Variation in the Promoter Region of the β Fibrinogen Gene Is Associated with Plasma Fibrinogen Levels in Smokers and Non-Smokers

We investigated the association between fibrinogen levels and a HaeIII restriction fragment length polymorphism located at −453 bp from the start of transcription of the β fibrinogen gene. 292 healthy men aged 45 to 69 years, recruited from general practices throughout Britain, were studied. None had a history of ischaemic heart disease. 41.1% (120) were smokers and fibrinogen levels were higher in this group. The frequency of the noncutting allele (designated H2) was 0.19 and was the same in smokers and non-smokers. The H2 allele was associated with elevated levels of fibrinogen in both smokers and non-smokers and the effect of genotype was similar in both groups. After smoking, HaeIII genotype was the strongest predictor of fibrinogen levels and explained 3.1% of the variance in fibrinogen levels. These results confirm earlier studies that variation at the fibrinogen locus contributes to the between-individual differences in plasma fibrinogen level.

Effects of Low Intensity Antithrombotic Regimes on the Haemoglobin Level

The effects on the haemoglobin level of low dose aspirin and of low intensity oral anticoagulation with warfarin separately and in combination have been established in men aged between 45 and 69 at high risk of ischaemic heart disease. The findings confirm that combined treatment with warfarin and aspirin (WA) leads to a clear excess of minor bleeding episodes over warfarin alone (W) or aspirin alone (A). Each separate treatment on its own (either W or A) leads to an increase in these episodes compared with those on placebo (P) treatment. However, neither combined treatment (WA) nor the separate treatments (W or A) cause a fall in haemoglobin levels over a period of up to two years.

Extra-Cranial Bleeding and Other Symptoms due to Low Dose Aspirin and Low Intensity Oral Anticoagulation

Data from the early stages of the thrombosis prevention trial (TPT) have been used to establish and quantify the risk of extracranial bleeding due to low dose aspirin (75 mg) and low intensity oral anticoagulation with warfarin (international normalised ratio, INR, 1.5) singly or in combination, in men aged between 45 and 69 who are at high risk of ischaemic heart disease (IHD). The design of the trial is factorial, the four treatments being combined low dose aspirin and low intensity anticoagulation (WA), low intensity anticoagulation alone (W), low dose aspirin alone (A) and double placebo treatment (P). The trial is being carried out through the Medical Research Council’s General Practice Research Framework, with participating practices throughout the United Kingdom. Results are based on the first 3,667 men entered. The risk of major gastrointestinal bleeding due to active treatment is probably about 1 in 500 man-years of treatment, there currently being no difference between the three active regimes (WA, W, A). Intermediate and minor bleeding episodes occur more frequently with WA than with W or A on their own, the excess being mainly due to minor nose bleeds and bruises. In turn, both W and A on their own cause more such minor episodes than placebo treatment, P. There is no evidence that any of the three active regimes increases the risk of peptic ulceration, nor do they increase reports of indigestion. Aspirin increases reports of constipation and reduces reports of blurred vision. Minor bleeding occurs less frequently in smokers than in non-smokers but is not influenced by age. The antithrombotic regimes used are feasible and acceptable. So far, combined treatment and treatment with warfarin alone are not associated with more frequent serious hazards than low dose aspirin on its own, a regime that is increasingly used in clinical practice. The results provide a measure of reassurance for further trials of low intensity oral anticoagulation with warfarin alone or in combination with low dose aspirin.

Methods and Problems of a Stroke Rehabilitation Trial

There are conflicting views on the effectiveness of rehabilitation after stroke; several studies have attempted to compare progress following intensive therapy with that following community care1–6 or no formal treatment,7–9 but for a number of reasons the evidence is inconclusive. Consequently, we have been engaged in a randomised controlled trial of the effectiveness of different intensities of out-patient rehabilitation following stroke. This paper outlines the design, methods and problems of the study.

Building the pipeline: the creation of a residency training pathway for future physician leaders in health care quality

PROBLEM

Many health care organizations seek physicians to lead quality improvement (QI) efforts, yet struggle to find individuals with the necessary expertise. Although most residency programs incorporate QI and patient safety principles into their curricula, few provide a specialized training program for residents exploring careers as physician leaders in quality.

APPROACH

Recognizing this training void, the authors designed and implemented the Healthcare Leadership in Quality (HLQ) track for residents at the University of Pennsylvania Health System in 2010. This longitudinal, two-year graduate medical education (GME) track aligns with the quality goals of the University of Pennsylvania Health System and includes a core curriculum, integration into an interprofessional health care leadership team that is accountable for quality and safety outcomes on a hospital unit, a capstone QI project, and mentorship.

OUTCOMES

Early evaluation has demonstrated the feasibility and efficacy of the track diverse graduate medical education training programs. Using Yardley and Dornan's interpretation of the Kirkpatrick framework, the authors have demonstrated the track's impact on four levels of educational and organizational outcomes.

NEXT STEPS

Building on their early experiences, the authors are integrating project and time management skills into the core curriculum, and they are focusing more effort on faculty development in QI mentorship. Additionally, the authors plan to follow HLQ track graduates to determine whether they seek leadership roles in quality and safety and to assess the influence of the program on their careers.

Politically Incorrect: Legislation Must Not Mandate Specific Healthcare Epidemiology and Infection Prevention and Control Practices

In this issue of the journal, Dr. Farr offers his perspective on the recent position statement from the Joint SHEA and APIC Task Force regarding legislative mandates for use of active surveillance cultures to screen for methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). The position statement specifically addresses the issue of whether the use of MRSA and VRE surveillance cultures in healthcare settings should be mandated by legislation. It does not attempt to address whether or not, when, or for whom active surveillance cultures should be performed. A broad range of experts and the Boards of Directors of the Society for Healthcare Epidemiology (SHEA) and the Association of Professionals in Infection Control (APIC) reviewed this position statement, which summarizes the effectiveness of active surveillance culturing as it pertains to potential legislation. Both Boards agree the position statement represents a well-reasoned, systematic, and fair review of the literature. Of course, no single document, group, or individual should ever be viewed as having the final word on this or any subject. Thoughtful debate regarding the scientific evidence, when conducted in a professional and constructive manner, is a critical and necessary step in the translation of research and clinical observations into bedside practices. Such debate should also lead to a research agenda that will help fill gaps in knowledge that become apparent in the discussion.

