Epidemiology of invasive pneumococcal disease in the Western Region, The Gambia

BACKGROUND

Streptococcus pneumoniae is a major cause of morbidity and mortality in young children in the developing world. The recent development of pneumococcal polysaccharide/protein conjugate vaccines may make possible prevention of this infection. However, little is known about the epidemiology of invasive pneumococcal disease in children in the developing world.

OBJECTIVES

To determine the incidence and epidemiologic features of invasive pneumococcal disease in children resident in a semiurban area of The Gambia.

METHOD

The study was part of a large trial of an Haemophilus influenzae type b vaccine that recruited 42 848 children at the age of 2 months during the period March, 1993, to October, 1995. Follow-up of study children continued until December 31, 1995; therefore the first children to enter the trial were followed for 2.5 years and the last for just a few months. During the period of surveillance, 2256 children were investigated for possible invasive pneumococcal disease when they presented to a hospital or health center.

RESULTS

We detected 110 cases of pneumococcal disease. Pneumonia was the most common form of invasive pneumococcal disease observed (75.5% of patients). The incidence of pneumococcal disease was 224 [95% confidence interval (CI) 171, 277] per 100,000 child years among children ages 2 to 11 months, 139 (95% CI 93, 184) per 100,000 among children ages 12 to 23 months and 82 (95% CI 21, 143) per 100,000 among children ages 24 to 35 months. Pneumococci of serogroups 14, 6, 5, 23, 19, 46 and 2 were isolated most frequently. Susceptibility to pneumococcal disease was not increased significantly among Haemophilus influenzae type b-vaccinated children.

CONCLUSIONS

The pneumococcus is a major cause of bacterial infection in The Gambia. A proposed nine-valent pneumococcal conjugate vaccine for developing countries containing conjugates of serogroups 1, 4, 5, 6, 9, 14, 18, 19 and 23 would cover 74% of cases of invasive pneumococcal disease in children resident in the Western Region of The Gambia.

Feature-extraction from endopeptidase cleavage sites in mitochondrial targeting peptides

Cleavage sites in nuclear-encoded mitochondrial protein targeting peptides (mTPs) from mammals, yeast, and plants have been analysed for characteristic physicochemical features using statistical methods, perceptrons, multilayer neural networks, and self-organizing feature maps. Three different sequence motifs were found, revealing loosely defined arginine motifs with Arg in positions -10, -3, and -2. A self-organizing feature map was able to cluster these three types of endopeptidase target sites but did not identify any species-specific characteristics in mTPs. Neural networks were used to define local sequence features around precursor cleavage sites.

Is urodilatin the missing link in exercise-dependent renal sodium retention?

The purpose of the present study was to investigate the behavior of plasma atrial natriuretic peptide [ANP-(99-126)] concentration ([ANP]) and renal urodilatin [Uro; ANP-(95-126)] excretion during and after exercise and their possible effects on renal Na+ retention. Ten male subjects performed a cycle ergometer test for 60 min at 60% of maximum workload. Blood and urine samples were collected before, during, and up to 24 h after exercise. During exercise, plasma [ANP] and renal Uro excretion were oppositely affected: whereas [ANP] increased from 46.5 +/- 5.1 to 124.1 +/- 10.6 pg/ml, urinary Uro excretion decreased from 120.8 +/- 16.0 to 49.5 +/- 9.8 fmol/min and remained at a lower level until 1 h after exercise. Glomerular filtration rate showed lowest values during exercise (from 164.9 +/- 15.3 to 75.8 +/- 10.1 ml/min), and urine flow and the fractional excretion rate of Na+ (FENa+) and Cl- (FECl-) had their nadir during the first hour after exercise. Positive relationships were observed between Uro excretion and FENa+ (P < 0.05) and FECl-, whereas a tendency toward a negative correlation was obtained between [ANP] and FENa+. It seems possible that Uro may be, among other factors, involved in the exercise-related regulation of renal Na+ retention. The specific roles Uro and ANP play during exercise, however, remain to be investigated.

