Shear bond strength of resin luting cement to glass-infiltrated porous aluminum oxide cores

STATEMENT OF PROBLEM

Resin bonding surface treatment methods for conventional silica-based dental ceramics are not reliable for glass infiltrated high alumina content In-Ceram ceramics.

PURPOSE

This study developed an alternative surface treatment to improve resin bonding of glass-infiltrated aluminum oxide ceramic blasting with diamond particles and then observed the efficiency of this treatment. Material and methods. In-Ceram test specimens were prepared and divided into 2 groups. All specimens were sandblasted with Al(2)O(3), and blasted with diamond particles and 2 adhesive resins were applied. After bonding and storage in humid conditions, shear bond strength values were measured with a universal testing machine. Surface roughness and fracture interfaces were determined with a perthometer and a SEM.

RESULTS

The highest bond strength was obtained on the samples blasted with diamond particles (group II). The differences between the 2 groups and the 2 adhesive resin cements were both statistically significant.

CONCLUSION

Panavia-Ex cement exhibited higher bond strength than Super-Bond cement. This higher bond strength was attributed to ceramic oxide and ester bond and the mechanical properties of Panavia-Ex cement.

A ribozyme and a catalytic DNA with peroxidase activity: active sites versus cofactor-binding sites

BACKGROUND

An 18-nucleotide DNA oligomer, PS2.M, derived using an in vitro selection method was previously reported to bind hemin (Fe(III)-protoporphyrinIX) with submicromolar affinity. The DNA-hemin complex exhibited DNA-enhanced peroxidative activity. PS2. M is guanine-rich and requires potassium ions to fold to its active conformation, consistent with its forming a guanine-quaduplex. In investigating the specific catalytic features of PS2.M we tested the peroxidative properties of its RNA version (rPS2.M) as well as that of an unrelated DNA guanine-quadruplex, OXY4.

RESULTS

The hemin-binding affinity of rPS2.M was found to be 30-fold weaker than that of PS2.M. The UV-visible spectra and kinetics of enzymatic peroxidation of the RNA-hemin complex, however, were nearly identical to those of its DNA counterpart. Both displayed peroxidase activity substantially greater than those of heme proteins such as catalase and Fe(III)-myoglobin. Kinetic analysis suggested that PS2. M and rPS2.M catalyzed the breakdown of the hemin-hydrogen peroxide covalent complex to products. The hemin complex of folded OXY4 (which bound hemin as strongly as did rPS2.M) had a distinct absorption spectrum and only a minor peroxidase activity above the background level.

CONCLUSIONS

The results indicated that it is possible for RNA and DNA of the same sequence to fold to form comparable cofactor-binding sites, and to show comparable catalytic behavior. The results further suggest that only a subset of cofactor-binding sites formed within folded nucleic acids might be able to function as active sites, by providing the appropriate chemical environments for catalysis.

Left-isomerism sequence and maternal type-1 diabetes

Defects of lateralisation have previously been recognised in the offspring of women with type-1 diabetes. In a 3-year period, three of the six cases of left isomerism sequence notified to the Northern Region Congenital Abnormality Survey were the infants of diabetic mothers. This finding suggests a specific association between bilateral left-sidedness and maternal type-1 diabetes.

DNA enzymes

The past year has seen a coming-of-age in DNA enzyme research. Far from being laboratory curiosities, the activities of new DNA enzymes have broadened the known catalytic repertoire of nucleic acid enzymes, provided valuable insights into different mechanistic possibilities open to nucleic acid catalysts, and explored the importance for catalysis of native functionalities within DNA and RNA, as well as of a diversity of extrinsic cofactors. Thus, the first amino acid cofactor-utilizing DNA enzyme has been described, as well as DNA enzymes that cleave RNA without the assistance of any external cofactor. On the practical side, the most efficient RNA-cleaving nucleic acid enzyme described to date is a DNA enzyme.

DNA-enhanced peroxidase activity of a DNA-aptamer-hemin complex

BACKGROUND

In vitro selection (SELEX) previously identified short single-stranded DNAs that specifically bound N-methylmesoporphyrin IX (NMM), a stable transition-state analogue for porphyrin-metallation reactions. Interestingly, iron(III)-protoporphyrin (hemin) was a good competitive inhibitor for the DNA-catalyzed metallation reaction, and appeared to bind strongly to the NMM-binding DNA aptamers. We investigated the peroxidase activity of the aptamer-hemin complexes to see if the DNA component of the complex, like the apoenzymes in protein peroxidases, could enhance the low intrinsic peroxidatic activity of hemin.