The Mortality Review Committee: a novel and scalable approach to reducing inpatient mortality

BACKGROUND

Despite the importance of reducing inpatient mortality, little has been reported about establishing a hospitalwide, systematic process to review and address inpatient deaths. In 2006 the University of Pennsylvania Health System's Mortality Review Committee was established and charged with reducing inpatient mortality as measured by the mortality index--observed/expected mortality.

METHODS

Between 2006 and 2012, through interdisciplinary meetings and analysis of administrative data and chart reviews, the Mortality Review Committee identified a number of opportunities for improvement in the quality of patient care. Several programmatic interventions, such as those aimed at improving sepsis and delirium recognition and management, were initiated through the committee.

RESULTS

During the committee's first six years of activity, the University HealthSystem Consortium (UHC) mortality index decreased from 1.08 to 0.53, with observed mortality decreasing from 2.45% to 1.62%. Interventions aimed at improving sepsis management implemented between 2007 and 2008 were associated with increases in severe sepsis survival from 40% to 56% and septic shock survival from 42% to 54%. The mortality index for sepsis decreased from 2.45 to 0.88. Efforts aimed at improving delirium management implemented between 2008 and 2009 were associated with an increase in the proportion of patients receiving a "timely" intervention from 18% to 57% and with a twofold increase in the percentage of patients discharged to home.

DISCUSSION

The establishment of a mortality review committee was associated with a significant reduction in the mortality index. Keys to success include interdisciplinary membership, partnerships with local providers, and a multipronged approach to identifying important clinical opportunities and to implementing effective interventions.

Ensuring rational public reporting systems for health care-associated infections: systematic literature review and evaluation recommendations

BACKGROUND

The Centers for Disease Control and Prevention (CDC) systematically reviewed published studies for the Healthcare Infection Control Practices Advisory Committee (HICPAC) in preparation for guidance to states on mandatory public reporting systems for health care-associated infections (HAI) in hospitals. The HICPAC asked whether public reporting systems are effective in improving health care performance, by measured improvements in clinical processes or patients' health status as the intended outcomes, including but not limited to reduced HAI events; and whether new evidence of effectiveness of private reporting policies to reduce HAI had been published since the 1970s landmark Study on the Efficacy of Nosocomial Infection Control study.

METHODS

Public reporting systems are information provided to the public about the quality of health services. Of 450 published papers reviewed using specific inclusion and exclusion criteria, 10 studies qualified for detailed, protocol-based abstractions.

RESULTS

Findings indicate that the evidence for effectiveness for public reporting systems to improve health care performance is inconclusive. No studies have investigated reduction of HAI as an outcome of public reporting.

CONCLUSION

Rigorous evaluation of mandatory public reporting systems for HAI is recommended to ensure that stakeholders' needs are identified and met.

Structure, function, and biogenesis of the cell wall of Mycobacterium tuberculosis

Much of the early structural definition of the cell wall of Mycobacterium spp. was initiated in the 1960s and 1970s. There was a long period of inactivity, but more recent developments in NMR and mass spectral analysis and definition of the M. tuberculosis genome have resulted in a thorough understanding, not only of the structure of the mycobacterial cell wall and its lipids but also the basic genetics and biosynthesis. Our understanding nowadays of cell-wall architecture amounts to a massive "core" comprised of peptidoglycan covalently attached via a linker unit (L-Rha-D-GlcNAc-P) to a linear galactofuran, in turn attached to several strands of a highly branched arabinofuran, in turn attached to mycolic acids. The mycolic acids are oriented perpendicular to the plane of the membrane and provide a truly special lipid barrier responsible for many of the physiological and disease-inducing aspects of M. tuberculosis. Intercalated within this lipid environment are the lipids that have intrigued researchers for over five decades: the phthiocerol dimycocerosate, cord factor/dimycolyltrehalose, the sulfolipids, the phosphatidylinositol mannosides, etc. Knowledge of their roles in "signaling" events, in pathogenesis, and in the immune response is now emerging, sometimes piecemeal and sometimes in an organized fashion. Some of the more intriguing observations are those demonstrating that mycolic acids are recognized by CD1-restricted T-cells, that antigen 85, one of the most powerful protective antigens of M. tuberculosis, is a mycolyltransferase, and that lipoarabinomannan (LAM), when "capped" with short mannose oligosaccharides, is involved in phagocytosis of M. tuberculosis. Definition of the genome of M. tuberculosis has greatly aided efforts to define the biosynthetic pathways for all of these exotic molecules: the mycolic acids, the mycocerosates, phthiocerol, LAM, and the polyprenyl phosphates. For example, we know that synthesis of the entire core is initiated on a decaprenyl-P with synthesis of the linker unit, and then there is concomitant extension of the galactan and arabinan chains while this intermediate is transported through the cytoplasmic membrane. The final steps in these events, the attachment of mycolic acids and ligation to peptidoglycan, await definition and will prove to be excellent targets for a new generation of anti-tuberculosis drugs.

Characterization of virulence, colony morphotype and the glycopeptidolipid of Mycobacterium avium strain 104

SETTING

Members of the Mycobacterium avium complex (MAC) are responsible for mycobacterial disease in children, the aged and in immunocompromised individuals. The complex consists of different species, serovars and morphologic forms that vary in virulence. One isolate of the MAC is currently being sequenced (MAC 104) and was chosen based on its derivation from an AIDS patient and the fact that it could be genetically manipulated.

OBJECTIVE

MAC 104 was therefore analyzed for virulence, colony morphotype and expression of the glycopeptidolipid (GPL) responsible for serotying differences and the rough to smooth morphological switch.

RESULTS

The isolate was found to be virulent in the murine model of low-dose aerosol infection in that it could colonize the lung, proliferate within the tissue and disseminate to other organs. MAC 104 expressed a variety of colony morphotypes, the most prevalent of which were smooth opaque, smooth transparent and rough. All three morphotypes could persist in the lung; however, the transparent and rough morphotypes grew more rapidlyinvivo. The rough morphotype was unusual in that it expressed an atypical form of the GPL usually absent from rough morphotypes.

CONCLUSION

This characterization complements the genome data and confirms that MAC 104 behaves similarly to other MAC isolates.