Identification of catalytically important residues in yeast transketolase

The possible roles of four histidine residues in the active site of yeast transketolase were examined by site-directed mutagenesis. Replacement of the invariant His69 with alanine yielded a mutant enzyme with 1.5% of the specific activity of the wild-type enzyme and with an increased KM for the donor. This residue is located at the bottom of the substrate cleft close to the C1 hydroxyl group of the donor substrate, and the side chain of His69 might be required for recognition of this hydroxyl group and possibly for maintenance of the proper orientation of the reaction intermediate, (alpha, beta-dihydroxyethyl)thiamin diphosphate. Amino acid replacements of His481 by alanine, serine, and glutamine resulted in mutant enzymes with significantly increased KM values for the donor substrate and specific activities of 4.4%, 1.9%, and 5.5% of the wild-type enzyme. The kinetic data suggest that this residue, although close to the C2 carbonyl oxygen of the substrate, is not absolutely required for stabilization of the negative charge that develops at this oxygen in the transition state. This points toward the 4'-NH2 group of the pyrimidine ring of thiamin diphosphate as the major source of charge stabilization. Mutations at positions His30 and His263 result in mutant enzymes severely impaired in catalytic activity (1.5% and less of the activity of wild-type transketolase). The KM value for the donor substrate was increased for the His30Ala mutant but remained unchanged in the His263Ala enzyme. The side chains of both residues interact with the C3 hydroxyl group of the donor substrate, and the results indicate that the two residues act in concert during proton abstraction of the C3 hydroxyl proton during catalysis.

[Oral contrast media in CT: improvement by addition of guar?]

PURPOSE

To evaluate the additional effect of guar with iotrolan as an oral contrast medium.

METHOD

In a clinical double-blind randomised study a viscous iotrolan (11.2 mg iodine/ml)/guar (4 g/l)-suspension was compared with aqueous solutions of pure iotrolan (11.2 mg iodine/ml) and meglumine ioxithalamate (12 mg iodine/ml). The contrast media were evaluated according to filling, distribution, transit time, artifacts, radiodensity, patient acceptance and side effects.

RESULTS

The addition of guar delayed the transit time of the contrast media. Consequently a more homogeneous filling of the bowel with fewer artifacts was observed in comparison to the aqueous contrast media. The results of the pure iotrolan solution were comparable to meglumine ioxithalamate, except for a higher radiodensity in the distal small intestine. The colon showed a better filling with non-viscous contrast media in the given time frame. Pure iotrolan had the best patient acceptance. Two patients considered the iotrolan/guar-solution impossible to drink, the other 18 patients found taste and consistency just about acceptable.

CONCLUSION

In spite of the discussed advantages, due to a less subjective acceptance the guar/iotrolan solution is not suitable in routine-diagnosis, unless taste and consistency are greatly improved. Individual use is recommended in selected cases and long-term examinations.

Transmission X-ray microscopy of intact hydrated PtK2 cells during the cell cycle

Transmission X-ray microscopy makes it possible to investigate biological specimens, i.e. cells and organelles, in their natural wet environment. The main processes determining the contrast in X-ray microscopy are photoelectric absorption and phase shift. X-ray microscopic experiments can therefore be carried out in both amplitude and phase contrast. The Göttingen X-ray microscope at the BESSY storage ring in Berlin is described. PtK2 cells were examined during different stages of the cell cycle. All major constituents of the mitotic apparatus, e.g. chromosomes, centromeres, microtubules and centrosomes, could be visualized, as well as the main structural compartments and organelles of the interphase cell, e.g. nuclear membrane, interphase chromatin, nucleolus and cytoplasmic mitochondria, as well as parts of the cytoskeletal apparatus. In this way new information can be obtained with regard to the ultrastructure of the constituents of intact and unstained cells at a resolution which bridges the gap between light microscopy and electron microscopy. The prospects for the future application of transmission X-ray microscopy in biomedical research are discussed.

