Toxoplasmosis, caused by an intracellular protozoan parasite, Toxoplasma gondii, is widespread throughout the world. The disease is of major medical and veterinary importance, being a cause of congenital disease and abortion in humans and domestic animals. In addition, recently it has gained importance owing to toxoplasma encephalitis in AIDS patients. In the last few years, there has been considerable progress towards the development of a vaccine for toxoplasmosis, and a vaccine based on the live-attenuated S48 strain was developed for veterinary uses. However, this vaccine is expensive, causes side effects and has a short shelf life. Furthermore, this vaccine may revert to a pathogenic strain and, therefore, is not suitable for human use. Various experimental studies have shown that it may be possible to develop a vaccine against human toxoplasmosis. Recent progress in knowledge of the protective immune response generated by T. gondii and the current status of development of a vaccine for toxoplasmosis are highlighted.

Toxoplasma gondii SAG1, GRA1, and GRA7 recombinant antigens may be regarded as tools for the detection of T. gondii immunoglobulin G antibodies in persons with chronic and acute toxoplasmosis. GRA7 is more correlated with acute toxoplasmosis. A combination of these antigens will increase the sensitivity of enzymelinked immunosorbent assays.

Single-stranded-DNA-binding proteins (SSBs) play essential roles in DNA replication, recombination and repair in bacteria, archaea and eukarya. This paper reports the identification and characterization of the SSB-like proteins of the thermophilic bacteria Thermus thermophilus and Thermus aquaticus. These proteins (TthSSB and TaqSSB), in contrast to their known counterparts from mesophilic bacteria, archaea and eukarya, are homodimers, and each monomer contains two ssDNA-binding domains with a conserved OB (oligonucleotide/oligosaccharide-binding) fold, as deduced from the sequence analysis. The N-terminal domain is located in the region from amino acid 1 to 123 and the C-terminal domain is located between amino acids 124 and 264 or 266 in TthSSB and TaqSSB, respectively. Purified TthSSB or TaqSSB binds only to ssDNA and with high affinity. The binding site size for TaqSSB and TthSSB protein corresponds to 30-35 nucleotides. It is concluded that the SSBs of thermophilic and mesophilic bacteria, archaea and eukarya share a common core ssDNA-binding domain. This ssDNA-binding domain was presumably present in the common ancestor to all three major branches of life.

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In search of an effective DNA typing technique for hospital epidemiology use, the performance and convenience of a PCR melting profile (PCR MP) technique based on using low denaturation temperatures during ligation-mediated PCR (LM PCR) of bacterial DNA was tested. A number of Escherichia coli isolates from patients of the Clinical Hospital in Gdańsk, Poland, were examined. We found that the PCR MP technique is a rapid method that offers good discriminatory power and excellent reproducibility and may be applied for epidemiological studies. The usefulness of the PCR MP for molecular typing was compared with the pulsedfield gel electrophoresis method, which is currently considered the gold standard for epidemiological studies of isolates recovered from patients and the environment. Clustering of PCR MP fingerprinting data matched pulsed-field gel electrophoresis data. The features of the PCR MP technique are discussed in comparison with conventional methods. Data presented here demonstrate the complexity of the epidemiological situation concerning E. coli that may occur in a hospital.Over the past 20 years, a significant number of DNA-based techniques have been introduced into the field of bacterial characterization and taxonomy. These genomic fingerprinting methods were developed to detect DNA sequence polymorphisms by using general principles, such as restriction endonuclease analysis, molecular hybridization, and PCR amplification. DNA fingerprinting involves the display of a set of DNA fragments from a specific DNA sample. A variety of DNA fingerprinting techniques are presently available (1-7, 11-13), most of which use PCR for detection of fragments. The choice of fingerprinting technique depends on the type of application. Ideally, a fingerprinting technique should require no prior investments in terms of sequence analysis, primer synthesis, or characterization of DNA probes. A number of fingerprinting methods which meet these requirements have been developed. The fingerprints are obtained by visualizing many parts of the genome. Differences in these fingerprints between individuals are interpreted as genetic distances. Obviously, the differences should reflect variations in DNA rather than artifacts due to a nonrobust method. Furthermore, the method should provide the appropriate level of discriminatory power, and it should be relatively rapid and cheap, especially in large-scale population genetic studies. Macrorestriction analysis of genomic DNA followed by pulsed-field gel electrophoresis (REA-PFGE) has become the "gold standard" for molecular typing (10). In recent years, some alternative techniques have been successfully applied for the typing of bacteria below the species level. These include amplification-based methods, such as amplified fragment length polymorphisms (11), random amplification of polymorphic DNA (3, 12, 13), and amplification of DNA fragments surrounding rare restriction sites (5, 6, 8). These techniques are now applied more and more because they involve less time, comparably low cos...

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Dr fimbriae of uropathogenic Eschericha coli strains are an example of surface-located adhesive structures assembled via the chaperone-usher pathway. These structures are crucial for specific attachment of bacteria to host receptors. Dr fimbriae are linear associates of DraE proteins, the structure of which is determined by a donor strand complementation between the consecutive subunits. The biogenesis of these structures is dependent on a function of the specific periplasmic chaperone and outer membrane usher proteins. In a consequence of these structural and assembly properties the potential unfolding of a single subunit in a linear associate would cause a destruction of fimbrial adhesion function. This correlates with the observed high resistance of fimbrial structures for denaturation. In this paper we show that the mechanism of thermal denaturation of DraE-sc protein is well described by an irreversible two-state model which is the reduced form of a Lumry-Eyring protein denaturation model. In theory of this model the observed stability of DraE-sc protein is determined by the high activation barrier for the unfolding stage N-->U. The microcalorimetry experiments permit to determine kinetic parameters of the DraE-sc unfolding process: energy of activation of 463.5 +/- 20.8 kJ.mol(-1) and rate constant of order 10(-17) s(-1). This corresponds to the dissociation/unfolding half-life of Dr fimbriae of 10(8) years at 25 degrees C. The FT-IR experiments show that the high stability of DraE is determined by the cooperative rigid protein core. The presented mechanism of kinetic stability of Dr fimbriae is probably universal to adhesive structures of the chaperone-usher type.

The precise diagnosis of an acute and recent Toxoplasma infection in pregnant women and the newborn child is important before treatment. This study describes a new Toxoplasma gondii IgG avidity test based on a combination of recombinant GRA1, GRA7 and SAG1 antigens and shows that this test is useful for diagnostic purposes and may replace the lysed, whole-cell antigens. Although more sera need to be tested, the results obtained here suggest that the IgG avidity test performed with rec-antigens correlated more with the stage of a T. gondii infection than the IgG avidity results obtained with the lysed, whole-cell antigen test, the VIDAS Toxo IgG avidity (bioMérieux).