Thrombosis prevention trial: follow-up study of practical implications

The impact of randomised controlled trials on subsequent practice has only occasionally been assessed. Doing so is particularly necessary when unusual and possibly controversial treatments are being used. The aim of this study was to assess the practical implications of the results of the placebo-controlled primary prevention thrombosis prevention trial, in which the active treatment regimens were combined warfarin and aspirin, warfarin alone, and aspirin alone. Both active agents were given in low doses. Decisions on post-trial management were sought about men who continued with randomly-allocated treatment until the trial ended. The results of the trial appeared to have influenced decisions about future management. While aspirin was clearly the most frequent choice, a regimen involving warfarin was also used for a substantial proportion of men. Prior experience of acceptability, effectiveness, and safety probably played a significant part in decisions to continue with or switch to a warfarin-containing regimen. The findings may provide a measure of reassurance about the value of oral anticoagulation in other settings, particularly atrial fibrillation where, despite the results of trials showing major reductions in stroke, anticoagulation is underused.

The role of the embA and embB gene products in the biosynthesis of the terminal hexaarabinofuranosyl motif of Mycobacterium smegmatis arabinogalactan

The emb genes are conserved among different mycobacteria. In Mycobacterium smegmatis and Mycobacterium tuberculosis, they belong to an operon comprising three genes, embC, embA, and embB. The EmbB protein has been proposed to be the target of ethambutol, a drug which is known to inhibit the synthesis of the arabinan portion of the mycobacterial cell wall arabinogalactan (AG). To further define the role of EmbB protein in arabinan biosynthesis, embA, -B, and -C genes were inactivated individually by homologous recombination in M. smegmatis. All three mutants were viable, and among the three, the slowest growing embB(-) mutant encountered profound morphological changes and exhibited a higher sensitivity to hydrophobic drugs and detergents, presumably due to an increase in cell wall permeability. Furthermore, chemical analyses showed that there was a diminution in the arabinose content of arabinogalactan from the embA(-) and embB(-) mutants. Specifically, in comparison with the wild-type strain, the crucial terminal hexaarabinofuranosyl motif, which is a template for mycolylation, was altered in both embA(-) and embB(-) mutants. Detailed nuclear magnetic resonance studies coupled with enzyme digestion, chromatography, and mass spectrometry analyses revealed that the disaccharide beta-d-Ara(f)-(1-->2)-alpha-d-Ara(f) extension from the 3-position of the 3,5-linked alpha-d-Ara(f) residue is markedly diminished. As a consequence, a linear terminal beta-d-Ara(f)-(1-->2)-alpha-d-Ara(f)-(1-->5)-alpha-d-Ara(f)-(1-->5)-alpha-d-Ara(f) is formed, a motif which is a recognized, nonreducing terminal feature of lipoarabinomannan but not of normal AG. Upon complementation with the embB and embA wild-type genes, the phenotype of the mutants reverted to wild-type, in that normal AG was resynthesized. Our results clearly show that both EmbA and EmbB proteins are involved in the formation of the proper terminal hexaarabinofuranoside motif in AG, thus paving the way for future studies to identify the complete array of arabinosyltransferases involved in the synthesis of mycobacterial cell wall arabinan.

Purification and biochemical characterization of the Mycobacterium tuberculosis beta-ketoacyl-acyl carrier protein synthases KasA and KasB

Mycolic acids are vital components of the Mycobacterium tuberculosis cell wall, and enzymes involved in their formation represent attractive targets for the discovery of novel anti-tuberculosis agents. Biosynthesis of the fatty acyl chains of mycolic acids involves two fatty acid synthetic systems, the multifunctional polypeptide fatty acid synthase I (FASI), which performs de novo fatty acid synthesis, and the dissociated FASII system, which consists of monofunctional enzymes, and acyl carrier protein (ACP) and elongates FASI products to long chain mycolic acid precursors. In this study, we present the initial characterization of purified KasA and KasB, two beta-ketoacyl-ACP synthase (KAS) enzymes of the M. tuberculosis FASII system. KasA and KasB were expressed in E. coli and purified by affinity chromatography. Both enzymes showed activity typical of bacterial KASs, condensing an acyl-ACP with malonyl-ACP. Consistent with the proposed role of FASII in mycolic acid synthesis, analysis of various acyl-ACP substrates indicated KasA and KasB had higher specificity for long chain acyl-ACPs containing at least 16 carbons. Activity of KasA and KasB increased with use of M. tuberculosis AcpM, suggesting that structural differences between AcpM and E. coli ACP may affect their recognition by the enzymes. Both enzymes were sensitive to KAS inhibitors cerulenin and thiolactomycin. These results represent important steps in characterizing KasA and KasB as targets for antimycobacterial drug discovery.

Genomic evidence for the retention of the essential mycobacterial cell wall in the otherwise defective Mycobacterium leprae

The obligate intracellularism of Mycobacterium leprae may be attributable to the effects of mutations in major metabolic areas due to a genome capable of encoding only about 1600 proteins. Yet cell wall biosynthesis capability remains relatively intact and comparisons with the genome of Mycobacterium tuberculosis provide insights into the genetic basis of a minimal mycobacterial cell wall.

Infected branchial cleft cyst due to Bordetella bronchiseptica in an immunocompetent patient

A healthy 23-year-old man with fever and a tender mass in his right anterior neck was found to have a branchial cleft cyst infected with Bordetella bronchiseptica. Initial testing suggested a Brucella species, but further laboratory testing identified the organism definitively. B. bronchiseptica infection in healthy adults is an unusual event.

Biosynthesis of the arabinogalactan-peptidoglycan complex of Mycobacterium tuberculosis

The compositional complexity of the mycobacterial cell envelope differentiates Mycobacterium species from most other prokaryotes. Historically, research in this area has focused on the elucidation of the structure of the mycobacterial cell envelope with the result that the structures of the mycolic acid-arabinogalactan-peptidoglycan complex from M. tuberculosis are fairly well understood. However, the current impetus for studying M. tuberculosis and other pathogenic mycobacteria is the need to identify targets for the development of new drugs. Therefore, emphasis has been shifting to the study of cell envelope biosynthesis and the identification of enzymes that are essential to the viability of M. tuberculosis. The publication of the complete M. tuberculosis genome in 1998 has greatly aided these studies. To date, thirteen enzymes involved in the synthesis of the arabinogalactan-peptidoglycan complex of M. tuberculosis have been identified and at least partially characterized. Eleven of these enzymes were reported subsequent to the publication of the M. tuberculosis genome, a clear indication of the rapid evolution of knowledge stimulated by the sequencing of the genome. In this article we review the current understanding of M. tuberculosis arabinogalactan-peptidoglycan structure and biosynthesis.