[Diffusion-weighted magnetic resonance imaging in the diagnosis of cerebral infarct]

Forty-one patients demonstrating clinical symptoms for cerebral infarction were investigated by magnetic resonance imaging with diffusion-weighted echo-planar imaging (DWI) and T2-weighted imaging (T2WI). In 8 patients only DWI showed the cerebral lesions clearly. One patient with positive DWI and T2WI suffered from HSV encephalitis. DWI is superior to T2WI in assessment of small cortical infarcts and cerebral infarction in patients with preexisting vascular lesions. DWI is not specific, so other causes like cerebral hematoma and encephalitis have to be considered.

The alternatively spliced domains EIIIB and EIIIA of human fibronectin affect cell adhesion and spreading

Fibronectin has a complex pattern of alternative splicing at the pre-mRNA level leading to the expression of different isoforms. The alternatively spliced domains EIIIB and EIIIA are known to be prominently expressed during development and wound healing. While the other spliced domain (CS-segment) is known to promote cell adhesion in a cell type specific manner, the biological functions of the spliced domains EIIIB and EIIIA are not well understood. In the present study, we have prepared expression proteins of specific domains of human fibronectin using a prokaryotic expression system and used the purified fragments to test their ability to support adhesion and spreading of cultured cells. Fragments from type-III domains #7 to #12 were prepared in various combinations to include or exclude the spliced domains EIIIB and EIIIA. The results indicate that cultured NIL fibroblasts adhere to many of the fragments tested. However, the cell adhesion and spreading are enhanced, especially at lower concentrations, to fragments including the domain EIIIB. The inclusion of domain EIIIA led to a decrease in the adhesion of cells and those that adhered did not spread well. When tested in a centrifugal cell adhesion assay, fragments including domain EIIIB resisted the detaching forces and stayed adhered. Fragments that included domain EIIIA were unable to resist the detaching centrifugal forces to the same extent as the fragments that included domain EIIIB alone. These results suggest that the spliced domain EIIIB may be serving important biological functions in enhancing cell adhesion and spreading. This is likely to be mediated by conformational effects because domain EIIIB alone neither exhibited any adhesive activity nor competed in inhibiting adhesion to fragments #7-10.

Residual neurologic sequelae after childhood cerebral malaria

BACKGROUND

Cerebral malaria is an important cause of pediatric hospital admissions in the tropics. It commonly leads to neurologic sequelae, but the risk factors for this remain unclear and the long-term outcome unknown.

OBJECTIVE

The purpose of this study was to identify the common forms of neurologic sequelae that occur after cerebral malaria, their evolution over time, and the major clinical risk factors for residual disability.

STUDY DESIGN

Prospective study in 624 children admitted with cerebral malaria to two hospitals in The Gambia, West Africa.

RESULTS

We found that 23.3% of survivors had neurologic sequelae on discharge from the hospital. By 1 month the proportion had decreased to 8.6%, and at 6 months only 4.4% of survivors were found to have residual neurologic sequelae. The most common forms of neurologic sequelae were paresis and ataxia, often found in combination with other neurologic abnormalities. In a multiple logistic regression analysis, depth of coma on admission, multiple convulsions, and duration of unconsciousness were the only three independent risk factors. Hypoglycemia and lactate acidosis were not predictive of sequelae, although they are important risk factors for fatality.

CONCLUSION

This finding raises the possibility that fatal outcome and neurologic sequelae arise from separate pathologic processes.

The ursodeoxycholic acid-p-aminobenzoic acid deconjugation test, a new tool for the diagnosis of bacterial overgrowth syndrome

OBJECTIVE

To determine the possible complementary role of the ursodeoxycholic acid-p-aminobenzoic acid (UDCA-PABA) loading test in the diagnosis of intestinal bacterial overgrowth.

DESIGN

A prospective clinical study.

PATIENTS AND METHODS

The hydrogen breath and UDCA-PABA tests were performed simultaneously in 68 patients with suspected contaminated small bowel syndrome (CSBS), and in 10 healthy control subjects. The hydrogen breath test was performed by oral loading of 25 g of lactose and/or 10 g of lactulose. The UDCA-PABA test was carried out by oral loading of 250 mg of UDCA-PABA conjugate, followed by measurement of the amount of PABA excreted in the urine. The diagnosis of bacterial overgrowth was considered to be established when either the hydrogen breath test or the UDCA-PABA test produced abnormal results.

