Genetic linkage of exotoxin alleles and emm gene markers for tissue tropism in group A streptococci

In group A streptococci, genetic markers for principal tissue reservoir are located within emm genes, which encode surface proteins that have a role in virulence. A worldwide collection of 160 isolates was evaluated for two traits: chromosomal emm gene markers for tissue tropism (designated patterns A-E), and bacteriophage-associated genes (speA and speC) encoding pyrogenic exotoxins. The speA and speC alleles of organisms harboring the emm marker for a pharyngeal reservoir (pattern A-C) differ from spe alleles that predominate in organisms with the emm marker for impetigo (pattern D). However, organisms that display the emm marker for both tissue sites (pattern E) are not intermediate for the distribution of either speA or speC alleles, but instead resemble pattern A-C isolates for speA and pattern D strains for speC. Statistically significant nonrandom associations between exotoxin alleles and emm patterns were observed but cannot be readily explained by niche separation alone.     

High-frequency intracellular infection and erythrogenic toxin A expression undergo phase variation in M1 group A streptococci

The complex pathophysiology of lung allergic inflammation and bronchial hyperresponsiveness (BHR) that characterize asthma is achieved by the regulated accumulation and activation of different leukocyte subsets in the lung. The development and maintenance of these processes correlate with the coordinated production of chemokines. Here, we have assessed the role that different chemokines play in lung allergic inflammation and BHR by blocking their activities in vivo. Our results show that blockage of each one of these chemokines reduces both lung leukocyte infiltration and BHR in a substantially different way. Thus, eotaxin neutralization reduces specifically BHR and lung eosinophilia transiently after each antigen exposure. Monocyte chemoattractant protein (MCP)-5 neutralization abolishes BHR not by affecting the accumulation of inflammatory leukocytes in the airways, but rather by altering the trafficking of the eosinophils and other leukocytes through the lung interstitium. Neutralization of RANTES (regulated upon activation, normal T cell expressed and secreted) receptor(s) with a receptor antagonist decreases significantly lymphocyte and eosinophil infiltration as well as mRNA expression of eotaxin and RANTES. In contrast, neutralization of one of the ligands for RANTES receptors, macrophage-inflammatory protein 1alpha, reduces only slightly lung eosinophilia and BHR. Finally, MCP-1 neutralization diminishes drastically BHR and inflammation, and this correlates with a pronounced decrease in monocyte- and lymphocyte-derived inflammatory mediators. These results suggest that different chemokines activate different cellular and molecular pathways that in a coordinated fashion contribute to the complex pathophysiology of asthma, and that their individual blockage results in intervention at different levels of these processes.     

Relation between neonatal pneumonia and maternal carriage of group B streptococci

Obstetrical and neonatal complications were studied among 143 urogenital carriers of group B streptococci (GBS) and their 144 infants and compared with complications occurring in a control group of 157 pregnant non-carriers and their 158 infants. All parturients had experienced uncomplicated pregnancies until week 36. 26 infants, 13 from each group, were transferred to the neonatal intensive care unit for treatment and observation within the first 7 days of life. Among these infants, 11/13 infants of GBS carriers contracted pneumonia and pulmonary adaptation syndrome, in contrast to 3/13 infants of non-carriers (p less than 0.05). The GBS carrier infants transferred to the neonatal intensive care unit had higher birth weights and higher gestational ages. Within the group of infants born to GBS carriers, those with pulmonary diseases evidenced abnormal fetal heart rate changes during labour in a higher rate than in the controls. Puerperal endometritis occurred with a significantly higher frequency among the GBS carriers (7/143) than among the non-carriers (0/157). Maternal carriage of GBS is a high risk factor for both the mother and her newborn, also after an otherwise uncomplicated pregnancy.     

The relationship between smoking and triglyceride-rich lipoproteins is modulated by genetic variation in the glycoprotein IIIa gene

In the last year, several studies have reported conflicting results concerning an association between the PI(A2) allele of the PI(A1/A2) polymorphism of platelet glycoprotein IIIa and the risk of myocardial infarction. In the present study, we analyzed the hypothesis of whether glycoprotein IIIa genotypes have any association with lipids and lipoproteins as classical cardiovascular risk factors. Smoking, associated with changes in triglyceride-rich lipoprotein (TRL) concentrations and with both hypercoagulability and reduced fibrinolysis, was also analyzed as an environmental factor. Blood samples were obtained from 170 subjects (83 men and 87 women; mean age, 57 years; SD 15) recruited by random sampling from the census of Girona, Spain. Subjects were classified as current smokers (n=41) and nonsmokers or exsmokers (n=129). Whereas no differences were found in lipid and lipoprotein concentrations between smokers and nonsmokers in subjects with the PI(A1/A1) genotype, smokers with the PI(A1/A2) or PI(A2/A2) genotypes showed significantly higher triglyceride and very-low-density lipoprotein (VLDL) triglyceride concentrations than nonsmokers or exsmokers with the same genotypes. Similarly, the VLDL triglyceride/HDL cholesterol ratio was significantly different in subjects with the PI(A1/A2) or PI(A2/A2) genotypes stratified according to smoking status. Further analysis revealed a significant interaction between smoking and genotype when those homozygous for the allele PI(A1) were compared with one or two PI(A2) alleles for the three lipidic parameters. The observed effects appear to show links between smoking, triglyceride metabolism, and a glycoprotein involved in platelet aggregation. It is likely that the pI(A) polymorphism is in linkage disequilibrium with other functional mutations that might influence triglyceride metabolism under some environmental factors such as smoking. This finding may provide a new perspective in the complex relationship between glycoprotein IIIa gene, environment, and their interactions.     