Specific and early detection of IgG, IgA and IgM antibodies to Mycobacterium tuberculosis 38kDa antigen in pulmonary tuberculosis

The objective was to apply the purified 38kDa protein antigen of Mycobacterium tuberculosis in ELISA to estimate the IgG, IgA and IgM antibody levels in sera and circulating immune complexes of tuberculosis patients. Sera from smear and culture positive tuberculosis patients were positive for anti 38kDa IgG, IgA and IgM antibodies, with a sensitivity of 61%, 30% and 10%, respectively, and with a specificity of 100% for IgG. The sensitivity of the test improved to a level of 68% for IgG+IgA and of 71.4% for IgG+IgA+IgM without significantly compromising the specificity (IgG of 100%, IgG+IgA of 96%, IgG+IgA+IgM of 90%). Among the smear, culture-negative but X-ray-positive cases, 60% were serum positive for IgG antibody, while in smear-negative but culture-positive cases, 54% were positive for IgG antibody. Measurement of 38kDa antibodies showed a greater than 95% sensitivity in smear and culture-positive, and smear-negative and culture-positive patients, through a combination of assays for serum IgG and circulating immune complex antibodies, while the specificity was 100%.

Mycobacterial lysocardiolipin is exported from phagosomes upon cleavage of cardiolipin by a macrophage-derived lysosomal phospholipase A2

Pathogenic mycobacteria are able to survive and proliferate in phagosomes within host macrophages (Mphi). This capability has been attributed in part to their cell wall, which consists of various unique lipids. Some of these are important in the host-pathogen interaction, such as resistance against microbicidal effector mechanisms and modulation of host cell functions, and/or are presented as Ags to T cells. Here we show that two lipids are released from the mycobacterial cell wall within the phagosome of infected Mphi and transported out of this compartment into intracellular vesicles. One of these lipids was identified as lysocardiolipin. Lysocardiolipin was generated through cleavage of mycobacterial cardiolipin by a Ca2+-independent phospholipase A2 present in Mphi lysosomes. This result indicates that lysosomal host cell enzymes can interact with released mycobacterial lipids to generate new products with a different intracellular distribution. This represents a novel pathway for the modification of bacterial lipid Ags.

The genome of Mycobacterium leprae: a minimal mycobacterial gene set

Comparison of the recently sequenced genome of the leprosy-causing pathogen Mycobacterium leprae with other mycobacterial genomes reveals a drastic gene reduction and decay in M. leprae affecting many metabolic areas, exemplified by the retention of a minimal set of genes required for cell-wall biosynthesis.

Identification of putative exported/secreted proteins in prokaryotic proteomes

The increasing number of bacterial genomes being sequenced fuels an equal demand for methods to rapidly analyze the proteomes of these organisms. One group of proteins of pressing importance is the exported/secreted proteins, given their dominant immunogenicity and role in pathogenesis. With this in mind, a weight matrix algorithm and two artificial neural networks, one based on amino acid position within the N-terminus and the other on amino acid frequency, were developed for identification of such proteins. The neural networks and a hybrid method, combining the weight matrix algorithm and the amino acid frequency neural network, were tested independently against a standard data set of secreted and cytoplasmic proteins to determine their accuracy in predicting secreted prokaryotic proteins. The results of these analyses demonstrated that the amino acid position neural network provided the highest accuracy (Mathews correlation coefficient of 0.93) in predicting secreted proteins of Gram-negative bacteria, whereas the hybrid method was best (Mathews correlation coefficient of 0.97) for prediction of Gram-positive secreted proteins. These two methods were integrated into a single program (ExProt) designed to analyze whole proteomes. In addition to protein localization, ExProt also contains a neural network trained to identify the most probable signal peptidase I cleavage site of secreted proteins. When tested against the standard protein data set ExProt correctly predicted 73.5 and 84.5% of the cleavage sites in Gram-positive and Gram-negative secreted proteins, respectively. Comparative analysis of Gram-negative, Gram-positive, Mycobacterium tuberculosis, and Archaea proteomes with ExProt revealed that the fraction of putative exported/secreted proteins encoded by bacterial genomes ranged from 8% for Methanococcus jannaschii to 37% for Mycoplasma pneumoniae.

Galactan biosynthesis in Mycobacterium tuberculosis. Identification of a bifunctional UDP-galactofuranosyltransferase

The cell wall of Mycobacterium tuberculosis and related genera is unique among prokaryotes, consisting of a covalently bound complex of mycolic acids, D-arabinan and D-galactan, which is linked to peptidoglycan via a special linkage unit consisting of Rhap-(1-->3)-GlcNAc-P. Information concerning the biosynthesis of this entire polymer is now emerging with the promise of new drug targets against tuberculosis. Accordingly, we have developed a galactosyltransferase assay that utilizes the disaccharide neoglycolipid acceptors beta-d-Galf-(1-->5)-beta-D-Galf-O-C(10:1) and beta-D-Galf-(1-->6)-beta-D-Galf-O-C(10:1), with UDP-Gal in conjunction with isolated membranes. Chemical analysis of the subsequent reaction products established that the enzymatically synthesized products contained both beta-D-Galf linkages ((1-->5) and (1-->6)) found within the mycobacterial cell, as well as in an alternating (1-->5) and (1-->6) fashion consistent with the established structure of the cell wall. Furthermore, through a detailed examination of the M. tuberculosis genome, we have shown that the gene product of Rv3808c, now termed glfT, is a novel UDP-galactofuranosyltransferase. This enzyme possesses dual functionality in performing both (1-->5) and (1-->6) galactofuranosyltransferase reactions with the above neoglycolipid acceptors, using membranes isolated from the heterologous host Escherichia coli expressing Rv3808c. Thus, at a biochemical and genetic level, the polymerization of the galactan region of the mycolyl-arabinogalactan complex has been defined, allowing the possibility of further studies toward substrate recognition and catalysis and assay development. Ultimately, this may also lead to a more rational approach to drug design to be explored in the context of mycobacterial infections.

