Expression of the naphthoate synthase gene in Mycobacterium tuberculosis in a self-generated oxygen depleted liquid culture system.

Mycobacterium tuberculosis has been classified for decades as a strict aerobic species. Whole genome sequencing of the type culture strain H37Rv has revealed the presence of a full set of genes allowing for anaerobic metabolism. Naphthoate synthase (menB) is a key enzyme required for the synthesis of menaquinone, which plays a crucial role in anaerobic electron transport, ultimately resulting in the formation of energy generating intermediates. Interrupting the synthesis of this enzyme will interfere with the production of menaquinone and therefore this enzyme is a potential drug target. This study serves to investigate the role of naphtoate synthase in the survival of M. tuberculosis H37Rv when incubated under oxygen limiting conditions of unagitated liquid culture over 15 weeks. M. tuberculosis H37Rv was grown in Middlebrook 7H9 media. The tubes were kept undisturbed at 37 °C for up to 15 weeks. At selected time points, aliquots of cells were removed and frozen. RNA was simultaneously extracted from all aliquots. The RNA was converted to cDNA for Real-Time PCR on the ABI 7000 SDS. Gene expression was normalized against 16S RNA quantities at each time point. A systematic increase in the expression of the menB gene product was observed over the incubation period with a 4.3-fold increase seen at week 6 (P < 0.001) relative to day 0 and an 85.8-fold increase at week 15 (P < 0.001) relative to day 0. Cells of M. tuberculosis increase menaquinone production during prolonged incubation in broth culture as a mechanism of survival. This study substantiates the menB enzyme to be a putative drug target.

Evaluation of time to detection of Mycobacterium tuberculosis in broth culture as a determinant for end points in treatment trials.

Time to detection of Mycobacterium tuberculosis in broth culture was examined for utility as a treatment efficacy end point. Of 146 patients in a phase IIB trial, a decreased mean time to detection was found in 5 with treatment failure. Time to detection in an analysis-of-covariance model was associated with lung cavities, less intensive treatment, and differences in the bactericidal effects of treatment regimens.

A Phase II study of the sterilising activities of ofloxacin, gatifloxacin and moxifloxacin in pulmonary tuberculosis.

SETTING: Current treatment for pulmonary tuberculosis (TB) might be shortened by the incorporation of fluoroquinolones (FQs). OBJECTIVES: A Phase II study aimed to assess the sterilising activities of three novel regimens containing FQs before a Phase III trial of a 4-month regimen containing gatifloxacin (GFX). DESIGN: A total of 217 newly diagnosed smear-positive patients were randomly allocated to one of four regimens: isoniazid (INH), pyrazinamide and rifampicin (RMP) with either ethambutol, GFX, moxifloxacin (MFX) or ofloxacin (OFX) for 2 months. At the end of the study, RMP and INH were given for 4 months. The rates of elimination of Mycobacterium tuberculosis were compared in the regimens using non-linear mixed effects modelling of the serial sputum colony counts (SSCC) during the first 8 weeks. RESULTS: After adjustment for covariates, MFX substitution appeared superior during the early phase of a bi-exponential fall in colony counts, but significant and similar acceleration of bacillary elimination during the late phase occurred with both GFX and MFX (P = 0.002). Substitution of OFX had no effect. These findings were supported by estimates of time to conversion, using Cox regression, but there were no significant differences in proportions culture-negative at 8 weeks. CONCLUSIONS: GFX and MFX improve the sterilising activity of regimens and might shorten treatment; their progression into Phase III trials therefore seems warranted.

Lower dose of ciprofloxacin is adequate for the treatment of Neisseria gonorrhoeae in KwaZulu Natal, South Africa.

The response of male gonococcal urethritis to a single 250 mg dose of ciprofloxacin versus 500 mg was studied. Both regimens were given in combination with doxycycline in the context of the local syndromic management protocol. There was no significant difference in response between the regimens, inclusive/exclusive of tetracycline susceptible isolates. One patient in the 250 mg arm failed to respond clinically but was microbiologically cured and four patients in the 500 mg arm failed microbiologically but responded clinically. All four isolates had ciprofloxacin MICs

Evolution in the trends of antimicrobial resistance in Neisseria gonorrhoeae isolated in Durban over a 5 year period: impact of the introduction of syndromic management.

