis

The work deals with the determination of the heterogeneity of cells of the mononuclear phagocyte system, localized in different tissues, in their interaction with Y. pestis. The macrophage populations under study have been found to be heterogeneous in their phagocytic activity with respect to Y. pestis. The digestive activity of alveolar macrophages is considerably lower than that of macrophages localized in other tissues. Macrophages obtained from different tissue are heterogeneous also in the intensity of changes in oxygen-dependent metabolic processes during their contacts with Y. pestis. Alveolar macrophages are less active in this respect than peritoneal ones. Alveolar macrophages under study have been shown to have their own characteristic features; for this reason, the data obtained in the study of one of these populations should not be extrapolated to other populations.     

pH6 antigen of Yersinia pestis interacts with plasma lipoproteins and cell membranes

The bacterial pathogen Yersinia pestis expresses a potential adhesin, the pH6 antigen (pH6-Ag), which appears as fimbria-like structures after exposure of the bacteria to low pH. pH6-Ag was previously shown to agglutinate erythrocytes and to bind to certain galactocerebrosides. We demonstrate that purified pH6-Ag selectively binds to apolipoprotein B (apoB)-containing lipoproteins in human plasma, mainly LDL. Binding was not prevented by antibodies to apoB. pH6-Ag interacted also with liposomes and with a lipid emulsion, indicating that the lipid moiety of the lipoprotein was responsible for the interaction. Both apoB-containing lipoproteins and liposomes prevented binding of pH6-Ag to THP-I monocyte-derived macrophages as well as pH6-Ag-mediated agglutination of erythrocytes. Binding of pH6-Ag to macrophages was not dependent on the presence of LDL receptors. Treatment of the cells with Triton X-100 or with methyl-beta-cyclodextrin indicated that the binding of pH6-Ag was partly dependent on lipid rafts. We suggest that interaction of pH6-Ag with apoB-containing lipoproteins could be of importance for the establishment of Y. pestis infections. Binding of lipoproteins to the bacterial surface could prevent recognition of the pathogen by the host defence systems. This might be important for the ability of the pathogen to replicate in the susceptible host.     

鼠疫菌毒力调控研究

鼠疫菌通过一系列转录调控子(如CRP、PhoP、RovA和Fur)控制着一些关键毒力因子(如Pla、强毒力岛、III型分泌系统等)的基因表达。鼠疫菌可感应宿主体内信号刺激,紧密调控毒力因子的表达。在这个紧密调控过程中,调控子、毒力相关基因构成了一个动态网络。鼠疫菌在从假结核菌祖先演化的进程中,基因表达调控网络的重塑在鼠疫菌毒力进化过程中发挥着不可取代的作用。     

Survival of Yersinia pestis on environmental surfaces

The survival of two strains of Yersinia pestis (avirulent A1122 and virulent Harbin) on the surfaces of four materials was investigated. Viability was evaluated with epifluorescence microscopy by using the metabolic stain cyanoditolyl tetrazolium chloride and plate counts. Small numbers of cells suspended in phosphate buffer survived 2 to 4 h after visible drying on stainless steel, polyethylene, or glass and beyond 48 h on paper. Cells suspended in brain heart infusion broth (BHI) persisted more than 72 h on stainless steel, polyethylene, and glass. Small numbers of cells suspended in BHI were still viable at 120 h on paper. These data suggest that Y. pestis maintains viability for extended periods (last measured at 5 days) under controlled conditions.     

The effect of Yersinia pestis EV76 6 MD plasmid on the composition of outer membrane proteins of Yersinia pseudotuberculosis YPIII]

On the basis of Yersinia pseudotuberculosis strain YPIII the isogenic variants containing the different combinations of 47 Md plasmids from Yersinia pestis or Yersinia pseudotuberculosis cells with the 6 Md pYP plasmid from Yersinia pestis EV (intact or having impaired the pla gene determining the synthesis of plasmocoagulase). The degradation of the secreted proteins encoded by the 47 Md plasmids of Yersinia pestis and Yersinia pseudotuberculosis in the cells harbouring the 6Md pYP plasmid has been registered. Yersinia pseudotuberculosis strain YPIII carrying its own 47Md and pYP plasmids also contained no YOP1 protein, in contract to the parent strain. The damage of the pla gene eliminated the destructive effect on the outer membrane proteins. Imposition of the 47Md and 6Md plasmids from Yersinia pestis in Yersinia pseudotuberculosis cells may be used for obtaining and study of the physiological role of low molecular mass proteins resulting from proteolysis of proteins encoded by the 47Md virulence plasmid of Yersinia.     

Survival of Yersinia pestis on Environmental Surfaces

The survival of two strains of Yersinia pestis (avirulent A1122 and virulent Harbin) on the surfaces of four materials was investigated. Viability was evaluated with epifluorescence microscopy by using the metabolic stain cyanoditolyl tetrazolium chloride and plate counts. Small numbers of cells suspended in phosphate buffer survived 2 to 4 h after visible drying on stainless steel, polyethylene, or glass and beyond 48 h on paper. Cells suspended in brain heart infusion broth (BHI) persisted more than 72 h on stainless steel, polyethylene, and glass. Small numbers of cells suspended in BHI were still viable at 120 h on paper. These data suggest that Y. pestis maintains viability for extended periods (last measured at 5 days) under controlled conditions.     

The evolution of flea-borne transmission in Yersinia pestis

Transmission by fleabite is a recent evolutionary adaptation that distinguishes Yersinia pestis, the agent of plague, from Yersinia pseudotuberculosis and all other enteric bacteria. The very close genetic relationship between Y. pestis and Y. pseudotuberculosis indicates that just a few discrete genetic changes were sufficient to give rise to flea-borne transmission. Y. pestis exhibits a distinct infection phenotype in its flea vector, and a transmissible infection depends on genes that are specifically required in the flea, but not the mammal. Transmission factors identified to date suggest that the rapid evolutionary transition of Y. pestis to flea-borne transmission within the last 1,500 to 20,000 years involved at least three steps: acquisition of the two Y. pestis-specific plasmids by horizontal gene transfer; and recruitment of endogenous chromosomal genes for new functions. Perhaps reflective of the recent adaptation, transmission of Y. pestis by fleas is inefficient, and this likely imposed selective pressure favoring the evolution of increased virulence in this pathogen.     

The response regulator PhoP negatively regulates Yersinia pseudotuberculosis and Yersinia pestis biofilms

A few Yersinia pseudotuberculosis strains form biofilms on the head of the nematode Caenorhabditis elegans , but numerous others do not. We show that a widely used Y. pseudotuberculosis strain, YPIII, is biofilm positive because of a mutation in phoP , which encodes the response regulator of a two-component system. For two wild-type Y. pseudotuberculosis that do not make biofilms on C. elegans , deletion of phoP was sufficient to produce robust biofilms. In Yersinia pestis , a phoP mutant made more extensive biofilms in vitro than did the wild type. Expression of HmsT, a diguanylate cyclase that positively regulates biofilms, is diminished in Y. pseudotuberculosis strains with functional PhoP.