Expression, purification, and characterization of the Mycobacterium tuberculosis acyl carrier protein, AcpM

Mycolic acids are generated in Mycobacterium tuberculosis as a result of the interaction of two fatty acid biosynthetic systems: the multifunctional polypeptide, FASI, in which the acyl carrier protein (ACP) domain forms an integral part of the polypeptide, and the dissociated FASII system, which is composed of monofunctional enzymes and a discrete ACP (AcpM). In order to characterize enzymes of the FASII system, large amounts of AcpM are required to generate substrates such as holo-AcpM, malonyl-AcpM and acyl-AcpM. The M. tuberculosis acpM gene was overexpressed in Escherichia coli and AcpM purified, yielding approximately 15-20 mg/l of culture. Analysis of AcpM by mass spectrometry, N-terminal sequencing, amino acid analysis, and gas chromatography indicated the presence of three species, apo-, holo-, and acyl-AcpM, the former comprising up to 65% of the total pool. The apo-AcpM was purified away from the in vivo generated holo- and acyl-forms, which were inseparable and heterogeneous with respect to acyl chain lengths. Once purified, we were able to convert apo-AcpM into holo- and acyl-forms. These procedures provide the means for the preparation of the large quantities of AcpM and derivatives needed for characterization of the purified enzymes of the mycobacterial FASII system.

Biochemical characterization of acyl carrier protein (AcpM) and malonyl-CoA:AcpM transacylase (mtFabD), two major components of Mycobacterium tuberculosis fatty acid synthase II

Malonyl coenzyme A (CoA)-acyl carrier protein (ACP) transacylase (MCAT) is an essential enzyme in the biosynthesis of fatty acids in all bacteria, including Mycobacterium tuberculosis. MCAT catalyzes the transacylation of malonate from malonyl-CoA to activated holo-ACP, to generate malonyl-ACP, which is an elongation substrate in fatty acid biosynthesis. To clarify the roles of the mycobacterial acyl carrier protein (AcpM) and MCAT in fatty acid and mycolic acid biosynthesis, we have cloned, expressed, and purified acpM and mtfabD (malonyl-CoA:AcpM transacylase) from M. tuberculosis. According to the culture conditions used, AcpM was produced in Escherichia coli in two or three different forms: apo-AcpM, holo-AcpM, and palmitoylated-AcpM, as revealed by electrospray mass spectrometry. The mtfabD gene encoding a putative MCAT was used to complement a thermosensitive E. coli fabD mutant. Expression and purification of mtFabD resulted in an active enzyme displaying strong MCAT activity in vitro. Enzymatic studies using different ACP substrates established that holo-AcpM constitutes the preferred substrate for mtFabD. In order to provide further insight into the structure-function relationship of mtFabD, different mutant proteins were generated. All mutations (Q9A, R116A, H194A, Q243A, S91T, and S91A) completely abrogated MCAT activity in vitro, thus underlining the importance of these residues in transacylation. The generation and characterization of the AcpM forms and mtFabD opens the way for further studies relating to fatty acid and mycolic acid biosynthesis to be explored in M. tuberculosis. Since a specific type of FabD is found in mycobacterial species, it represents an attractive new drug target waiting to be exploited.

Purification, enzymatic characterization, and inhibition of the Z-farnesyl diphosphate synthase from Mycobacterium tuberculosis

We have recently shown that open reading frame Rv1086 of the Mycobacterium tuberculosis H37Rv genome sequence encodes a unique isoprenyl diphosphate synthase. The product of this enzyme, omega,E,Z-farnesyl diphosphate, is an intermediate for the synthesis of decaprenyl phosphate, which has a central role in the biosynthesis of most features of the mycobacterial cell wall, including peptidoglycan, arabinan, linker unit galactan, and lipoarabinomannan. We have now purified Z-farnesyl diphosphate synthase to near homogeneity using a novel mycobacterial expression system. Z-Farnesyl diphosphate synthase catalyzed the addition of isopentenyl diphosphate to omega,E-geranyl diphosphate or omega,Z-neryl diphosphate yielding omega,E,Z-farnesyl diphosphate and omega,Z,Z-farnesyl diphosphate, respectively. The enzyme has an absolute requirement for a divalent cation, an optimal pH range of 7-8, and K(m) values of 124 micrometer for isopentenyl diphosphate, 38 micrometer for geranyl diphosphate, and 16 micrometer for neryl diphosphate. Inhibitors of the Z-farnesyl diphosphate synthase were designed and chemically synthesized as stable analogs of omega,E-geranyl diphosphate in which the labile diphosphate moiety was replaced with stable moieties. Studies with these compounds revealed that the active site of Z-farnesyl diphosphate synthase differs substantially from E-farnesyl diphosphate synthase from pig brain (Sus scrofa).

Further biochemical characterization of Mycobacterium leprae laminin-binding proteins

It has been demonstrated that the alpha2 chain of laminin-2 present on the surface of Schwann cells is involved in the process of attachment of Mycobacterium leprae to these cells. Searching for M. leprae laminin-binding molecules, in a previous study we isolated and characterized the cationic proteins histone-like protein (Hlp) and ribosomal proteins S4 and S5 as potential adhesins involved in M. leprae-Schwann cell interaction. Hlp was shown to bind alpha2-laminins and to greatly enhance the attachment of mycobacteria to ST88-14 Schwann cells. In the present study, we investigated the laminin-binding capacity of the ribosomal proteins S4 and S5. The genes coding for these proteins were PCR amplified and their recombinant products were shown to bind alpha2-laminins in overlay assays. However, when tested in ELISA-based assays and in adhesion assays with ST88-14 cells, in contrast to Hlp, S4 and S5 failed to bind laminin and act as adhesins. The laminin-binding property and adhesin capacity of two basic host-derived proteins were also tested, and only histones, but not cytochrome c, were able to increase bacterial attachment to ST88-14 cells. Our data suggest that the alanine/lysine-rich sequences shared by Hlp and eukaryotic H1 histones might be involved in the binding of these cationic proteins to laminin.