Nonlinear genetic relationships between traits and their implications on the estimation of genetic parameters

To estimate nonlinear genetic relationships between traits, formulas based on the paternal halfsib analysis theory were derived. To illustrate the usefulness of the formulas, a series of data sets with halfsib structure for some preselected parameters and sample size situations were generated by means of Monte Carlo techniques. When a nonlinear relationship in the form of a polynomial relationship of degree two is present, the linear and quadratic regression coefficients can be estimated from a paternal halfsib analysis without bias. Some of the traditional linear genetic parameters need correction; however, their value is limited if the relationship between two traits is nonlinear. Although regression coefficients may be estimated appropriately in many situations, the application of the described method is restricted to situations in which the causal flow between the traits involved is clear and the heritability of the determining trait is larger than approximately .10. Further work should be directed to investigation of possibilities for including such parameters in selection decisions in a formalized way.     

Genetic variation and population structure of the Japanese sika deer (Cervus nippon) in Hokkaido Island, based on mitochondrial D-loop sequences

The purpose of this 30-month study was to explore the effectiveness of a caries-preventive regimen in lowering the salivary mutans streptococci level in pregnant women and, subsequently, in inhibiting the growth of these bacteria in their young children. Beginning at the end of the sixth month of pregnancy and continuing until delivery, subjects rinsed daily with 0.05 percent sodium fluoride and 0.12 percent chlorhexidine. The authors monitored the salivary mutans streptococci levels during the last six months of pregnancy and every six months thereafter for 24 months. They also measured bacterial levels in the children every six months until they reached age 24 months. The results show that treatment significantly reduced salivary mutans streptococci levels in mothers and delayed the colonization of bacteria in their children for about four months.     

Population structure in Daphnia obtusa: quantitative genetic and allozymic variation

Quantitative genetic analyses for body size and for life history characters within and among populations of Daphnia obtusa reveal substantial genetic variance at both hierarchical levels for all traits measured. Simultaneous allozymic analysis on the same population samples indicate a moderate degree of differentiation: GST = 0.28. No associations between electrophoretic genotype and phenotypic characters were found, providing support for the null hypothesis that the allozymic variants are effectively neutral. Therefore, GST can be used as the null hypothesis that neutral phenotypic evolution within populations led to the observed differentiation for the quantitative traits, which I call QST. The results of this study provide evidence that natural selection has promoted diversification for body size among populations, and has impeded diversification for relative fitness. Analyses of population differentiation for clutch size, age at reproduction, and growth rate indicate that neutral phenotypic evolution cannot be excluded as the cause.     

Contrasting population structure from nuclear intron sequences and mtDNA of humpback whales

Powerful analyses of population structure require information from multiple genetic loci. To help develop a molecular toolbox for obtaining this information, we have designed universal oligonucleotide primers that span conserved intron-exon junctions in a wide variety of animal phyla. We test the utility of exon-primed, intron-crossing amplifications by analyzing the variability of actin intron sequences from humpback, blue, and bowhead whales and comparing the results with mitochondrial DNA (mtDNA) haplotype data. Humpback actin introns fall into two major clades that exist in different frequencies in different oceanic populations. It is surprising that Hawaii and California populations, which are very distinct in mtDNAs, are similar in actin intron alleles. This discrepancy between mtDNA and nuclear DNA results may be due either to differences in genetic drift in mitochondrial and nuclear genes or to preferential movement of males, which do not transmit mtDNA to offspring, between separate breeding grounds. Opposing mtDNA and nuclear DNA results can help clarify otherwise hidden patterns of structure in natural populations.     

