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Biomedical subjects

J Havlícek

Publications and source records attributed to J Havlícek.

At least 19 recordsLinked to original sources
PubMed2001

Decrease of psychomotor performance in subjects with latent 'asymptomatic' toxoplasmosis.

Toxoplasma gondii is known to induce specific behavioural changes in its intermediate hosts. This is usually considered to be an evolutionary adaptation aimed to increase the probability of transmission of the parasite into its definitive host, the cat, by predation. In rodents an increase of reaction time as well as many other specific behavioural patterns have been observed. Here we report the results of our double blind study showing the significantly longer reaction times of 60 subjects with latent toxoplasmosis in comparison with those of 56 controls. Moreover, the existence of a positive correlation between length of infection and mean reaction time suggested that slow and cumulative effects of latent toxoplasmosis rather than a one-step (and possibly transient) effect of acute toxoplasmosis disease are responsible for the decrease of psychomotor performance of infected subjects. To our knowledge, this is the first study confirming the existence of such parasite-induced changes in human behaviour that could be considered in evolutionary history of the human species as adaptive from the point of view of parasite transmission.

Animals↗
PubMed2000

Synthesis and structure of 6-amino-2,3,6-trideoxy-D-erythro-hexono-1,6-lactam and 6-amino-3,6-dideoxy-D-xylo-hexono-1,6-lactam.

Solid-state conformations of 6-amino-2,3,6-trideoxy-D-erythro-hexono-1,6-lactam (3a) and 6-amino-3,6-dideoxy-D-xylo-hexono-1,6-lactam (7a) were determined using X-ray diffraction. Conformations of the compounds 3a, 7a, and their per-O-acetyl derivatives 4,5-di-O-acetyl-6-amino-2,3,6-trideoxy-D-erythro-hexono-1,6-lactam (3b) and 2,4,5-tri-O-acetyl-6-amino-3,6-dideoxy-D-xylo-hexono-1,6-lactam (7b) in solutions were deduced from the analysis of NMR spectra using a modified Karplus equation and compared with the results of circular dichroism measurement of lactams 3a and 7a. Conformation 4C(1,N) was revealed for solid lactams 3a and 7a and for lactams 7a and 7b in solution, while lactams 3a and 3b in solution exist in the approximately 1:1 equilibrium of the conformers 4C(1,N) and (1,N)C4.

Carbohydrate Conformation↗
PubMed1999

Changes in the personality profile of young women with latent toxoplasmosis.

Latent toxoplasmosis is the most widespread parasite infection in developed and developing countries. The prevalence of Toxoplasma gondii infection varies mostly between 20 to 80% in different territories. This form of toxoplasmosis is generally considered to be asymptomatic. Recently published results, however, suggest that the personality profiles of infected subjects differ from those of uninfected controls. These results, however, were obtained on non-standard populations (biologists or former acute toxoplasmosis patients). Here we studied the personality profiles of 191 young women tested for anti-Toxoplasma immunity during gravidity. The results showed that the differences between Toxoplasma-negative and Toxoplasma-positive subjects exits also in this sample of healthy women. The subjects with latent toxoplasmosis had higher intelligence, lower guilt proneness, and possibly also higher ergic tension. The difference in several other factors (desurgency/surgency, alaxia/protension, naiveté/shrewdness, and self-sentiment integration) concerned changes in the variances, rather than the mean values of the factors.

Adolescent↗
PubMed1993

[Popper's critical rationalism and the biomedical sciences].

Popper's rationalism makes an important contribution of the 20th century philosophy to the methodology of natural sciences. Through its criterion of falsification, it enabled the scientists to take a critical but constructive view on hypotheses, conjectures and theories. This attitude found its application also in medicine.

Logic↗
PubMed1987

Quantitative character of fibrinogen uptake by M+ and M- variants of Streptococcus pyogenes.

Fibrinogen was labelled with 125Iodine by mild chemical oxidation and its binding to Streptococcus pyogenes was subjected to quantitative analysis, inhibition and desorption studies. Fibrinogen was bound both by virulent and avirulent (M protein-positive and M protein-negative) matched strains of several serotypes. In all pairs of strains fibrinogen uptake was much higher by the M-positive variants. The ratio of bound fibrinogen to total fibrinogen was highly dependent both on the concentration of fibrinogen and the concentration of cocci. Equilibrium binding studies showed that the binding was a multifactorial process. Probably not only receptor fibrinogen interactions but also interactions between bound and unbound fibrinogen molecules took place. The uptake of fibrinogen was highly depressed in avirulent strains and practically uninfluenced in virulent strains by the presence of albumin or immunoglobulin. The bond between fibrinogen and streptococci is therefore different in virulent and avirulent variants. The fibrinogen receptors on the cell surface are specific.

Fibrinogen↗
PubMed1986

Type 1 M protein of Streptococcus pyogenes. N-terminal sequence and peptic fragments.

Limited proteolysis of the surface of type 1 Streptococcus pyogenes by pepsin gives rise to fragment Pep M1 of Mr 20270 as the main product which covers the N-terminal part of the M protein. The amino acid sequence was determined of the N-terminal region of the M protein representing the most exposed part of the molecule on the surface fibrils of streptococcal cells, which seems to be very important for the differentiation of the individual serological types. The sequence differs from the homologous N-terminal sequences of types 5, 6 and 24, and shows a homology with sequences repeating in the chain of type 24. Fragment Pep M1 binds to fibrinogen; the absence of its 30 N-terminal amino acid residues, however, abolishes this interaction which is believed to play a role in the virulence of S. pyogenes.

