Intra- and interspecies relatedness ofYersinia pestis by DNA hybridization and its relationship toYersinia pseudotuberculosis

The biochemical characteristics ofYersinia pestis are presented and compared with those ofY. pseudotuberculosis. Motility at 28°C, urease, fermentation of rhamnose, and growth rate on nutrient agar are the best means of separating these organisms. DNA hybridization studies demonstrated thatY. pestis strains are 90% or more interrelated and thatY. pestis andY. pseudotuberculosis are indistinguishable by DNA relatedness. On the basis of DNA data and biochemical and antigenic similarity, these organisms should be treated as two separate subspecies of the same species.Y. pseudotuberculosis was described beforeY. pestis and therefore has priority.Y. pseudotuberculosis subsp.pseudotuberculosis andY. pseudotuberculosis subsp.pestis are recommended as new designations forY. pseudotuberculosis andY. pestis. For medical purposes,Y. pestis andY. pseudotuberculosis can and should continue to be used.     

A new isolation medium for the revovery ofYersinia enterocolitica from environmental sources

Yersinia enterocolitica has been isolated from a wide variety of sources throughout the world. The isolation of this organism requires special awareness from bacteriologists. To ease this procedure, we have developed a new isolation medium—BABY 4—meant to be used for environmental studies. Compared with previously recommended media, such as SS agar, SS-D agar, and urea-novobiocin agar, it allows easy detection ofY. enterocolitica in various types of waters. It counterselects Enterobacteriaceae species fromY. enterocolitica in a ratio of 10^–1 to 10^–5 and makes quantitative studies of environmental sources possible. This medium also allows the detection after 3–4 days' incubation of as few as 10³ Y. enterocolitica per gram of stool.     

Homology models of the Yersinia pseudotuberculosis and Yersinia pestis general porins and comparative analysis of their functional and antigenic regions

The amino acid sequences of the Yersinia pseudotuberculosis porin (YPS) and Y. pestis porin (YPT) have recently deduced but their three-dimensional structures were not known. These sequences were analyzed using the servers 3D-PSSM and PredPort. The YPS and YPT porins were shown to have a high degree of identity (above 50%) in primary and secondary structures. The three-dimensional models of the Yersinia pseudotuberculosis porin (YPS) and Y. pestis porin (YPT) were obtained using the homology modeling approach, SWISS-MODEL Protein Modeling Server and 3-D structure of PhoE porin from E. coli as template. The superposition of the Calpha-atoms of the monomers of the Yersinia porins and PhoE porin gave a root mean square deviations of 0.47 A and 0.43 A for YPS and YPT respectively. Yersinia porins were found to be very similar in their three-dimensional structure to other non-specific enterobacterial porins, having the same features of overall fold and disposition of loop L3. The intrinsic structures of the monomer pores of YPS and YPT were investigated and their conductances were predicted with the program HOLE. The good correspondence between the theoretical and experimental magnitudes of YPS conductance was found. The Yersinia porins were determined to be unusual in containing the substitution, Glu replaced by Val, in a highly conserved pentapeptide (Pro-Glu-Phe-Gly-Gly-Asp), located in the loop L3 tip that disturbs the functionally important cluster of the acidic amino acids in the constriction site. Comparative analysis of structural organization of YPS and E. coli OmpF porin in the regions involved in subunit association and pore lumen was performed. The YPS porin functional properties were predicted. The differences between these porins in polar interactions playing a significant role in stabilization of the porin trimers were found and discussed in term of the variations in trimer stability. The Yersinia porins were shown to have the highest degree of the structural similarity. The differences between the porins were observed in their external loops. Their loops L6 and loops L8 showed 71.4 and 52.9% of sequence identity, respectively. The arrangement of charged residues clustered in the channel external vestibule of these porins was found to be also different suggesting the possible differences in their functional properties. The surface exposed regions of Yersinia porins involved in their potential sequential antigenic determinants were compared. The structural basis of their cross reactivity and antigenic differences is discussed.     

Update on: Shigella new serogroups/serotypes and their antimicrobial resistance

Shigellosis represents a major burden of disease in developing countries. A low infectious dose allows the disease to be spread effectively. Although shigellosis is mostly a self‐limiting disease, antibiotics are recommended to reduce deaths, disease symptoms and organism‐shedding time. However, in India, antimicrobial resistance among the genus Shigella is more common than among any other enteric bacteria. Notably, new serotypes or subserotypes in Shigella are reported from various parts of the world. Identification of new subserotypes of Shigella spp. is becoming a major issue as these strains are nontypeable by conventional serotyping. The commercially available antisera may not cover all possible epitopes of the O lipopolysaccharide antigen of Shigella serotypes. Therefore, molecular methods which most closely approach the resolution of full serotyping are necessary to identify such strains. In addition, the knowledge of a prevalent serotype in various geographic regions may assist in formulating strategies such as the development of a vaccine to prevent infection especially when the immunity to disease is serotype specific, and to understand the disease burden caused by new Shigella serotypes.     

Toggles and oscillators: new genetic circuit designs

Two recent papers report the de novo design of a functioning biological circuit using well-characterized genetic elements.(1,2) Gardner et al. designed and constructed a genetic toggle switch while Elowitz and Leibler built an oscillating genetic circuit. Both circuits were designed with the aid of mathematical models. These papers demonstrate progress towards the unification of theory and experiment in the study of genetic circuits. Comparison of the predicted and observed behavior of the circuits, however, shows that the models explain only some of the circuits' properties. Further study of the observed behaviors not predicted by the model would lead to new insight into the properties of genetic networks. BioEssays 22:507-509, 2000.     