Probing the genetic population structure of Trypanosoma cruzi with polymorphic microsatellites

We describe here the identification of eight polymorphic microsatellite loci with (CA)n repeats in the Trypanosoma cruzi genome based on the affinity capture of fragments using biotinylated (CA)12 attached to streptavidin-coated magnetic beads. The presence of two peaks in PCR amplification products from individual clones confirmed that T. cruzi is diploid. Hardy-Weinberg and linkage disequilibrium analyses suggested that sexual reproduction is rare or absent and that the population structure is clonal. Several strains, especially those isolated from nonhuman sources, showed more than two alleles in many loci demonstrating that they were multiclonal. The phylogenetic analysis of T. cruzi based on microsatellites revealed a great genetic distance among strains, although the strain dispersion profile in the Wagner network was in general agreement with the species dimorphism found by PCR amplification of the divergent region of the rRNA 24Salpha gene.     

Quantitative genetic variation of odor-guided behavior in a natural population of Drosophila melanogaster

Quantitative genetic variation in behavioral response to the odorant, benzaldehyde, was assessed among a sample of 43 X and 35 third chromosomes extracted from a natural population and substituted into a common inbred background. Significant genetic variation among chromosome lines was detected. Heritability estimates for olfactory response, however, were low, as is typical for traits under natural selection. Furthermore, the loci affecting naturally occurring variation in olfactory response to benzaldehyde were not the same in males and females, since the genetic correlation between the sexes was low and not significantly different from zero for the chromosome 3 lines. Competitive fitness, viability and fertility of the chromosome 3 lines were estimated using the balancer equilibrium technique. Genetic correlations between fitness and odor-guided behavior were not significantly different from zero, suggesting the number of loci causing variation in olfactory response is small relative to the number of loci causing variation in fitness. Since different genes affect variation in olfactory response in males and females, genetic variation for olfactory response could be maintained by genotype x sex environment interaction. This unusual genetic architecture implies that divergent evolutionary trajectories for olfactory behavior may occur in males and females.     

Selective attachment of beta-haemolytic streptococci group A to oropharyngeal epithelium in health and disease

Localization and semiquantification of beta-haemolytic streptococci, Group A (GABHS), GABHS attachment and general bacterial attachment to epithelial cells (bacterial number and morphology) were studied during GABHS-positive acute tonsillitis and pharyngitis infections and among healthy GABHS carriers. Samples were collected from various areas of the oropharynx (palatine tonsils, posterior oropharyngeal wall, palatoglossal arch and buccal mucosa). During acute tonsillitis and pharyngitis, GABHS grew in samples obtained from the palatine tonsils and posterior oropharyngeal wall. The ratio of GABHS colonies to other aerobic colonies increased, and GABHS became attached to epithelial cells of both palatine tonsils and posterior oropharyngeal wall. In GABHS carriers, GABHS were found mainly on the palatine tonsils, but these microorganisms were not attached to the epithelium. Overall bacterial attachment to tonsillar and oropharyngeal epithelial cells increased during active tonsillitis and pharyngitis.     

Mapping a conserved conformational epitope from the M protein of group A streptococci

The carboxyl terminus of the M protein of group A streptococci (GAS) is highly conserved and contains epitopes that have been shown to induce opsonic antibodies and protection against GAS infection. This region of the protein can also stimulate T cells, which can react in vitro with heart antigens. Since different segments of the carboxyl terminus may be involved in immunity to GAS and in the pathogenesis of autoimmune disease (rheumatic heart disease), it is important to precisely define critical epitopes. However, the M protein is known to be a coiled coil, and a critical immunodominant antibody-binding epitope within this region (peptide 145, a 20-mer with the sequence LRRDLDASREAKK-QVEKALE) is shown here to be conformational. Thus, small synthetic overlapping peptides of 8-12 amino acids in length that span peptide 145 (p145) were unable to capture antibodies present in p145-immune mouse sera or in endemic human sera, even though antibodies raised to these small peptides coupled to diphtheria toxoid could bind the smaller peptides and, in some cases, p145. A series of mutated peptides in which every residue of p145 was sequentially altered also failed to identify critical residues for antibody binding. We thus devised a strategy to produce chimeric peptides in which small peptides copying the M protein sequence were displayed within a larger 28-mer peptide derived from the sequence of the GCN4 leucine zipper DNA binding protein of yeast. A 12-amino-acid window of the p145 sequence was inserted into the GCN4 peptide in such a way as to preserve any potential helical structure. The window was moved along one residue at a time to give a series of peptides representing p145. Circular dichroism demonstrated that these larger chimeric peptides and p145, but not a shorter 12-mer peptide, displayed alpha-helical potential in 50% trifluoroethanol. Certain chimeric peptides efficiently captured antibodies specific for p145 and thus enabled us to map the minimal antibody-binding sequence. RRDLDASREAKK, referred to as J(1)2. The chimeric peptide containing this sequence, referred to as J2, was able to inhibit opsonization of GAS by human antisera containing anti-peptide 145 antibodies. The T-cell response from p145-immunized responder B10.BR mice to J2 and J(I)2 was much lower than the response to p145 and mapped to a different peptide.     