Antimicrobial susceptibility testing was performed on isolates of Neisseria gonorrhoeae obtained from patients attending the City Health STD clinic in Durban, KwaZuluNatal, using the following drugs: penicillin, tetracycline, ciprofloxacin, ofloxacin, ceftriaxone, spectinomycin, erythromycin and azithromycin. These isolates were collected over a 6 year period from 1995 to 2000. Four hundred and fifteen strains were tested: 61 in 1995, 198 in 1997, 98 in 1998/99 and 58 in 1999/2000. A shift to the right is observed in the susceptibilities of N. gonorrhoeae to the currently recommended drugs in the syndromic management guidelines viz. penicillin, tetracycline, ceftriaxone, ciprofloxacin, spectinomycin and erythromycin. The prevalence of penicillinase-producing N. gonorrhoeae is currently c. 30%, whereas that of plasmid-mediated tetracycline-resistant N. gonorrhoeae is c. 50%. There is a definite association between the MICs of strains falling within the penicillin and tetracycline chromosomally resistant group, and strains exhibiting a decreased susceptibility to ciprofloxacin and ceftriaxone. The MICs of azithromycin showed a similar distribution when compared with erythromycin for 1999/2000 isolates. We postulate that the presence of efflux pumps might play a role in the increasing MICs that we observe among structurally unrelated groups of drugs. Furthermore, widespread use of these antimicrobials in the community may offer a selective advantage to the development of resistance. The implications of this are far reaching and the local susceptibility trends of N. gonorrhoeae need to be monitored constantly to direct therapy.

Effects of exogenous zinc supplementation on intestinal epithelial repair in vitro.

BACKGROUND: Substitution of zinc modulates antioxidant capabilities within the intestinal mucosa and improves intestinal wound healing in zinc-deficient patients with inflammatory bowel diseases. The aim of this study was to characterize the modulating effects of zinc on intestinal epithelial cell function in vitro. MATERIALS AND METHODS: The effects of zinc on intestinal epithelial cell morphology were assessed by phase contrast and transmission electron microscopy using the non-transformed small intestinal epithelial cell line IEC-6. Zinc-induced apoptosis was assessed by DNA fragmentation analysis, lactate dehydrogluase (LDH) release and flow cytometry with propidium iodine staining. Furthermore, the effects of zinc on IEC-6 cell proliferation were assessed using a colorimetric thiazolyl blue (MTT) assay and on IEC-6 cell restitution using an in vitro wounding model. RESULTS: Physiological concentrations of zinc (25 microM) did not significantly alter the morphological appearance of IEC-6 cells. However, a 10-fold higher dose of zinc (250 microM) induced epithelial cell rounding, loss of adherence and apoptotic characteristics. While physiological zinc concentrations (< 100 microM) did not induce apoptosis, supraphysiological zinc concentrations (> 100 microM) caused apoptosis. Physiological concentrations of zinc (6.25-50 microM) had no significant effect on intestinal epithelial cell proliferation. In contrast, physiological concentrations of zinc (12.5-50 microM) significantly enhanced epithelial cell restitution through a transforming growth factor-beta (TGFbeta)-independent mechanism. Simultaneous addition of TGFbeta and zinc resulted in an additive stimulation of IEC-6 cell restitution. CONCLUSION: Zinc may promote intestinal epithelial wound healing by enhancement of epithelial cell restitution, the initial step of epithelial wound healing. Zinc supplementation may improve epithelial repair; however, excessive amounts of zinc may cause tissue injury and impair epithelial wound healing.

Emergence of multidrug-resistant tuberculosis in a community-based directly observed treatment programme in rural South Africa.

OBJECTIVE: Although little studied in developing countries, multidrug-resistant tuberculosis (MDR-TB) is considered a major threat. We report the molecular epidemiology, clinical features and outcome of an emerging MDR-TB epidemic. METHODS: In 1996 all tuberculosis suspects in the rural Hlabisa district, South Africa, had sputum cultured, and drug susceptibility patterns of mycobacterial isolates were determined. Isolates with MDR-TB (resistant to both isoniazid and rifampicin) were DNA fingerprinted by restriction fragment length polymorphism (RFLP) using IS6110 and polymorphic guanine-cytosine-rich sequence-based (PGRS) probes. Patients with MDR-TB were traced to determine outcome. Data were compared with results from a survey of drug susceptibility done in 1994. RESULTS: The rate of MDR-TB among smear-positive patients increased six-fold from 0.36% (1/275) in 1994 to 2.3% (13/561) in 1996 (P = 0.04). A further eight smear-negative cases were identified in 1996 from culture, six of whom had not been diagnosed with tuberculosis. MDR disease was clinically suspected in only five of the 21 cases (24%). Prevalence of primary and acquired MDR-TB was 1.8% and 4.1%, respectively. Twelve MDR-TB cases (67%) were in five RFLP-defined clusters. Among 20 traced patients, 10 (50%) had died, five had active disease (25%) and five (25%) were apparently cured. CONCLUSIONS: The rate of MDR-TB has risen rapidly in Hlabisa, apparently due to both reactivation disease and recent transmission. Many patients were not diagnosed with tuberculosis and many were not suspected of drug-resistant disease, and outcome was poor.