RESULTS

Thirty-five of the 68 patients proved to have CSBS. In 13 of these 35 patients, only the enhanced urinary PABA excretion (11.7 +/- 1.42 mg vs. 3.6 +/- 0.68 mg) indicated bacterial overgrowth, 15 of the 35 patients gave only a positive hydrogen breath test, and in the remaining seven cases the results of both tests were abnormal. In eight CSBS patients, the urinary excretion of PABA was decreased significantly following 10-day tinidazole treatment (5.5 +/- 1.29 mg vs. 13.1 +/- 2.07 mg).

CONCLUSION

The UDCA-PABA test is a valuable clinical method for the detection of bacterial overgrowth, especially in cases where hydrogen production alone fails to reveal CSBS. It is also a useful procedure for evaluating the efficacy of antibacterial treatment.

Predictors of a fatal outcome following childhood cerebral malaria

Despite prompt treatment with an effective anti-malarial drug, cerebral malaria still has a mortality of 20-30%. To identify factors that may contribute to this high fatality rate, we have studied the relationship between clinical and laboratory features and a fatal outcome in 624 Gambian children with strictly defined cerebral malaria. One hundred twenty-four children (21.5%) died. Three-quarters of the deaths occurred within 24 hr of admission. Multiple logistic regression analysis showed that a cold periphery (odds ratio [OR] = 2.7), a deep coma (OR = 2.0), and hypoglycemia (OR = 4.1) were the clinical signs and laboratory parameters that predicted death most strongly. More than 90% of the children who died had at least one of these conditions. Also, children with elevated urea levels on admission or those who experienced multiple episodes of hypoglycemia or multiple convulsions subsequently were more likely to die. A combination of clinical and laboratory abnormalities can identify a group of children with cerebral malaria who are most at risk of dying, who require intensive care and who are candidates for new forms of therapy.

Circular permutations of natural protein sequences: structural evidence

Over the past few years, evidence has accumulated that shows that circularly permuted proteins resulting from permutations in their coding genes can indeed occur naturally. In most instances, these circularly permuted amino acid sequences have been detected by sequence alignment of homologous proteins. Circular permutations may escape detection, however, when based on sequence comparisons alone, as recently illustrated by transaldolase, a member of the class I aldolase family.

[The ursodeoxycholic acid-p-aminobenzoic acid test in the diagnosis of small bowel bacterial overgrowth syndrome]

Contaminated small bowel syndrome is frequently associated with meteorism due to excessive gas formation, and diarrhoea as a result of bacterial fermentative processes, including splitting of carbohydrates or deconjugating and dehydroxylating bile salts. In addition to gas production, bacteria capable of metabolizing bile salts have been shown to release p-aminobenzoic acid (PABA) from and Ursodeoxycholic-acid-PABA substrate. Our aim was to determine the possible complementary role of the UDCA-PABA test in the diagnosis of bacterial overgrowth.

PATIENTS AND METHODS

The H2 breath and UDCA-PABA tests were performed simultaneously on 46 patients with suspected contaminated small bowel syndrome, and on 7 healthy subjects. The H2 breath test was performed by oral loading of 25 g lactose and/or 10 g lactulose. The UDCA-PABA test was carried out by determining urinary excretion of PABA after oral loading with 250 mg UDCA-PABA conjugate. The diagnosis of bacterial overgrowth was established, when either H2 breath, or UDCA-PABA test proved to be pathological.