Vaccination and the population structure of antigenically diverse pathogens that exchange genetic material

Populations of antigenically diverse pathogens undergoing genetic exchange may be categorized into strains on the basis of a set of principal protective antigens. The extent to which polyvalent vaccines based on these protective antigens can alter the population structure of the pathogen is determined by the degree of cross-protection between strains. In the case where there is no cross-protection, vaccinating against a particular strain will have no effect on the others. As cross-protection increases, the strains containing the antigenic variants included in the vaccine will be diminished in prevalence, and those that do not will increase in prevalence. The rise in prevalence of the latter will become more and more exaggerated as cross-protection increases. However, beyond a critical level of cross-protection, in the absence of vaccination, the steady state of the system is asymmetric in that a certain subset of strains (with non-overlapping repertoires of antigenic variants) will dominate over the others in terms of prevalence. Under these circumstances, a vaccine consisting of the most immunogenic combinations of antigenic variants can cause a dramatic increase in frequency of a subset of rare strains.     

Certain features of carbohydrate metabolism in phosphomycin-resistant avirulent forms of group A streptococci

A model of acute spinal and phantom pain syndromes caused by the formation of an abnormally increased excitation generator (AIEG) in the system of dorsal horns of the spine was used to study the effects of sodium valproate when used chronically in the phantom pain syndrome, when given in a single dose in the acute pain syndrome and when applied to the spine with disinhibitors inducing the pain syndrome. It was shown that during chronic administration sodium valproate produced a stress-preventive action, but failed to affect pain sensation and to prevent the development of the pain syndrome. When used in the acute pain syndrome, sodium valproate had a marked analgesic effect, and when applied to the spine it substantially reduced the manifestations of the pain syndrome. The action of sodium valproate on the AIEG can be accounted for by the higher GABA level that results in the hyperpolarization of neurons which are a part of AIEG. When the latter is formed and operates in acute and chronic pain syndromes there are differences in the functional activity of the neurochemical structures responsible for the realization of pain reaction components. This is suggested by varying effects of sodium valproate on pain sensation during acute and chronic experiments.     

Analysis of genetic structure and dispersal patterns in a population of sea beet

A model of the migration pattern in a metapopulation of sea beet (Beta vulgaris L. ssp. maritima), based on the continuous distributions of seed and pollen movements, is fitted to gene frequency data at 12 isozyme and RFLP loci by maximum likelihood by using an approximation of the simultaneous equilibrium distribution of the gene frequencies generated by the underlying multivariate stochastic process of genetic drift in the population. Several alternative restrictions of the general model are fitted to the data, including the island model, a model of complete isolation, and a model in which the seed and pollen dispersal variances are equal. Several likelihood ratio tests between these alternatives are performed, and median bias in the estimated parameters is corrected by using parametric bootstrapping. To assess the fit of the selected model, the predicted covariances are compared with covariances computed from the data directly. The dependency of estimated parameters on the ratio between effective and absolute subpopulation sizes, which is treated as a known parameter in the analysis, is also examined. Finally, we note that the data also appear to contain some information about this ratio.     

SXT and Taxo A disks for presumptive identification of group A and B streptococci in throat cultures

A bacitracin (0.04 units, BBL)-SXT (trimethoprim, 1.25 mg, plus sulfamethoxazole, 23.75 mg, BBL) susceptibility test was 94% accurate in presumptively identifying streptococci as either group A, B or not group A and B.     

Global matrilineal population structure in sperm whales as indicated by mitochondrial DNA sequences

The genetic variability and population structure of worldwide populations of the sperm whale was investigated by sequence analysis of the first 5'L 330 base pairs in the mitochondrial DNA (mtDNA) control region. The study included a total of 231 individuals from three major oceanic regions, the North Atlantic, the North Pacific and the Southern Hemisphere. Fifteen segregating nucleotide sites defined 16 mtDNA haplotypes (lineages). The most common mtDNA types were present in more than one oceanic region, whereas ocean-specific types were rare. Analyses of heterogeneity of mtDNA type frequencies between oceans indicated moderate (GST = 0.03) but statistically significant (p = 0.0007) genetic differentiation on a global scale. In addition, strong genetic differentiation was found between potential social groups (GST = 0.03-0.6), indicating matrilineal relatedness within groups. The global nucleotide diversity was quite low (pi = 0.004) implying a recent common mtDNA ancestry (< 100,000) years ago) and a young global population structure. However, within this time period, female dispersal has apparently been limited enough to allow the development of global mtDNA differentiation. The results are consistent with those from observational studies and whaling data indicating stable social affiliations, some degree of area fidelity and latitudinal range limitations in groups of females and juveniles.