The N-glycans of jack bean alpha-mannosidase. Structure, topology and function.

The acid hydrolase alpha-mannosidase, which accumulates in plant vacuoles and probably is involved in the catabolism and turnover of N-linked glycoproteins, is itself a glycoprotein with at least one high-mannose-type and one complex-type N-glycan. The puzzling finding that alpha-mannosidase stably carries its own substrate suggests that the N-glycans have unique topologies, and important functions in protein folding, oligomerization or enzyme activity. As a first step towards the elucidation of this enigma, we purified the N-glycans of jack bean alpha-mannosidase and determined their structures by sugar composition analysis, mass spectrometry and 1H-NMR. The structures of two N-glycans were identified in an approximate ratio of one-to-one: a glucose-containing high-mannose-type glycan (Glc1Man9GlcNAc2) and a small xylose- and fucose-containing complex-type glycan (Xyl1Man1Fuc1GlcNAc2). Isolation and sequencing of glycopeptides strongly suggests that one high-mannose-type and one complex-type glycan are linked to specific glycosylation sites of the large alpha-mannosidase subunit. The high-mannose-type glycan, which is a good substrate of the endoglycosidase (endo-H), can only be removed from the enzyme after denaturation and cleavage of disulfide bonds by a reducing agent, suggesting that this glycan is buried within the folded polypeptide and, thus, protected from its hydrolytic activity. Denaturation and reduction of the native enzyme led to a marked decrease in alpha-mannosidase activity. However, the activity could largely be recovered by renaturation in an appropriate renaturation buffer. In contrast, recovery of alpha-mannosidase activity failed when the high-mannose-type glycan was removed by endo-H prior to renaturation, indicating that this glycan appears to be important for enzyme activity.

Piperacillin/tazobactam in the treatment of Klebsiella pneumoniae infections in neonates.

Nosocomial Klebsiella pneumoniae infection is associated with a high mortality in neonates and antimicrobial therapy of these infections has been complicated by the emergence of multiresistant strains. These organisms remain susceptible to only a few antimicrobial agents, and some of these are not recommended for use in children. In this study the antimicrobial agents used in the treatment of 33 neonates with Klebsiella pneumoniae (K. pneumonia) infection in our tertiary neonatal unit, during an outbreak were: piperacillin/tazobactam (13), imipenem/cilastatin (17), cefotaxime (2), and ciprofloxacin (1). Extended-spectrum beta-lactamase production was detected in K. pneumoniae isolates from 18 of 33 (54.5%) neonates. All-cause mortality was 13 of 33 (39.4%) and there was no significant difference in mortality between neonates treated with imipenem/cilastatin (6 of 17 or 35.3%) and neonates treated with piperacillin/tazobactam (6 of 13 or 46.2%). The duration of antimicrobial therapy and total hospital stay was similar between neonates who received imipenem/cilastatin and those that received piperacillin/tazobactam. This report suggests that piperacillin/tazobactam may be a useful antimicrobial agent in neonatal infections caused by beta-lactamase-producing organisms.

Efficacy of twice weekly treatment for tuberculosis given under direct observation in Africa.

The efficacy of a 6 months course of twice weekly therapy with 4 drugs for tuberculosis, preceded by a 2-3 weeks intensive daily phase, is unknown. Implementation of this regime as community-based directly observed therapy in Africa is highly effective (85% completion rate); it is important to estimate the efficacy of the regime before advocating its widespread use and before conducting prospective trials. We retrospectively evaluated 109 consecutive adults with culture-positive pulmonary tuberculosis who had documented completion of treatment; 84 (77%) were traced and in 15 (14%) a history was obtained from a close relative; 10 (9%) had left the area. Nineteen patients were producing sputum and 4 of these were culture-positive for Mycobacterium tuberculosis, giving an estimated cure rate of 95% (95% confidence interval, 89-98%). Follow-up specimens revealed no acquired drug resistance and restriction fragment length polymorphism analysis of patient-paired specimens showed them to be nearly identical, indicating that treatment had failed or there had been early relapse. This preliminary study suggested that generally twice weekly 4-drug treatment for tuberculosis, given under direct observation, is curative in an acceptable proportion of patients. Prospective trials are indicated.

Eradication of a multiple drug resistant Salmonella paratyphi A causing meningitis with ciprofloxacin.