RESULTS

Two porphyrin-binding DNA aptamers bound hemin with submicromolar affinity. The aptamer-hemin complexes had significantly higher peroxidase activity than hemin alone, under physiological conditions. The Vobs of the PS2.M-hemin complex was 250 times greater than that of hemin alone, and significantly superior to a previously reported hemin-catalytic-antibody complex. Preliminary spectroscopic evidence suggests the coordination of the hemin iron in the complex changes, such that the complex more closely resembles horseradish peroxidase and other heme proteins rather than hemin.

CONCLUSIONS

A new class of catalytic activity for nucleic acids is reported. The aptamer-hemin complexes described are novel DNA enzymes and their study will help elucidate the structural and functional requirements of peroxidase enzymes in general and the ways that a nucleic acid 'apoenzyme' might work to enhance the intrinsic peroxidatic ability of hemin. These aptamer-hemin complexes could be regarded as prototypes for redox-catalyzing ribozymes in a primordial 'RNA world'.

Hepatitis E virus infection in eastern India

Most cases of enterically transmitted non-A, non-B hepatitis in India have so far been attributed to hepatitis E virus (HEV) infection. Most of the documented studies of hepatitis have focused on the incidence of this disease in northern, western, and south central India. A small seroprevalence study was conducted in the eastern Indian city of Patna to assess the degree of HEV infection among acute sporadic hepatitis cases. Forty-two percent (24 of 57) of the cases of acute sporadic hepatitis were positive for anti-HEV antibodies. Absence of any serologic markers of hepatitis A, B, or E in 58% (33 of 57) of the cases with symptoms of acute hepatitis suggest that there may be as yet unidentified enterically transmitted viruses in this area.

Cation-regulated self-association of "synapsable" DNA duplexes

The simple innovation of introducing a block of G.G mismatches into a Watson-Crick DNA duplex permits two such duplexes, under conditions of physiological temperature and salt, to "synapse" with one another at their G.G mismatch sites via guanine-quartet formation. The short quadruplex formed at the "synapsed" site necessarily has its strands in an antiparallel, or partially antiparallel orientation. We wished to test whether a different, and more stable, synapsis might be achieved if one of the two strands in the synapsable duplex had its domain of guanine residues in a reverse orientation to the rest of the strand, via 5'-5' and 3'-3' linkages. Such modified duplexes might synapse via the formation of the thermodynamically preferred parallel quadruplex. Our results indicate that such "parallel" and "antiparallel" synaptic events have dramatically different requirements for cations. We use chemical probing experiments to provide evidence for a kinetic model for this discrepancy. It may be possible to exploit the distinct properties of the above two kinds of synapsable duplexes for a variety of in vivo and in vitro applications.

Occupational asthma in fruit salad processing

BACKGROUND

Three subjects employed in the preparation of fruit for fruit salads reported work-related respiratory symptoms. Their work entailed removing the peel from citrus fruits, primarily oranges, following soaking of the fruits in a bath of enzymes including fungal derived pectinase and glucanase. Objectives To investigate the respiratory symptoms reported by these workers and determine their causes.

METHODS

The three workers were investigated by a respiratory physician, including spirometry and serial peak flow measurements. Blood was taken for the measurement of IgE and IgG antibody responses against the enzyme solution.

RESULTS

Predominant symptoms in these workers were shortness of breath, chest tightness and wheezing which were all alleviated at weekends and holidays only to occur when returning to work. Serial peak flow measurements showed a clear work-related pattern. All three had strong IgE responses to the enzyme solution used at the workplace and showed distinct patterns of binding in immunoblots. All three improved immensely following withdrawal from the workplace environment.

CONCLUSION

Enzymes appear to be widely used in the preparation of fruit and although they are used in liquid form, exposure can occur to induce immunological sensitization and asthma.