Amino Acid Sequence↗
PubMed1984

Comparative studies on surface hydrophobicity of streptococcal strains of groups A, B, C, D and G.

Cell surface hydrophobicity of group A, B, C, D and G streptococcal strains has been studied and compared in a new test based on the fact that the degree of bacterial aggregation in ammonium sulphate depends on amphiphilic surface antigens. M-positive group A strains showing good growth in normal human blood aggregated in the standard salt aggregation test at very low concentrations of ammonium sulphate, while M-negative strains, which were killed in normal human blood, usually aggregated at high salt concentrations. Agents such as 2 M-KSCN, 2 M-guanidine. HC1 or 2 M-urea decreased the aggregation of the M-positive strains in the salt aggregation test while non ionic detergents such as Tween 20 (1%, w/v) and ethylene glycol (2 M) did not affect cell aggregation. Binding of fibrinogen and albumin resulted in a decrease of surface hydrophobicity of the group A M-positive strains. Group B strains possess a hydrophilic surface character and did not aggregate, while group C and G strains behaved in the salt aggregation test like M-negative strains of group A streptococci. Group D strains did not aggregate even at high ammonium salt concentrations. The results are discussed in relation to the influence of lipoteichoic acid and other surface antigens on strains of the various groups, and it is suggested that M protein and possibly also other surface proteins contribute to the high surface hydrophobicity of group A strains.

Ammonium Sulfate↗
PubMed1984

Surface characteristics of group A streptococci with and without M-protein.

Twenty M protein-positive and eight M protein-negative strains of group A streptococci were investigated with respect to surface hydrophobicity and amount of lipoteichoic acid (LTA). Surface hydrophobicity as determined in polymer two-phase systems varied substantially between individual strains and there was no correlation to the presence of antiphagocytic M protein. The amount of LTA on the surface of the bacteria varied with hydrophobic affinity of the cells. Strains with a high content of surface LTA were found among both M-positive and M-negative streptococci. Cellular and extracellular LTA was estimated on six strains by the ability of hot phenol extracts and culture fluids to sensitize erythrocytes and by rocket immunoelectrophoretic quantitation. Differences in content of surface LTA did not correlate to differences in the total amount of cellular LTA. Pepsin digestion of M-positive group A streptococci at suboptimal pH resulted in a loss of M antigen whereas surface LTA and the hydrophobic interaction liability was retained. The results indicate that the degree of surface hydrophobicity as measured by two-phase partitioning is not correlated to either the type-specific or the antiphagocytic moiety of M protein. The results support the correlation between surface LTA and surface hydrophobicity of group A streptococci.

Antigens, Bacterial↗
PubMed1983

Demonstration of a receptor for mouse and human serum albumin in Streptococcus pyogenes.

A new type of surface receptor for serum albumin was detected in strains of Streptococcus pyogenes (group A). This receptor, called type e, was different from albumin receptors in other streptococcal species. Only mouse and human serum albumin was bound to the receptor. The albumin-binding capacity was high: 2 X 10(8) bacterial organisms bound 11 micrograms of mouse albumin. The receptor was stable even when treated at 100 degrees C for 5 min. Binding of albumin was not mediated by lipoteichoic acid (LTA) because of lack of correlation to surface LTA, restricted albumin reactivity, and positive binding in presence of 2% Tween 20. Presence of albumin receptor type e correlated to presence of M-protein as measured by growth in the bactericidal test. All 51 M-protein positive group A streptococcal strains tested could bind mouse albumin whereas only 3 out of 8 M-protein negative strains showed positive binding (P less than 0.001). The sensitivity to trypsin digestion suggests that the albumin receptor is of protein nature or mediated by a protein.

Animals↗
PubMed1980

Mitogenic and antigenic properties of group A streptococcal M protein preparations.

The separation of a mitogenic substance in M protein preparations of Streptococcus pyogenes, type 1 and type 12, is described. The isolation was achieved by gel chromatography on Biogel A 0.5 m, and by immunochromatography on immobilized type specific antibodies. In the delayed cutaneous hypersensitivity test the immunochromatography purified M 1 protein caused erythema but no unspecific mitogenicity could be found by lymphocyte transformation test. In neutralization experiments the mitogenic activity of M protein preparations was specifically inhibited by anti-erythrogenic toxin antisera.

Adult↗
PubMed1980

Adherence of group A streptococci to epithelial cells in tissue culture.

Using the HEp-2 cell line system the factors and mechanisms of group A Streptococcus adherence had been studied. It was shown that high adherence was chiefly found in strains showing attributes of virulence (presence of M protein, growth in human blood, lethality for mice). The data supplied by experiments with pepsin and LTA suggest that there exist at least two mechanisms of adherence.

Adhesiveness↗
PubMed1979

Isolation of type-specific antibody to streptococcus pyogenes by affinity chromatography.

Rabbit type-specific opsonic antibodies to type 1 and type 12 streptococci were isolated by affinity chromatography on immobilized phage-enzyme extract. They were tested by precipitation in gel, bactericidal test and radioimmunoassay. Only type-specific activities were demonstrated. These activities were distributed homogeneously according to avidity. No suggestion of opsonizing and precipitating activities being separable from each other was found. These highly purified rabbit antibodies were marked by radioiodination and used to titrate human anti-M antibodies by competition. These marked antibodies were also used for the study of type-specific antigenic determinants on streptococcal antigens.

Animals↗