A previously healthy breast-fed baby was admitted at 10 days of age to a hospital in the north of Pakistan with diarrhoea and fever. He was treated for suspected sepsis with intravenous cefotaxime and tobramycin. Cultures of blood and faeces at that time proved negative. At 12 days of age, seizures began and examination of CSF revealed evidence of pyogenic meningitis but bacteria were neither seen microscopically nor isolated in culture. Ceftazidime was substituted for cefotaxime and carbenicillin was given also. Since the baby's condition continued to deteriorate with persistent fever, vomiting and recurrent seizures, he was transferred to the Aga Khan University Hospital, Karachi. Examination of CSF there confirmed the diagnosis of pyogenic meningitis and revealed Gram-negative bacteria. Cultures of CSF and faeces yielded Salmonella paratyphi A but the blood culture was negative. The isolate was found to be multiple antimicrobially resistant but sensitive to ciprofloxacin. Treatment with this drug was therefore started 3 days after the baby's admission to the Aga Khan Hospital. Within 36 h, improvement was observed. From then onwards, the baby made a progressive recovery and was healthy when seen at 7 months of age.

1H-NMR structural determination of the N-linked carbohydrate chains on glycopeptides obtained from the bean lectin phytohemagglutinin.

Phytohemagglutinin, the lectin of the common bean Phaseolus vulgaris, is a N-linked glycoprotein with one high-mannose-type and one xylose-containing oligosaccharide side chain per polypeptide. The high-mannose-type glycan is attached to Asn12 and the complex-type glycan to Asn60 [Sturm, A. & Chrispeels, M. J. (1986) Plant Physiol. 81, 320-322]. The structures of the oligosaccharides were elucidated from two glycopeptides obtained from the lectin by Pronase digestion, affinity chromatography on concanavalin-A--Sepharose and gel-filtration chromatography on a column of BioGel P-4. The N-linked glycan structures were investigated by 500-MHz 1H-NMR spectroscopy and were established to be: [formula; see text]

Purification and properties of arylmannosidases from mung bean seedlings and soybean cells.

Two arylmannosidases (signified as A and B) were purified to homogeneity from soluble and microsomal fractions of mung bean seedlings. Arylmannosidase A from the microsomes appeared the same on native gels and on SDS gels as soluble arylmannosidase A, the same was true for arylmannosidase B. Sedimentation velocity studies indicated that both enzymes were homogeneous, and that arylmannosidase A had a molecular mass of 237 kd while B had a molecular mass of 243 kd. Arylmannosidase A showed two major protein bands on SDS gels with molecular masses of 60 and 55 kd, and minor bands of 79, 39 and 35 kd. All of these bands were N-linked since they were susceptible to digestion by endoglucosaminidase H. In addition, at least the major bands could be detected by Western blots with antibody raised against the xylose moiety of N-linked plant oligosaccharides, and they could also be labeled in soybean suspension cells with [2-3H]mannose. Arylmannosidase B showed three major bands with molecular masses of 72, 55 and 45 kd, and minor bands of 42 and 39 kd. With the possible exception of the 45 and 42 kd bands, all of these bands are glycoproteins. Arylmannosidases A and B showed somewhat different kinetics in terms of mannose release from high-mannose oligosaccharides, but they were equally susceptible to inhibition by swainsonine and mannostatin A. Polyclonal antibody raised against the arylmannosidase B cross-reacted equally well with arylmannosidase A from mung bean seedlings and with arylmannosidase from soybean cells. However, monoclonal antibody against mung bean arylmannosidase A was much less effective against arylmannosidase B. Antibody was used to examine the biosynthesis and structure of the carbohydrate chains of arylmannosidase in soybean cells grown in [2-3H]mannose. Treatment of the purified enzyme with Endo H released approximately 50% of the radioactivity, and these labeled oligosaccharides were of the high-mannose type, i.e. mostly Man9GlcNAc. The precipitated protein isolated from the Endo H treatment still contained 50% of the radioactivity, and this was present in modified structures that probably contain xylose residues.

Structure, position, and biosynthesis of the high mannose and the complex oligosaccharide side chains of the bean storage protein phaseolin.