Lanthanide probes for a phosphodiester-cleaving, lead-dependent, DNAzyme

Lanthanides are useful probes for studying metal ion interactions in biological systems. The trivalent cations of the lanthanide metals are unique in that their ionic radii and the first pKa values of bound water molecules vary monotonically along the period. In addition, the europium and terbium cations have the useful property that their luminescence is enhanced when bound to nucleic acids. We have found that lanthanide ions can function as effective co-factors for a lead-dependent, phosphodiester-cleaving catalytic DNA (DNAzyme). We used the unique properties of the lanthanide co-factors to study the metal binding site as well as the catalytic mechanism of the DNAzyme. The catalyzed lanthanide-mediated cleavage occurred at neutral pH and at room temperature, with multiple turnovers of substrate. A range of lanthanide ions could act as co-factors, but differentially, with the smaller lanthanides (Tb, Tm, Lu) being the most effective. The rate of cleavage of the phosphodiester did not vary linearly with either the ionic radius or the first pKa of lanthanide-coordinated water molecules. The DNAzyme appeared to use only a single bound lanthanide ion as co-factor. Luminescence spectroscopy with terbium revealed the importance of the 2' hydroxyl group at the cleavage site in lanthanide ion binding, and the substrate molecule alone appeared to generate substantially the catalytically relevant metal-binding site. This model system demonstrated further the utility of complexing lanthanide ions directly to DNA molecules for catalytic purposes. The use of lanthanide ions also provides a means for investigating the metal ion binding sites of nucleic acid enzymes in general.

The modus operandi of a DNA enzyme: enhancement of substrate basicity

BACKGROUND

We wished to investigate the mode of catalytic action of a small DNA enzyme (DNAzyme), PS5.M, that, when folded into an appropriate tertiary structure, catalyzes the insertion of copper and zinc ions into porphyrins such as mesoporphyrin IX (MPIX). PS5.M, originally derived from SELEX experiments for specific DNA binders of the distorted porphyrin N-methylmesoporphyrin (NMM), had enzymatic parameters (kcat/K(m) = 39,700 M-1 min-1; kcat/kuncat = 3,700) that rivalled those of an antibody that catalyzed the same reaction.

RESULTS

We used ultraviolet-visible absorption and fluorescence spectroscopy to study the mode of action of PS5.M and related catalytic DNA molecules. We found that the MPIX-DNAzyme complexes had absorption spectra more closely resembling those of the DNAzymes complexed to NMM than to the spectra of MPIX itself, whether MPIX was in its monomeric or aggregated form. pH titration experiments revealed that the DNAzyme raised the protonation pK for MPIX by 3-4 pH units.

CONCLUSIONS

Our results reveal that PS5.M works by enhancing the basicity (and hence the ease of metallation) of the bound porphyrin substrate. Large changes in the porphyrin's basicity may be brought about through distortion of the planar porphinato- core of MPIX to resemble that of the naturally deformed porphyrin NMM or through stabilization by a DNA phosphate of the growing positive charge in the transition state for porphyrin protonation/metallation or through a combination of the two. The catalytic strategy of enhancing substrate basicity may also hold true for porphyrin metallation by the recently described catalytic RNA and catalytic antibody for this reaction.

Surgical treatment of rectal prolapse. A retrospective analysis of 94 cases

METHODS

A retrospective analysis evaluating 94 patients who underwent posterior rectopexy in 48 patients (51%), resection with or without rectopexy in 19 patients (20%) and Delorme's procedure in 27 patients (29%) was carried out for rectal prolapse in the last 15 years. The surgical procedures are described in detail. Postoperative evaluation was possible in all patients and mean observation time was 3.2 years.

RESULTS

Mortality rate was zero. Recurrence was seen in 4 cases (4.2%), only after Delorme's procedures. The proportion of continent patients increased from 69.2% preoperatively to 91.6% postoperatively. Defecation difficulties and incomplete evacuation did not change beneficially after the surgery. Important postoperative complications, retrograde ejaculation and impotence were seen in 5 male patients (17.2) after posterior rectopexy, and were a major cause of dissatisfaction.

CONCLUSIONS

In conclusion, Delorme's procedure, posterior rectopexy and resection procedures are effective surgical operations for treatment of rectal prolapse but extensive pelvic dissection during the posterior rectopexy may create serious sexual problems in male patients.

Prospective population based survey of outcome of pregnancy in diabetic women: results of the Northern Diabetic Pregnancy Audit, 1994

OBJECTIVE

To determine whether the St Vincent declaration (1989) target of diabetic pregnancy outcome approximating non-diabetic pregnancy outcome in near to being achieved.

DESIGN

Prospective collection of population based information on pregnancies in women with diabetes from all participating hospitals.

SETTING

District general and teaching hospitals of the former Northern region.

SUBJECTS

111 diabetic women booking with pregnancy during 1 January to 31 December 1994.