RESULTS

Based upon the pathologic values of either the H2 breath test, or the UDCA-PABA test, 25 out of 46 patients proved to have contaminated small bowel syndrome. In 10 out of 25 patients only pathologic urinary PABA excretion (12.772 +/- 1.707 vs 4.1 +/- 0.58), indicated bacterial overgrowth, and in 9 out of the same group only positive H2 breath test (early rise of > 20 ppm of H2) indicated the same, while in 6 cases both tests proved to be pathological. In 7 CSBS patients the urinary excretion of PABA significantly decreased following a 10 day Tinidazole treatment (5.48 +/- 1.286 vs 13.068 +/- 2.068).

CONCLUSION

The UDCA-PABA test proved to be a valuable complementary method to detect bacterial overgrowth, when H2 production failed to reveal bacterial overgrowth.

Crystal structure of nitrile hydratase reveals a novel iron centre in a novel fold

BACKGROUND

Nitrile hydratases are unusual metalloenzymes that catalyze the hydration of nitriles to their corresponding amides. They are used as biocatalysts in acrylamide production, one of the few commercial scale bioprocesses, as well as in environmental remediation for the removal of nitriles from waste streams. Nitrile hydratases are composed of two subunits, alpha and beta, and they contain one iron atom per alphabeta unit. We have determined the crystal structure of photoactivated iron-containing nitrile hydratase from Rhodococcus sp. R312 to 2.65 A resolution as a first step in the elucidation of its catalytic mechanism.

RESULTS

The alpha subunit consists of a long N-terminal arm and a C-terminal domain that forms a novel fold. This fold can be described as a four layered structure, alpha-beta-beta-alpha, with unusual connectivities between the beta strands. The beta subunit also contains a long N-terminal extension, a helical domain, and a C-terminal domain that folds into a beta roll. The two subunits form a tight heterodimer that is the functional unit of the enzyme. The active site is located in a cavity at the subunit-subunit interface. The iron centre is formed by residues from the alpha subunit only-three cysteine thiolates and two mainchain amide nitrogen atoms are ligands.

CONCLUSIONS

Nitrile hydratases contain a novel iron centre with a structure not previously observed in proteins; it resembles a hybrid of the iron centres of heme and Fe-S proteins. The low-spin electronic configuration presumably results in part from two Fe-amide nitrogen bonds. The structure is consistent with the metal ion having a role as a Lewis acid in the catalytic reaction.

Redesign of soluble fatty acid desaturases from plants for altered substrate specificity and double bond position

Acyl-acyl carrier protein (ACP) desaturases introduce double bonds at specific positions in fatty acids of defined chain lengths and are one of the major determinants of the monounsaturated fatty acid composition of vegetable oils. Mutagenesis studies were conducted to determine the structural basis for the substrate and double bond positional specificities displayed by acyl-ACP desaturases. By replacement of specific amino acid residues in a Delta6-palmitoyl (16:0)-ACP desaturase with their equivalents from a Delta9-stearoyl (18:0)-ACP desaturase, mutant enzymes were identified that have altered fatty acid chain-length specificities or that can insert double bonds into either the Delta6 or Delta9 positions of 16:0- and 18:0-ACP. Most notably, by replacement of five amino acids (A181T/A200F/S205N/L206T/G207A), the Delta6-16:0-ACP desaturase was converted into an enzyme that functions principally as a Delta9-18:0-ACP desaturase. Many of the determinants of fatty acid chain-length specificity in these mutants are found in residues that line the substrate binding channel as revealed by x-ray crystallography of the Delta9-18:0-ACP desaturase. The crystallographic model of the active site is also consistent with the diverged activities associated with naturally occurring variant acyl-ACP desaturases. In addition, on the basis of the active-site model, a Delta9-18:0-ACP desaturase was converted into an enzyme with substrate preference for 16:0-ACP by replacement of two residues (L118F/P179I). These results demonstrate the ability to rationally modify acyl-ACP desaturase activities through site-directed mutagenesis and represent a first step toward the design of acyl-ACP desaturases for the production of novel monounsaturated fatty acids in transgenic oilseed crops.