Yersinia pseudotuberculosis plasmids and their significance in the realization of the epidemic process in pseudotuberculosis

The results obtained in the electrophoretic study of the plasmid spectra of 190 Y. pseudotuberculosis strains, isolated from different sources, in 0.6% agarose gel are presented. 11 types of plasmids differing in their molecular weight have been detected. Plasmids with a molecular weight of 45 MD determine Ca2+ dependence, bacterial virulence for white mice and autoagglutination. The presence of differences in Y. pseudotuberculosis strains of serovars I, III and IV has been established, which is manifested by their differing plasmid spectra. The relationship between the presence of plasmids with a molecular weight of 75 and 45 DM in the strains and the character of pseudotuberculosis morbidity in the population has been demonstrated. The epidemic course of infection correlates with the presence of both these plasmids and the sporadic course of infection, with the presence of the plasmid with a molecular weight of 45 MD only.     

Components of the outer membrane of Yersinia pseudotuberculosis and their role in the pathogenesis of pseudotuberculosis

The pore-forming protein, lipopolysaccharide-protein complex and lipopolysaccharide of Y. pseudotuberculosis outer membrane have been shown to participate in the penetration of the bacteria into the cells of the macroorganism, to produce a toxic effect on these cells and to enhance the ingesting activity of macrophages in small doses, while suppressing it in large doses. When introduced parenterally, protein induces a more pronounced clinical picture of specific reactive hepatitis in experimental animals and greater changes in their kidneys than the lipopolysaccharide--protein complex.     

Analysis of the plasmid composition of Yersinia pseudotuberculosis strains and its use for typing pseudotuberculosis pathogens

Electrophoresis in agarose gel has been used to study the plasmid spectra of 854 Yersinia pseudotuberculosis strains isolated from different sources. The plasmids found in the microbial strains are represented by the elements with molecular masses 82; 57; 45; 5.5; 4.4; 3.5; 2.7; 2.4; 2.3 Md. The variable spectra of plasmids is peculiar only for serovar I of Yersinia pseudotuberculosis. Plasmids p45 and p82 are classified as the main, while other plasmids as auxiliary ones. In accord with the classification all plasmid containing strains are divided into 8 plasmid strains. Using the proposed method for intraspecific typing of Yersinia pseudotuberculosis permits one to perfect the epidemiological analysis of pseudotuberculosis infection and make concrete the direction of prophylactic and antiepidemic measures.     

Enterotoxic activity of the pseudotuberculosis microbe

For the first time the activity of Y. pseudotuberculosis, its extracellular, surface antigen and Westphal's lipolysaccharide has been studied with the use of biological models (the ligated loop of the small intestine of a rabbit, the pulmonary model, the intradermal tests). This microorganism has been found capable of inducing the accumulation of exudate in the ligated loop of the small intestine of a rabbit and interfering with the permeability of the vascular walls. The toxic action of Y. pseudotuberculosis is neutralized by immunization.     

Presence of skin permeability factors in the extracellular products ofYersinia ruckeri

In this study we have demonstrated the presence of permeability factors (PF) in the extracellular products (ECP) of 16 strains of the bacterial fish pathogenYersinia ruckeri. The production and detection of these factors were dependent on the growth media and the ECP extraction procedure. The best results were obtained with a cellophane plate method and use of brain-heart infusion agar (BHIA) medium. The loss of necrotizing activity after heating the samples at 80°C for 15 min indicates the thermolabile nature of the toxin. In addition, this activity was not correlated with the production of hemolysins and cytotoxins by theY. ruckeri strains.     

A new index of interspecific competition for replacement and additive designs

The literature is reviewed to summarize the major indices of interspecific competition used in De Wit replacement experiments. Of the many indices that have been defined, some are less than clear as to their meaning, so interpretations are often difficult to make. In an effort to explore the performance of individual indices and to permit cross-correlation among indices, a series of hypothetical results in different competition scenarios is created. A standardized notation for all indices is also provided, along with equations and proofs. Nine indices are reviewed and analyzed for their behavior under the hypothetical scenarios and a new index that provides increased clarification and interpretability over other indices is proposed. Relative Yield Total, Aggressivity, and Relative Replacement Rate were shown to be poor measures of competition. Relative Crowding Coefficient has many restrictions to its use. The clearest index that includes two or more species is Relative Yield of Mixture. Indices that describe single species accurately were found to be Relative Yield (RY) and Relative Competition Intensity (RCI), both of which are mathematically convertible. An index introduced here, Change in Contribution (CC), is a single species index that differs from RY and RCI because it takes into account the overall biomass each species contributes.     

Increase of the antimicrobial susceptibility ofYersinia enterocolitica associated with the expression of the virulence plasmid

Virulent strains ofYersinia enterocolitica incubated in RPMI 1640 medium with 25 mM HEPES at 37°C were more susceptible to several antibiotics than their plasmid-free isogenic derivatives. The enumeration of viable bacteria in RPMI 1640 agar at 37°C to discriminate between plasmid-bearing and spontaneously derived, plasmid-free bacteria made it possible to show that the plasmid presence was associated with a fourfold decrease of minimal inhibitory concentration of ampicillin, streptomycin, gentamicin, chloramphenicol, and oxytetracycline. SinceY. enterocolitica is an intracellular pathogen and RPMI 1640 medium mimics the intracellular milieu, the plasmid-associated increase of susceptibility to antibiotics that are concentrated by animal cells may be of clinical relevance.