MAIN OUTCOME MEASURES

Diabetic control, perinatal mortality rate, fetal abnormality rate.

RESULTS

The perinatal mortality rate was 48/1000 for diabetic pregnancies compared with 8.9/1000 for the background population (odds ratio 5.38; 95% confidence interval 2.27 to 12.70) and the neonatal mortality rate was 59/1000 compared with 3.9/1000 (15.0; 6.77 to 33.10). Two late neonatal deaths were due to congenital heart defects. Six per cent of all fetal losses (6/109 cases) were due to major malformations. The congenital malformation rate was 83/1000 compared with 21.3/1000 (3.76; 2.00 to 7.06) in the background population.

CONCLUSIONS

Diabetic pregnancy remains a high risk state with perinatal mortality and fetal malformation rates much higher than in the background population.

Evidence for the metal-cofactor independence of an RNA phosphodiester-cleaving DNA enzyme

BACKGROUND

RNA and DNA are polymers that lack the diversity of chemical functionalities that make proteins so suited to biological catalysis. All naturally occurring ribozymes (RNA catalysts) that catalyze the formation, transfer and hydrolysis of phosphodiesters require metal-ion cofactors for their catalytic activity. We wished to investigate whether, and to what extent, DNA molecules could catalyze the cleavage (by either hydrolysis or transesterification) of a ribonucleotide phosphodiester in the absence of divalent or higher-valent metal ions or, indeed, any other cofactors.

RESULTS

We performed in vitro selection and amplification experiments on a library of random-sequence DNA that incorporated a single ribonucleotide, a suitable site for cleavage. Following 12 cycles of selection and amplification, a 'first generation' of DNA enzymes (DNAzymes) cleaved their internal ribonucleotide phosphodiesters at rates approximately 10(7)-fold faster than the spontaneous rate of cleavage of the dinucleotide ApA in the absence of divalent cations. Re-selection from a partially randomized DNA pool yielded 'second generation' DNAzymes that self-cleaved at rates of approximately 0.01 min-1 (a 10(8)-fold rate enhancement over the cleavage rate of ApA). The properties of these selected catalysts were different in key respects from those of metal-utilizing ribozymes and DNAzymes. The catalyzed cleavage took place in the presence of different chelators and ribonuclease inhibitors. Trace-metal analysis of the reaction buffer (containing very high purity reagents) by inductively coupled plasma-optical emission spectrophotometry indicated that divalent or higher-valent metal ions do not mediate catalysis by the DNAzymes.

CONCLUSIONS

Our results indicate that, although ribozymes are sometimes regarded generically to be metalloenzymes, the nucleic acid components of ribozymes may play a substantial role in the overall catalysis. Given that metal cofactors increase the rate of catalysis by ribozymes only approximately 10(2)-10(3)-fold above that of the DNAzyme described in this paper, it is conceivable that substrate positioning, transition-state stabilization or general acid/base catalysis by the nucleic acid components of ribozymes and DNAzymes may contribute significantly to their overall catalytic performance.

Studies on some trace and minor elements in blood. A survey of the Kalpakkam (India) population. Part II: Reference values for plasma and red cell, and correlation with coronary risk index

Since data on the trace element levels in Indian population are lacking, we chose to conduct a survey of the Kalpakkam township population. People in the age group 40-55 were included in this study. Reference values for trace and minor elements of the blood of the Kalpakkam population were arrived at by carrying out the analysis of plasma and red cells of healthy subjects of the Kalpakkam population. Although the "reference values" for many elements were found to be normal and comparable to values available in the literature, slight deficiency with respect to Se was noticed. Subjects with high coronary risk index were also included in the study to assess the possible correlation of elemental and lipid profile. A study of box plots showed that the elements Se, Mg, Na, K, and Fe show significant differences between "high risk" coronary risk index (CRI > 5) and "no risk" (CRI < 4.5). In the plasma, the levels of Mg, Na, and K were found to be less in the high-risk group. In red cells, the amount of Se, Fe, and K were found to be significantly less in the "high-risk" group as compared to the "no-risk" group.