Induction of inducible nitric oxide synthase-NO* by lipoarabinomannan of Mycobacterium tuberculosis is mediated by MEK1-ERK, MKK7-JNK, and NF-kappaB signaling pathways

Nitric oxide (NO*) expression by inducible nitric oxide synthase (iNOS) is an important host defense mechanism against Mycobacterium tuberculosis in mononuclear phagocytes. The objective of this investigation was to examine the role of mitogen-activated protein (MAP) kinase (MAPK) and nuclear factor kappaB (NF-kappaB) signaling pathways in the regulation of iNOS and NO* by a mycobacterial cell wall lipoglycan known as mannose-capped lipoarabinomannan (ManLAM). Specific pharmacologic inhibition of the extracellular-signal-regulated kinase (ERK) or NF-kappaB pathway revealed that both these signaling cascades were required in gamma interferon (IFN-gamma)-ManLAM-induced iNOS protein and NO2- expression in mouse macrophages. Transient cotransfection of dominant-negative protein mutants of the c-Jun NH2-terminal kinase (JNK) pathway revealed that the MAP kinase kinase 7 (MKK7)-JNK cascade also mediated IFN-gamma-ManLAM induction of iNOS promoter activity whereas MKK4 did not. Overexpression of null mutant IkappaBalpha, a potent inhibitor of NF-kappaB activation, confirmed that the IkappaBalpha kinase (IKK)-NF-kappaB signaling pathway enhanced IFN-gamma-ManLAM-induced iNOS promoter activity. By contrast, activated p38mapk inhibited iNOS induction. These results indicate that combined IFN-gamma and ManLAM stimulation induced iNOS and NO. expression and that MEK1-ERK, MKK7-JNK, IKK-NF-kappaB, and p38mapk signaling pathways play important regulatory roles.

Synthetic mannosides act as acceptors for mycobacterial α1-6 mannosyltransferase

A series of synthetic mannosides was screened in a cell-free system for their ability to act as acceptor substrates for mycobacterial mannosyltransferases. Evaluation of these compounds demonstrated the incorporation of [14C]Man from GDP-[14C]Man into a radiolabeled organic-soluble fraction and analysis by thin layer chromatography and autoradiography revealed the formation of two radiolabeled products. Each synthetic acceptor was capable of accepting one or two mannose residues, resulting in a major and a minor mannosylated product. Both products from each acceptor were isolated and their mass was confirmed by fast-atom bombardment-mass spectrometry (FABMS). Characterization of each mannosylated product by exo-glycosidase digestion. acetolysis and linkage analysis by gas chromatography mass spectrometry of partially per-O-methylated alditols, revealed only alpha1-6-linked products. In addition. the antibiotic amphomycin selectively inhibited the formation of mannosylated products suggesting polyprenolmonophosphate-mannose (C15 50-P-Man) was the immediate mannose donor in all mannosylation reactions observed. The ability of synthetic disaccharides to act as acceptor substrates in this system, is most likely due to the action of a mycobacterial polyprenol-P-Man:mannan alpha1-6 mannosyltransferase involved in the biosynthesis of linear alpha1-6-linked lipomannan.

Interleukin-1 or tumor necrosis factor-alpha augmented the cytotoxic effect of mycobacteria on human fibroblasts: application to evaluation of pathogenesis of clinical isolates of Mycobacterium tuberculosis and M. avium complex

Mycobacteria-induced in vitro events reflecting human tuberculosis can contribute to the evaluation of the pathogenesis of Mycobacterium tuberculosis (MTB). In this study, we propose such an in vitro method based on live mycobacteria-induced cytotoxicity to human cell lines. When human lung-derived normal fibroblast cell line MRC-5 was infected with various strains of mycobacteria (M. tuberculosis H(37)Rv and H(37) Ra, Mycobacterium avium 427S and 2151SmO, and Mycobacterium bovis BCG Pasteur and Tokyo), the fibroblasts were killed by mycobacteria according to the degree of virulence. Other human originated macrophage (U-937, THP-1), myeloid (HL-60), and epithelial carcinoma (A549) cell lines exhibited a similar cytotoxic response to virulent mycobacteria. MRC-5 was most susceptible to virulent mycobacteria among various human cell lines examined. The cytotoxicity was enhanced by the proinflammatory cytokines, interleukin-1 (IL-1) and tumor necrosis factor-a (TNF-alpha), which in the absence of mycobacteria stimulate the growth of normal human fibroblasts. This in vitro evaluation system was applied to clinical isolates of drug-sensitive MTB (DS-MTB), drug-resistant MTB (DR-MTB) including multidrug-resistant (MDR-MTB), and M. avium complex (MAC). MTB strains (n = 24) exhibited strong cytotoxic activity, but MAC strains (n = 5) had only weak activity. Furthermore, there was no significant difference in cytotoxicity between DS-MTB (n = 11) and DR-MTB (n = 13). Collectively, these results suggest that this new in vitro system is useful for evaluating the pathogenesis of mycobacteria and that there was no difference in the pathogenesis between drug-susceptible and drug-resistant clinical isolates.

Cell-mediated immune response to tuberculosis antigens: comparison of skin testing and measurement of in vitro gamma interferon production in whole-blood culture

Although delayed-type hypersensitivity skin testing with tuberculin purified protein derivative (PPD) is the standard for tuberculosis screening, its variability suggests the need for a more sensitive, noninvasive test. An in vitro whole-blood assay has been proposed as an alternative. Using health care worker volunteers, we confirmed the correlation between PPD skin test (PPD-ST) results (positive, induration of >15 mm) and a standardized gamma interferon (IFN-gamma) assay, QuantiFERON-TB (Q-IFN), manufactured by CSL Biosciences in Australia, and we evaluated Mycobacterium tuberculosis culture subfractions as potential substitutes for PPD. Twenty healthy volunteers with positive PPD-ST results and 20 PPD-ST-negative controls were enrolled. Whole blood was cultured with human PPD antigens (HuPPD), Mycobacterium avium complex (MAC) PPD, phytohemagglutinin (PHA), and four M. tuberculosis culture subfractions: low-molecular-weight culture, filtrate, culture filtrate without lipoarabinomannan, soluble cell wall proteins, and cytosolic proteins, all developed from M. tuberculosis strain H(37)RV. Secretion of IFN-gamma (expressed as international units per milliliter) was measured by an enzyme immunoassay. The PPD or subculture fraction response as a percentage of the PHA response was used to determine positivity. Sixteen of 20 PPD-ST-positive individuals were classified as M. tuberculosis positive by Q-IFN, and 1 was classified as MAC positive. Sixteen of 20 PPD-ST-negative individuals were M. tuberculosis negative by Q-IFN, 2 were MAC positive, and 2 were M. tuberculosis positive. The tuberculosis culture subfractions stimulated IFN-gamma production in PPD-ST-positive volunteers, and significant differences could be seen between the two PPD-ST groups with all subfractions except soluble cell wall protein; however, the response was variable and no better than the Q-IFN PPD. The agreement between the Q-IFN test and the PPD-ST was good (Cohen's kappa = 0.73). The Q-IFN assay can be a useful tool in further studies of immune responses to M. tuberculosis antigens.