Monitoring depth of anaesthesia

In clinical practice, indirect and non-specific signs are used for monitoring anaesthetic adequacy. These include haemodynamic, respiratory, muscular and autonomic signs. These measures do not indicate adequacy of anaesthesia in a reliable manner. Many attempts have been made to find a more accurate monitor. Direct monitoring of anaesthetic effect should be possible by EEG measurement. EEG information can be reduced, condensed and simplified, leading to single numbers (spectral edge frequency and median frequency). These methods appear insufficient for assessing anaesthetic adequacy. The bispectral index, derived from bispectral analysis of the EEG, is a very promising tool for measuring adequacy of anaesthesia. An alternative approach is to monitor evoked potentials. Middle latency auditory evoked potentials may be helpful in assessing anaesthetic adequacy. Both techniques need further validation.

Randomised trial of Haemophilus influenzae type-b tetanus protein conjugate vaccine [corrected] for prevention of pneumonia and meningitis in Gambian infants

BACKGROUND

In developing countries, pneumonia and meningitis due to Haemophilus influenzae type b (Hib) are common in children under age 12 months and the mortality from meningitis is high. Protein-polysaccharide conjugate vaccines have brought Hib disease under control in industrialised countries. We did a double-blind randomised trial in The Gambia to assess the efficacy of a Hib conjugate vaccine for the prevention of meningitis, pneumonia, and other invasive diseases due to Hib.

METHODS

Between March, 1993, and October, 1995, 42,848 infants were randomly allocated the conjugate vaccine Hib polysaccharide tetanus protein (PRP-T) mixed with diphtheria-tetanus-pertussis vaccine (DTP), or DTP alone at age 2 months, 3 months, and 4 months. Children who presented with signs of invasive Hib were investigated by blood culture and, where appropriate, by lumbar puncture, chest radiograph, or percutaneous lung aspirate. Children were followed up for between 5 and 36 months.

FINDINGS

The median ages at which children received the study vaccine were 11 weeks, 18 weeks, and 24 weeks. 83% of children enrolled received all three doses of vaccine. 17 cases of culture-positive Hib pneumonia, 28 of Hib meningitis, and five of other forms of invasive Hib disease were detected amongst the study children. The efficacy of the vaccine for the prevention of all invasive disease after three doses was 95% (PRP-T vaccinees 1, controls 19 [95% CI 67-100]), for the prevention of Hib pneumonia after two or three doses, 100% (vaccinees 0, controls 10 [55-100]), and for the prevention of radiologically defined pneumonia at any time after enrollment, 21.1% (PRP-T vaccinees 198, controls 251 [4.6-34.9]).

INTERPRETATION

PRP-T conjugate Hib vaccine prevented most cases of meningitis and pneumonia due to Hib in Gambian infants. The reduction in the overall incidence of radiologically defined pneumonia in PRP-T vaccinees suggests that about 20% of episodes of pneumonia in young Gambian children are due to Hib. The introduction of Hib vaccines into developing countries should substantially reduce childhood mortality due to pneumonia and meningitis.

Examination of the thiamin diphosphate binding site in yeast transketolase by site-directed mutagenesis

The role of two conserved amino acid residues in the thiamin diphosphate binding site of yeast transketolase has been analyzed by site-directed mutagenesis. Replacement of E162, which is part of a cluster of glutamic acid residues at the subunit interface, by alanine or glutamine results in mutant enzymes with most catalytic properties similar to wild-type enzyme. The two mutant enzymes show, however, significant increases in the K0.5 values for thiamin diphosphate in the absence of substrate and in the lag of the reaction progress curves. This suggests that the interaction of E162 with residue E418, and possibly E167, from the second subunit is important for formation and stabilization of the transketolase dimer. Replacement of the conserved residue D382, which is buried upon binding of thiamin diphosphate, by asparagine and alanine, results in mutant enzymes severely impaired in thiamin diphosphate binding and catalytic efficiency. The 25-80-fold increase in K0.5 for thiamin diphosphate suggests that D382 is involved in cofactor binding, probably by electrostatic compensation of the positive charge of the thiazolium ring and stabilization of a flexible loop at the active site. The decrease in catalytic activities in the D382 mutants indicates that this residue might also be important in subsequent steps in catalysis.