Toward an efficient DNAzyme

A 33-nucleotide, guanine-rich DNA oligomer, PS5.ST1, has been reported to catalyze the metallation of mesoporphyrin IX (MPIX) by copper and zinc ions. In this paper we report a thorough investigation of the properties of this DNAzyme. We have established that a 24-nucleotide sequence (PS5.M), from within PS5.ST1, is both the minimal and most optimal catalytic unit. We have found that three related porphyrins are acceptable as substrates by this DNAzyme, of which protoporphyrin IX is preferred as a substrate over the expected substrate, MPIX. We have determined that it is unlikely that a strong, catalytically relevant binding site for copper ions exists in the DNAzyme and that high concentrations of copper destroy the active DNAzyme. This enzyme, whose folded structure likely contains guanine quartets, requires potassium ions for activity; we have shown that as little as 1 mM potassium is sufficient for its catalytic robustness, whereas as much as 0.5 M sodium still will not support catalysis. In determining the pH, temperature, and salt optima for the catalyzed reaction, we have found an unexpected stabilizing role for Tris buffer in both the catalyzed and background metallation reactions. As a consequence of various steps of optimization, we now have a vastly improved DNAzyme, one whose enzymatic parameters compare well both with those of natural ferrochelatases, as well as with those of artificially derived chelatases, composed of protein (a catalytic antibody) and RNA. The existence of this array of biocatalysts for porphyrin metallations allows one-to-one comparisons of the ways in which different biopolymers solve a given catalytic problem.

The DNA structures at the ends of eukaryotic chromosomes

The sequence organisation of the telomeric regions is extremely similar for all eukaryotes examined to date. Subtelomeric areas may contain large sequence arrays of middle repetitive, complex elements that sometimes have similarities to retrotransposons. In between and within these complex sequences are short, satellite-like repeats. These areas contain very few genes and are thought to be organised into a heterochromatin-like domain. The terminal regions almost invariably consist of short, direct repeats. These repeats usually contain clusters of 2-4 G residues and the strand that contains these clusters (the G strand) always forms the extreme 3'-end of the chromosome. Thus, most telomeric repeats are clearly related to each other which in turn suggests a common evolutionary origin. A number of different structures can be formed by single-stranded telomeric G strand repeats and, as has been suggested recently, by the G strand. Since the main mechanism for the maintenance of telomeric repeats predicts the occurrence of single-stranded extensions of the G strand, the propensity of G-rich DNA to fold into alternative DNA structures may have implications for telomere biology.

General practices and health and safety at work

There is a lack of knowledge and understanding of health and safety legislation in general practice surgeries. As a result, compliance with such laws is also seriously lacking. However, both knowledge and compliance can be significantly improved through information, guidance and contact with the Health and Safety Executive (HSE).

Recognition of anionic porphyrins by DNA aptamers

DNA sequences were isolated by in vitro selection for binding to N-methylmesoporphyrin IX (NMM), a molecule that behaves as a stable transition-state analogue for porphyrin chelatases. Clones approximately 280 and approximately 120 nucleotides long were obtained, which bound to NMM with sub-micromolar affinity but bound mesoporphyrin IX (MPIX), as well as various metalloderivatives of MPIX, with lower affinity. Footprinting experiments with dimethyl sulfate, DNase I, and bound hemin molecules activated by superoxide identified a series of short guanine-rich motifs to be the binding sites for the various porphyrins. One clone, PS2, examined in depth, gave a methylation footprint with bound NMM but not with bound MPIX nor with a number of metalloporphyrins. The binding domain PS2, synthesized as a short oligonucleotide, itself showed high-affinity binding to NMM. The binding sequences from different clones were loosely homologous, and the footprinting data were consistent with their folding to form one or more guanine quartets in the presence of NMM. Ultraviolet--visible absorption and circular dichroism spectroscopy of the DNA--NMM complexes indicates, however, that the interaction is not primarily intercalative in nature. The preferential binding of NMM by these aptamers raises the possibility of their being able to catalyze the chelation of metal ions by the porphyrin MPIX.

Synapsable DNA

We describe a simple innovation that allows DNA double helices to stably bind one another at specific sites, with regulatable affinity, under physiological conditions. This type of DNA synapsis requires neither an unraveling of the participating duplexes not heteroduplex formation, and is achieved by the intermolecular dimerization of short blocks of guanine-guanine mismatch base-pairs introduced within standard Watson-Crick duplexes. We propose that in vivo such "sticky" guanine domains, formed transiently in cruciforms, could initiate illegitimate recombination events. In practical terms, this type of synapsis, achievable in vitro by simply mixing the participating duplexes, could provide a novel and general technology for the self-assembly of arrays of important DNA sequences, and serve as a tool for investigating certain protein-DNA interactions in vivo.