Binding of alpha2-laminins by pathogenic and non-pathogenic mycobacteria and adherence to Schwann cells

The ability of Mycobacterium leprae to specifically bind alpha2-laminins of Schwann cells has been described recently as being an important property of the leprosy bacillus, which could explain the neural tropism of M. leprae. Therefore, the extent of the expression of alpha2-laminin-binding properties among mycobacteria was investigated. In an ELISA-based assay, all three species of Mycobacterium tested (M. tuberculosis, M. chelonae and M. smegmatis) expressed laminin-binding capacity, suggesting that the ability to bind alpha2-laminins is conserved within the genus Mycobacterium. This report also demonstrated that not only M. leprae but all the mycobacterial species tested readily interacted with the ST88-14 cells, a human schwannoma cell line, and that the addition of soluble alpha2-laminins significantly increased their adherence to these cells. These results failed to demonstrate the presence in M. leprae of a unique system based on alpha2-laminins for adherence to Schwann cells.

Detection of phenolic glycolipid I of Mycobacterium leprae in sera from leprosy patients before and after start of multidrug therapy

A total of 100 untreated new leprosy patients were recruited prospectively and examined for the presence of phenolic glycolipid I (PGL-I) antigen in their serum specimens by dot enzyme-linked immunosorbent assay (ELISA) using rabbit anti-PGL-I antiserum. The presence of circulating PGL-I antigen was closely related to the bacterial indices (BI) of the patients. The PGL-I antigen was detectable in 27 (93.1%) of 29 patients with a BI of 4.0 or above and in 15 (68.2%) of 22 patients with a BI of 3.0 to 3.9. However, none of the 37 patients with a BI of less than 1.9 had detectable PGL-I antigen by the methods used in this study. The level of PGL-I in serum declined rapidly by about 90% 1 month after the start of multidrug therapy. This study showed clearly that anti-PGL-I IgM antibodies and circulating PGL-I antigen levels reflect the bacterial loads in untreated leprosy patients. The serological parameters based on the PGL-I antigen may therefore be useful in the assessment of leprosy patients at the time of diagnosis and possibly in monitoring patients following chemotherapy.

Comparison of the UDP-N-acetylmuramate:L-alanine ligase enzymes from Mycobacterium tuberculosis and Mycobacterium leprae

In the peptidoglycan of Mycobacterium leprae, L-alanine of the side chain is replaced by glycine. When expressed in Escherichia coli, MurC (UDP-N-acetyl-muramate:L-alanine ligase) of M. leprae showed K(m) and V(max) for L-alanine and glycine similar to those of Mycobacterium tuberculosis MurC, suggesting that another explanation should be sought for the presence of glycine.

Skin test development in leprosy: progress with first-generation skin test antigens, and an approach to the second generation

One of the most urgent needs from leprosy research is a test for infection. The lepromin test is not suitable as a diagnostic test for leprosy, and neither the Rees nor the Convit soluble antigens has appeared sufficiently specific. Because two new antigens, MLSA-LAM and MLCwA, may not fully meet the requirements for specificity, we have embarked upon the preparation of a second generation of skin test antigens. Size-fractionated cryptozoic proteins were prepared from M. leprae by electroelution from preoperative sodium dodecylsulphate-polyacrylamide gel electrophoresis, and individual fractions were probed with polyclonal and monoclonal antibody reagents to identify both known and novel proteins. In addition, immunological responses were assessed in M. leprae-sensitized guinea pigs against both crude subcellular fractions (cytosol, membrane, and soluble cell wall proteins) and the size-fractionated cytosolic proteins. A particularly promising subcellular fraction is the membrane fraction of M. leprae, which contains many proteins unique to the organism. Clinical trials of the M. leprae membrane proteins are now being planned.

Role of the cell wall phenolic glycolipid-1 in the peripheral nerve predilection of Mycobacterium leprae

The cell wall of pathogenic mycobacteria is abundant with complex glycolipids whose roles in disease pathogenesis are mostly unknown. Here, we provide evidence for the involvement of the specific trisaccharide unit of the phenolic glycolipid-1 (PGL-1) of Mycobacterium leprae in determining the bacterial predilection to the peripheral nerve. PGL-1 binds specifically to the native laminin-2 in the basal lamina of Schwann cell-axon units. This binding is mediated by the alpha(2LG1, alpha2LG4, and alpha2LG5 modules present in the naturally cleaved fragments of the peripheral nerve laminin alpha2 chain, and is inhibited by the synthetic terminal trisaccharide of PGL-1. PGL-1 is involved in the M. leprae invasion of Schwann cells through the basal lamina in a laminin-2-dependent pathway. The results indicate a novel role of a bacterial glycolipid in determining the nerve predilection of a human pathogen.

Biosynthesis of the galactan component of the mycobacterial cell wall

The structural core of the cell walls of Mycobacterium spp. consists of peptidoglycan bound by a linker unit (-alpha-L-Rhap-(1-->3)-D-GlcNAc-P-) to a galactofuran, which in turn is attached to arabinofuran and mycolic acids. The sequence of reactions leading to the biogenesis of this complex starts with the formation of the linker unit on a polyprenyl-P to produce polyprenyl-P-P-GlcNAc-Rha (Mikusová, K., Mikus, M., Besra, G. S., Hancock, I., and Brennan, P. J. (1996) J. Biol. Chem. 271, 7820-7828). We now establish that formation of the galactofuran takes place on this intermediate with UDP-Galf as the Galf donor presented in the form of UDP-Galp and UDP-Galp mutase (the glf gene product) and is catalyzed by galactofuranosyl transferases, one of which, the Mycobacterium tuberculosis H37Rv3808c gene product, has been identified. Evidence is also presented for the growth of the arabinofuran on this polyprenyl-P-P-linker unit-galactan intermediate catalyzed by unidentified arabinosyl transferases, with decaprenyl-P-Araf or 5-P-ribosyl-PP as the Araf donor. The product of these steps, the lipid-linked-LU-galactan-arabinan has been partially characterized in terms of its heterogeneity, size, and composition. Biosynthesis of the major components of mycobacterial cell walls is proving to be extremely complex. However, partial definition of arabinogalactan synthesis, the site of action of several major anti-tuberculosis drugs, facilitates the present day thrust for new drugs to counteract multiple drug-resistant tuberculosis.