Phaseolin, the major storage protein of the common bean (Phaseolus vulgaris), is a glycoprotein which is synthesized during seed development and accumulates in protein storage vacuoles or protein bodies. The protein has three different N-linked oligosaccharide side chains: Man9(GlcNAc)2, Man7(GlcNAc)2, and Xyl-Man3(GlcNAc)2 (where Xyl represents xylose). The structures of these glycans were determined by 1H NMR spectroscopy. The Man9(GlcNAc)2 glycan has the typical structure found in plant and animal glycoproteins. The structures of the two other glycans are shown below. (Formula; see text) Phaseolin was separated by electrophoresis on denaturing gels into four size classes of polypeptides. The two abundant ones have two oligosaccharides each, whereas the less abundant ones have only one oligosaccharide each. Polypeptides with two glycans have Man7(GlcNAc)2 attached to Asn252 and Man9(GlcNAc)2 attached to Asn341. Polypeptides with only one glycan have Xyl-Man3(GlcNAc)2 attached to Asn252. Both these asparagine residues are in canonical glycosylation sites; the numbering starts with the N-terminal methionine of the signal peptide of phaseolin. The presence of the Man7(GlcNAc)2 and of Xyl-Man3(GlcNAc)2 at the same asparagine residue (position 252) of different polypeptides seems to be controlled by the glycosylation status of Asn341. When Asp341 is unoccupied, the glycan at Asn252 is complex. When Asn341 is occupied, the glycan at Asn252 is only modified to the extent that 2 mannosyl residues are removed. The processing of the glycans, after the removal of the glucose residues, involves enzymes in the Golgi apparatus as well as in the protein bodies. Formation of the Xyl-Man3(GlcNAc)2 glycan is a multistep process that involves the Golgi apparatus-mediated removal of 6 mannose residues and the addition of 2 N-acetylglucosamine residues and 1 xylose. The terminal N-acetylglucosamine residues are later removed in the protein bodies. The conversion of Man9(GlcNAc)2 to Man7(GlcNAc)2 is a late processing event which occurs in the protein bodies. Experiments in which [3H]glucosamine-labeled phaseolin obtained from the endoplasmic reticulum (i.e. precursor phaseolin) is incubated with jack bean alpha-mannosidase show that the high mannose glycan on Asn252, but not the one on Asn341, is susceptible to enzyme degradation. Incubation of [3H] glucosamine-labeled phaseolin obtained from the Golgi apparatus with jack bean beta-N-acetylglucosaminidase results in the removal of the terminal N-acetylglucosamine residues from the complex chain.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of the endoplasmic reticulum-associated precursor of concanavalin A. Partial amino acid sequence and lectin activity.

Concanavalin A (ConA), which is not a glycoprotein, is synthesized as a glycoprotein precursor (pro-ConA) which is post-translationally processed. This processing results in the loss of a small glycopeptide with a high mannose oligosaccharide. Carrington et al. (Carrington, D.M., Auffret, A., and Hanke, D.E. (1985) Nature 313, 64-66) determined the nucleotide sequence of a cDNA for pro-ConA, and in the derived amino acid sequence the only glycosylation site is in the middle of the molecule. Furthermore, the derived amino acid sequence of the putative precursor of ConA was found not to be colinear with that of ConA. Here we show that pro-ConA is located primarily in an endoplasmic reticulum-rich organelle fraction. Pro-ConA was purified from this fraction and subjected to amino acid sequencing. The first 12 amino acids at the N-terminal end of pro-ConA correspond to amino acids 119-130 of mature ConA, and to amino acids 30-41 of the putative pre-pro-ConA, the sequence of which was derived from the nucleotide sequence of a cDNA. Amino acid sequencing of a tryptic glycopeptide with the high mannose side chain showed that the first 17 amino acids of this peptide correspond to amino acids 154-170 of pre-pro-ConA. The last six amino acids in this series correspond to the first six amino acids of mature ConA. These data fully support the hypothesis of Carrington et al. that the biosynthesis of ConA involves a post-translational peptide cleavage, transposition, and ligation within the original polypeptide. Pro-ConA from the organelle fraction does not bind to Sephadex G-50, indicating that it has no lectin activity. The processing of pro-ConA apparently imparts biological activity to this lectin.

Antibiotic advice based on an intra-operative Gram-stain during cholecystectomy.

Intra-operative microscopy of the bile was performed during cholecystectomy in 335 patients. Based on the results, individual antibiotic advice was given. Bacteria were seen in the Gram-stained smear from 96 patients of whom 86 had a positive culture. In five patients a negative Gram-stain correlated with a positive culture (sensitivity 94.5%, specificity 95%, positive predictive value 89.5% and negative predictive value 97.5%). In only four patients (1.2%) did the antibiotic advice turn out to be wrong. Eight patients (2.4%) had signs of postoperative infection: one after wrong antibiotic advice, one who did not have prophylaxis because of false negative microscopy, four who did not have prophylaxis for clinical reasons but who had positive Gram-stains, and two despite apparently appropriate antimicrobial prophylaxis. An intra-operative Gram-stain as a guide to individual antibiotic advice given by a medical microbiologist during cholecystectomy is recommended.