Enterotoxigenic Escherichia coli associated diarrhoea among infants aged less than six months in Calcutta, India

The role of enterotoxigenic Escherichia coli (ETEC) as etiologic agents of diarrhoea in infants aged less than six months was assessed in a hospital based study in Calcutta, India. Of the 218 cases examined, ETEC strains were isolated from 26 (11.9%) cases. Among these, in 17 cases ETEC was the sole infecting pathogen (p = 0.0085). Of the 26 isolates (each isolate representing a case), 24 were distributed among seven different O:K:H serotypes and two different colonization factor antigens (CFAs) I and II. Two of the remaining isolation were untypable, non-haemagglutinating, and were non-hydrophobic as measured by the salt aggregation test (SAT). Of the 26 ETEC strains detected, 15 (57.7%) produced heat-labile toxin (LT) only, 8 (30.8%) liberated heat-stable toxin (ST) only, and the remaining 3 (11.5%) produced both LT and ST. No ETEC strain was isolated from the 102 age-matched controls included in this study. All the ETEC isolates were multiple drug resistant. The study showed that the diarrhoea due to ETEC was of brief duration, mostly within the range of 3 to 7 days.

Manic depressive disorder and lithium over the decades: the very educational case of Mrs. L

BACKGROUND

Manic depressive disorder is a recurrent illness with a variable clinical course. Before the advent of modern pharmacotherapy, ECT was a common treatment; more recently, lithium has become the long-term treatment of choice, but it is a treatment that is not without complications.

METHOD

The psychiatric and medical history of an 80-year-old patient was reviewed and analyzed based on clinical interview and medical records. The findings were integrated with literature review to illustrate a number of important clinical points about manic depressive disorder and its treatment.

RESULTS

(1) ECT is an effective treatment for mania, (2) a sustained remission may occur spontaneously, (3) a mania-depression-euthymia episode sequence predicts favorable response to lithium, (4) lithium discontinuation is not without risk, (5) lithium continuation is not without risk (thyroid, kidneys, eyes).

CONCLUSION

The case of Mrs. L illustrates the longitudinal course of manic depressive disorder and how it can be influenced by treatment and withdrawal of treatment. It also illustrates the potential of lithium for causing adverse effects on several organ systems.

The significance of enteroaggregative Escherichia coli in the etiology of hospitalized diarrhoea in Calcutta, India and the demonstration of a new honey-combed pattern of aggregative adherence

Previous studies have identified enteroadherent Escherichia coli that exhibit localized adherence, diffuse adherence and atypical diffuse adherence as diarrhoeagenic agents associated with infantile diarrhoea in Calcutta, India. In this study, a DNA probe specific for enteroaggregative adherence was used to determine the etiological significance of enteroaggregative E. coli in the causation of diarrhoea. From a total of 330 strains of E. coli recovered from 159 cases of acute secretory diarrhoea and 174 cases of invasive diarrhoea, 20 strains hybridized with the probe, whereas of the 25 E. coli strains recovered from 25 healthy controls only 1 strain hybridized with the probe. Of the 21 probe positive strains, 19 adhered to HeLa cells in the typical stacked-brick pattern while 2 strains recovered from 2 cases of secretory diarrhoea adhered to the glass surface in a hitherto undescribed formation which we have termed, based on the appearance, as the honey-comb pattern. The enteroaggregative E. coli strains identified in this study did not produce any conventional enterotoxins and were significantly associated with patients with secretory diarrhoea (10.7%) than with invasive diarrhoea (1.7%). The results of this study indicate that enteroaggregative E. coli play a causal role in acute secretory diarrhoea in this part of the world which lends credence to the involvement of a potent toxin in the pathogenesis of EAggEC mediated infections.

Mode of dimerization of HIV-1 genomic RNA

Retroviral genomes consist of two identical RNA molecules joined noncovalently near their 5' ends, at domains called dimerization linked sequences (DLS). This physical linkage of the genomic RNAs is considered important for the control of several steps in the viral life cycle, such as recombination, translation, and encapsidation. The putative DLS of human immunodeficiency virus-1 (HIV-1), a 111-nucleotide, purine-rich stretch of RNA, has been found necessary and sufficient for a salt-induced dimerization of the genome in vitro. Our investigation into the mechanism of this dimerization reveals sharply varying influences of the different alkali cations on both the formation and the stabilization of the dimer, a pattern closely related to that of telomeric G-DNA complexes. To probe this phenomenon, we have carried out experiments using short antisense DNA oligomers to define the segments of the DLS that are required for dimerization and methylation protection to implicate sets of guanines in forming Hoogsteen hydrogen bonds within the dimer. Cumulatively, these data provide further evidence for the existence of guanine quartets within the dimerized HIV-1 DLS. We propose models in which guanine quartets not only allow the homodimerization of HIV-1 and other retroviral genomic RNAs but also permit the two RNA strands in a dimer to exist in an overall parallel orientation, as has been observed by electron microscopy.