Bacterial and host-derived cationic proteins bind alpha2-laminins and enhance Mycobacterium leprae attachment to human Schwann cells

It has recently been demonstrated that laminin alpha2 chains present on the surface of Schwann cells are involved in the process of attachment of Mycobacterium leprae to these cells. In this study, a protein in the M. leprae cell wall that was found to be capable of binding alpha2-containing laminins (merosin) was isolated and characterized. The M. leprae laminin-binding protein was identified as a 21-kDa histone-like protein (Hlp), a highly conserved cationic protein present in other species of mycobacteria. The gene that encodes this protein was PCR amplified, cloned, and expressed, and the recombinant protein was shown to bind alpha2-laminins. More significantly, when added exogenously, Hlp was able to greatly enhance the attachment of mycobacteria to ST88-14 human Schwann cells. The capacity to bind alpha2-laminins and to enhance mycobacterial adherence to Schwann cells was also found in other cationic proteins such as host-derived histones. Moreover, mutation in the hlp gene was shown not to affect the capacity of mycobacteria to bind to ST88-14 cells, suggesting that alternative adhesins and/or pathways might be used by mycobacteria during the process of adherence to Schwann cells. The potential role of Hlp as a fortuitous virulence factor contributing to the pathogenesis of M. leprae-mediated nerve damage is discussed.

Polyprenyl phosphate biosynthesis in Mycobacterium tuberculosis and Mycobacterium smegmatis

Mycobacterium smegmatis has been shown to contain two forms of polyprenyl phosphate (Pol-P), while Mycobacterium tuberculosis contains only one. Utilizing subcellular fractions from M. smegmatis and M. tuberculosis, we show that Pol-P synthesis is different in these species. The specific activities of the prenyl diphosphate synthases in M. tuberculosis are 10- to 100-fold lower than those in M. smegmatis. In M. smegmatis decaprenyl diphosphate and heptaprenyl diphosphate were the main products synthesized in vitro, whereas in M. tuberculosis only decaprenyl diphosphate was synthesized. The data from both organisms suggest that geranyl diphosphate is the allylic substrate for two distinct prenyl diphosphate synthases, one located in the cell membrane that synthesizes omega,E,Z-farnesyl diphosphate and the other present in the cytosol that synthesizes omega,E,E,E-geranylgeranyl diphosphate. In M. smegmatis, the omega,E, Z-farnesyl diphosphate is utilized by a membrane-associated prenyl diphosphate synthase activity to generate decaprenyl diphosphate, and the omega,E,E,E-geranylgeranyl diphosphate is utilized by a membrane-associated activity for the synthesis of the heptaprenyl diphosphate. In M. tuberculosis, however, omega,E,E,E-geranylgeranyl diphosphate is not utilized for the synthesis of heptaprenyl diphosphate. Thus, the difference in the compositions of the Pol-P of M. smegmatis and M. tuberculosis can be attributed to distinct enzymatic differences between these two organisms.

Phosphatidylinositol is an essential phospholipid of mycobacteria

Phosphatidylinositol (PI) and metabolically derived products such as the phosphatidylinositol mannosides and linear and mature branched lipomannan and lipoarabinomannan are prominent phospholipids/lipoglycans of Mycobacterium sp. believed to play important roles in the structure and physiology of the bacterium as well as during host infection. To determine if PI is an essential phospholipid of mycobacteria, we identified the pgsA gene of Mycobacterium tuberculosis encoding the phosphatidylinositol synthase enzyme and constructed a pgsA conditional mutant of Mycobacterium smegmatis. The ability of this mutant to synthesize phosphatidylinositol synthase and subsequently PI was dependent on the presence of a functional copy of the pgsA gene carried on a thermosensitive plasmid. The mutant grew like the control strain under permissive conditions (30 degrees C), but ceased growing when placed at 42 degrees C, a temperature at which the rescue plasmid is lost. Loss of cell viability at 42 degrees C was observed when PI and phosphatidylinositol dimannoside contents dropped to approximately 30 and 50% of the wild-type levels, respectively. This work provides the first evidence of the essentiality of PI to the survival of mycobacteria. PI synthase is thus an essential enzyme of Mycobacterium that shows promise as a drug target for anti-tuberculosis therapy.

Minimum effective intensity of oral anticoagulant therapy in primary prevention of coronary heart disease

BACKGROUND

There is mounting evidence that low-intensity oral anticoagulation is effective, particularly in primary prevention of thrombosis, with important implications for safety and the practicalities of using warfarin. Because it is desirable to know possible benefits for different indications so that optimal therapy can be administered in as wide a range of conditions as possible, we analyzed data from the Thrombosis Prevention Trial, a factorial trial that compared treatment with low-intensity, dose-adjusted warfarin and low-dose aspirin separately and together, to determine the minimum effective intensity of oral anticoagulation in the primary prevention of coronary heart disease.

METHODS

The international normalized ratio (INR) most recent to an event and overall time at each INR were used to calculate the INR-related event rate for coronary events, strokes, and major and minor bleeding episodes in 2545 men receiving warfarin with or without aspirin (75 mg/d) and followed up for a total of 9952 person-years.

RESULTS

Compared with placebo, warfarin alone at a dose that maintained the INR at 1.4 or more significantly reduced the risk of a coronary event by 47% (95% confidence interval, 4%-70%; P =.03), whereas the risk of a coronary event was not reduced at INRs below 1. 4. Coronary events, strokes, and major bleeding episodes combined were significantly reduced by 45% (95% confidence interval, 9%-67%; P =.02) in the warfarin group compared with the placebo group when the INR was 1.4 or more. Minor bleeding episodes increased as the INR rose above about 2.0. No significant association of INR with coronary events was observed with combined warfarin and aspirin, possibly reflecting the small number of such events that occurred in this group, therefore limiting the power to detect an association with INR.

CONCLUSIONS

Warfarin alone is effective in the primary prevention of coronary heart disease when the dose is adjusted to maintain an INR of 1.4 or more. The results add to the evidence that low-intensity, dose-adjusted oral anticoagulation is effective for a range of conditions.