Evaluation of conventional media for detection of colonization factor antigens of enterotoxigenic Escherichia coli

Strains of enterotoxigenic Escherichia coli producing either colonization factor antigen (CFA) I or II were tested for expression of CFA when grown on 16 different agar media by using agglutination and coagglutination with monoclonal antibodies, mannose-resistant hemagglutination, and a salt aggregation assay. CFA was detected from the CFA-positive strains when CFA agar was used, and it was also detected when other commercially available media were used, notably nutrient agar. CFA was not detected when other commercial media such as MacConkey agar were used. The use of nutrient agar with monoclonal antibody-based coagglutination reagents offers a potentially simple and rapid method for detecting E. coli which express CFA I or II.

Parallel and antiparallel G-DNA structures from a complex telomeric sequence

We investigated the formation in vitro of higher order structures by a DNA oligomer containing the terminal motif TGTG3TGTGTGTG3, derived from the Saccharomyces telomeric consensus, in order to (a) understand why certain cations favor the formation of parallel-stranded (G4 and G8) G-DNA structures, while others favor foldback, antiparallel structures (G'2) and (b) probe the structures of G-DNAs formed by this telomeric sequence, which is more complex than its well-studied counterparts from the protozoans oxytricha and tetrahymena. We find that dramatic switches in the formation of G4 versus G'2 structures occur in solutions of not only the group Ia cations, Li(+)-Cs+, but also in those of the group IIa cations, Mg(2+)-Ba2+. These data and the temperature-dependent formation and destruction of the different structures lend support to the kinetic scheme of Sen and Gilbert (1990), by which rapidly forming G'2 structures accumulate in highly stabilizing potassium (and strontium) solutions at the expense of the thermodynamically more stable G4 structures. Both the G4 and the G'2 complexes formed by the Saccharomyces sequence show novel structural features. Protection and interference experiments with dimethyl sulfate and potassium permanganate reveal that the core of alternating thymines and guanines within the telomeric motif plays a critical role in the stabilization of the parallel G4 structure, but not of the antiparallel G'2. Very likely, in the G4 complex, this GT core forms a novel higher order arrangement of alternating G and T quartets, the latter possibly comparable to the U quartets described by Cheong and Moore (1992) in their NMR study of the higher order structure formed by rUG4U.

Prospective study of nosocomial enteric infections in a pediatric hospital, Calcutta

Hospital acquired enteric infections were investigated by studying 3138 children under 5 years of age who were admitted without diarrhea in nine medical words of a pediatric hospital, Calcutta during the period between March and September 1987. Three hundred and twenty (10.2%) children developed nosocomial diarrhea during their hospital stay. Fecal samples from 178 nosocomial diarrhea, 345 hospitalized diarrhea cases, 178 hospital controls and 200 outpatient controls were collected for detection of established enteropathogens. There were no statistically significant differences in the detection of most of the enteropathogens from fecal samples of nosocomial diarrhea, hospitalized diarrhea and hospital controls. Enteric pathogens were detected at a higher frequency (statistically significant) from fecal samples of nosocomial diarrhea cases as compared to outpatient controls. This study highlights the importance of most of the enteropathogens like Shigella, Salmonella, rotavirus, enteropathogenic E. coli as the cause of hospital cross infection. This study reinforces the importance of developing preventive measures in order to reduce the frequency of illness.

Efficacy of norfloxacin for shigellosis: a double-blind randomised clinical trial

In a double-blind, randomised, clinical trial on 122 adults with acute Shigella dysentery, 60 patients were treated with norfloxacin and 62 with nalidixic acid. Of these, 32 patients in the norfloxacin group and 28 patients in the nalidixic acid group had Shigella in their stool. Patients of the two treatment groups were clinically comparable on admission. No significant differences in clinical responses were observed in the two groups among the Shigella-positive cases, Shigella-negative cases and among the total cases. All isolates of Shigella were susceptible to norfloxacin, whereas 13.8% of the strains were resistant to nalidixic acid.

Shigellosis in children: a prospective hospital based study

From 1985 to 1988, fecal samples of 950 hospitalized children suffering from diarrhea or dysentery were screened for Shigella species using standard methods. Shigella species were isolated as sole pathogen from 192 (20.2%) cases and S. flexneri type 2 was the predominant serotype. Shigella infection was prevalent throughout the year with high isolation rate during the summer and early monsoon months. Shigella strains isolated during the period were resistant to most of the commonly used drugs for the treatment of shigellosis. Nearly 16% of the Shigella strains were also resistant to nalidixic acid. Presence of blood and mucus in stools (dysentery) was the common clinical presentation of shigellosis cases. Malnutrition was associated with longer duration of illness. High cases fatality rate (16.7%) was observed among hospitalized children infected with Shigella.

Evaluation of the bead enzyme-linked immunosorbent assay for detection of cholera toxin directly from stool specimens

A highly sensitive bead enzyme-linked immunosorbent assay (bead ELISA) for detection of cholera toxin (CT) was evaluated for direct detection of CT from stool specimens of patients with acute secretory diarrhea. Of the 75 stool samples examined, 59 yielded biochemically, and serologically confirmed strains of Vibrio cholerae O1. The bead ELISA was positive for CT in stool supernatants in 50 (84.7%) of the 59 samples from which V. cholerae O1 was isolated. In addition, the bead ELISA was positive for three stool specimens which were negative by culture. The free CT present in 48 of the 50 stool samples positive by culture for V. cholerae O1 and for CT by bead ELISA was completely absorbed by anti-CT immunoglobulin G. All of the 59 strains of V. cholerae O1 biotype eltor isolated in this study produced in vitro CT. The concentration of CT present in the bead ELISA-positive stool samples ranged between 26 pg/ml and greater than 100 ng/ml. This evaluation study demonstrates that the bead ELISA is a sensitive and simple method for direct detection of CT in nonsterile stool samples, and we recommend routine use of this assay for detection of CT in stool samples and culture supernatants in clinical and reference laboratories.

Entero-adherent Escherichia coli is an important diarrhoeagenic agent in infants aged below 6 months in Calcutta, India

Escherichia coli adherent to HEp-2 and HeLa cells were isolated from the faeces of 43 (19.7%) of 218 hospitalised infants aged below 6 months with acute diarrhoea. No conventional virulence factors, including enterotoxin production--heat-labile (LT) or heat-stable (ST), the verotoxin (VT) or shiga-like toxin (SLT)--or the invasive phenotype (determined by the Sereny test) could be detected among these isolates. Out of the 43 isolates, 16 (37.2%) were of the known enteropathogenic O:K serogroups--enteropathogenic E. coli (EPEC). The remaining 27 (62.8%) isolates showed different types of adherence to HEp-2 and HeLa cells which was diffuse (40.7%), localised (37.0%), or both (22.3%); they were identified as entero-adherent E. coli (EAEC). The EAEC isolates adhered to HEp-2 and HeLa cells in the presence of mannose, lactose, fucose, galactose, and fetuin, indicating that adhesion was not specific for these sugars or glycoprotein. Haemagglutination and the salt aggregation test (SAT) did not correlate with patterns of adherence. The results of this study indicate that LA-EAEC is an important aetiological agent of acute diarrhoea in infants aged below 6 months in Calcutta.

Novel DNA superstructures formed by telomere-like oligomers

DNA oligomers containing three or more contiguous guanines form tetrastranded parallel complexes, G4-DNA, in the presence of alkali cations. However, oligomers that have a single multi-guanine motif at their 3' or 5' end, with a guanine as the terminal base, also form higher order products. Thus, the oligomer T8G3T forms a unique G4-DNA product at neutral pH in the presence of Na+, K+, or Rb+; however, its isomeric counterpart T9G3 in K+ or Rb+ generates an additional ladder of products of substantially lower gel mobility. We show that these larger complexes contain, respectively, 8, 12, or 16 distinct strands of oligomer. The octamer structure formed by T9G3 assembles in moderate salt at room temperature and melts around 60 degrees C in 100 mM KCl. Methylation protection experiments suggest a nested head-to-tail superstructure containing two tetraplexes bonded front-to-back via G quartets formed by out-of-register guanines. Naturally occurring chromosomal telomeres, which all have guanines at their 3' termini, may be able to form these superstructures.